TS Class 8

Telangana SCERT 8th Class English Guide Telangana State Unit 2A Oliver Asks for More Textbook Questions and Answers.

TS 8th Class English Guide Unit 2A Oliver Asks for More

PRE-READING (Motivotion/Picture Interaction):

Read the saying given below and answer the questions that follow.

Question 1.
What does the sentence mean ?
Answer:
This sentence means that there are many places in the world that can give happiness. Among all the places home is the best. Anyone can be happy at home.

Question 2.
Do you agree/disagree with the view expressed in the saying ? Why?
Answer:
Having a home and a family is a social status. Being in a family gives the feeling of living. Home is the safest and the happiest place in the world. One can feel secure and happy at home among one’s family. So I agree with the view expressed in the above statement.

Question 3.
Do you like your home ? Why ?
Answer:
Yes, I like my home because it is the happiest place for me. It is very pleasant and comfortable to live in. I get love and warmth of members of my family in my home. My parents care for me and do all they can do to make me happy. My mother keeps home always neat and clean. The surroundings of my home are also beautiful.

ORAL DISCOURSE:

Question.
Talk on – “The feelings of a homeless child.”
Answer:
Homeless children are the kids who are wandering on the streets. They are deprived children. They become homeless because of several reasons. Some of them leave homes to explore the world. Some others leave their homes in short temper. Some others are unlucky fellows. Having lost their parents they become homeless. Poverty is one of the main reasons.

A homeless child suffers from want of love and affection. They miss their near and dear. There is no one who takes care of them. Hence the homeless child strongly wants love and affection from others. The homeless children are left alone on the street. They Eire hungry, thirsty and frightened. They are surrounded by thousands of unknown people. They beg for money on the streets. They want to play like other children they want to go to school and study like other children and they want to grow up in the care of their parents like other children.

They curse themselves why all this has happened only to them. They want someone who can understand them well. They want the company of others. They don’t want sympathy from others but they want to be friends with others. They suffer from problems like anxiety and aggressiveness as they are affected by emotions and dejected from parental love. They suffer from loneliness. They lack smile and starve from hunger for weeks. They want a helping hand which can give them protection.

They aspire that one day they will have a home. They don’t want to be a homeless destitute wandering here and there.

Comprehension:

Answer the following questions.

Question 1.
How did Oliver feel when he was asked to appear before the live board?
Answer:
Oliver had no clear idea of a live board. He was rather astonished by the information. He was not quite certain whether he- ought to laugh or cry.

Question 2.
Why did Oliver tremble and cry in the white-washed room?
Answer:
In the white-washed room Oliver appeared before the members of the live board. He was frightened on seeing so many gentlemen in the room. The beadle gave Oliver a tap on his back with a cane. So he trembled and cried in the white-washed room.

Question 3.
“What is that, sir?” inquired poor Oliver. What does ‘that’ refer to?
Answer:
‘That’ refers to the word, ‘orphan’. What Oliver means is that he doesn’t know the meaning of the word orphan’.

Question 4.
What kind of people were the members of the board? Justify your opinion.
Answer:
The members of the board were merciless, selfish and cruel. They did not offer adequate food to the children in the workhouse. They used the children for picking oakum. When Oliver asked for more food, they ordered instant punishment. They pasted a notice on the outside of the gate of the workhouse, offering a reward of five pounds to anybody who would take Oliver Twist off the hands of the parish.

Question 5.
What main differences do you notice between the children and the master? (Observe the physical appearances, dress, behaviour, etc.) What can you infer from these differences?
Answer:
Children were weak and thin. They wore plain clothes. They were afraid of their master. They had a great respect for him. But the master was fat. He wore expensive clothes. He behaved mercilessly and cruelly.

Question 6.
How do you look at Oliver’s request, ‘Please, sir, I want some more!’? What compelled him to say this?
Answer:
He was forced to go and request for more food as he was desperate with hunger and reckless with misery. The situation forced him to go and request his master for more food. It shows the pitiable and helpless condition of the boy.

Question 7.
What happened to Oliver at the end of the story?
Answer:
At the end of the story he was given instant punishment. Next morning a bill was pasted on the outside of the gate, offering a reward of five pounds to anybody who would take Oliver Twist off the hands of the parish. In other words, five pounds and Oliver Twist were offered to any man or woman who wanted an apprentice to any trade, business, or calling.

Question 8.
Do you find children like Oliver around you? How would you help them to live better?
Answer:
Yes. I find a few children like Oliver in some places. I would help them by giving my used clothes. I request my parents to give them good food. I would admit them in a good orphanage for food and education with the help of my teachers and parents.

Vocabulary:

I. Look at the underlined part in the following sentence.
Answer:
“You have come here to be educated…”, said the red-faced gentleman.
The word ‘red-faced’ is called a Compound Adjective.
The phrase red-faced gentleman’ is a short form of ‘a gentleman with a red face’.

Exercise – 1:

Question 1.
Pick out the phrases with Compound Adjectives from the story or elsewhere and write how they can be rewritten to express the same meaning.
Answer:
Phrases with compound Adjectives and their rewritten form with the same meaning :
(a) white-washed room : a room with white wash
(b) well-educated man : a man with well education
(c) old-aged people : people in old age
(d) narrow-minded person : a person with narrow mind
(e) short-tempered teacher : a teacher with short temper
(f) well-behaved student : a student with well behaviour
(g) cold-hearted person : a person with a cold heart
(h) quick-drying glue : the glue that dries quickly
(j) high-priced car : car with high price
(j) man-made mistake : a mistake made by man

Exercise – 2:

Question 2.
Change the underlined parts in the following paragraph into Compound adjectives. Rewrite the paragraph in your, notebook.
Sachin Tendulkar is a cricketer who is famous all over the world. He is a batsman playing with right hand. He has many world records to his credit which are mind blowing. Besides all these, he is a person with a kind heart. He works with an NGO (Non-Governmental Organization) based in Mumbai to help more than 200 orphans every year.
Answer:
Sachin Tendulkar is a world-famous cricketer. He is a right-handed batsman. He has many mind-blowing world records to his credit. Besides all these, he is a kind-hearted person. He works with a Mumbai-based NGO (Non-Governmental Organization) to help more than 200 orphans every year.

Exercise – 3:

Question 3.
Fill in the blanks with appropriate compound adjectives from the box given below.

deep-rooted, old-fashioned, well-mannered, soft-spoken, brand-new

Latha is a ________ girl. She speaks kindly with her classmates. Look at her, she is wearing an ________ dress. She does not like to wear ________ dresses. Don’t you think Latha is a ________ girl?
Answer:
Latha is a soft-spoken girl. She speaks kindly with her classmates. Look at her, she is wearing an old-fashioned dress. She does not like to wear brand-new dresses. Don’t you think Latha is a well-mannered girl?

Grammar:

I. Look at the following sentence taken from the story.

‘The boy is a fool.’ said the gentleman in the white waistcoat.
As you know, the above underlined expression, can be changed into a question.
How do we change the above statement into a question? By putting the auxiliary verb before the subject ‘the boy’.

Look at some more sentences.

1. ‘I understand that he asked for more.’
‘Do I understand that he asked for more?’

2. ‘Oliver asks for more’
Does Oliver ask for more?

3. ‘The boys took their places.’
Did the boys take their places?

These sentences are changed into a question by placing ‘do/does/did at the beginning, such questions are called Yes / No questions.

Exercise:

Change the following statements into Yes/ No questions.

Question 1.
Oliver was frightened at the sight of so many gentlemen.
Answer:
Was Oliver frightened at the sight of so many gentlemen?

Question 2.
You are an orphan.
Answer:
Are you an orphan?

Question 3.
You say your prayers every night.
Answer:
Do you say your prayers every night?

Question 4.
You will pick oakum tomorrow morning.
Answer:
Will you pick oakum tomorrow morning?

Question 5.
Mr. Bumble rushed into the room.
Answer:
Did Mr. Bumble rush into the room?

Question 6.
They can devour the big bowl.
Answer:
Can they devour the big bowl?

Question 7.
Boys have generally excellent appetites.
Answer:
Have boys generally excellent appetite?

Detailed Rules for Framing Yes/No Questions:

1. If there is one verb in the statement and the verb is a helping verb, simply switch the positions of the subject and verb.
Statement – Question
Raju is a singer. – Is Raju a singer?
Children will come here. – Will children come here?

2. If there are two or more verbs, simply switch the positions of the subject and the first verb.
Statement-Question
Sindhu is eating biscuits. – Is Sindhu eating biscuits?
Aparna has bought a car. – Has Aparna bought a car?
Manju has been sleeping since 8 a.m. – Has Manju been sleeping since 8 a.m.?

3. If there is one verb, and the verb is not a helping verb, the process is more complex.

(a) Add ‘Do’ at the beginning of the sentence.
Statement – Question
They live in that house.-Do they live in that house?

(b) If the main verb carries a third person singular ‘s’, move that ‘s’ to Do, making it Does.
Statement – Question
Balaji drives a car. – Does Balaji drive a car?

(c) If the main verb carries past tense, move the past tense to Do, making it Did.
Statement – Question
Keerthana played tennis yesterday. – Did Keerthana play tennis yesterday?

4. In American English, the helping verb ‘have’ functions like a main verb in questions. This is not common in British English.
Statement – Question
You have a bad cold. – Do you have a bad cold? (American English) (or) Have you a bad cold? (British English)

II. Read the following sentence taken from the story.

“You were brought up by the parish, weren’t you?”
In this sentence ‘weren’t you?’ at the end is called a question tag. Question tags are used to get information or confirmation. The question tags are positive if the statements are negative. And if the statements are positive, question tags are negative. These tags are short / contracted form of questions. If the statement has an auxiliary, the tag begins with an auxiliary. In case it does not have an auxiliary, it will begin with do/does/did.

Read the following dialogue to understand the usage of question tags.
Ramu : The weather is good today, isn’t it?
Vijay : Indeed, Ramu.
Ramu : How about going out now? Hope you’ll join me, won’t you?
Vijay : I’ve got some important work now, I am afraid.

Exercise:

Read the following dialogue that took place at a party. Add suitable question tags to complete it.
Rohit : Hi, I’ve met you before, ________
Suma : No, I don’t think so.
Rohit : But your name is Vani, ________
Suma : No, it’s Suma! Anyway, glad to meet you.
Rohit : Me too. This is Rohit. The party seems to be really lively, ________
Suma : Yes, definitely. We enjoy ourselves a lot on such occasions, ________
Rohit : Yeah, we do.
Answer:
Rohit : Hi, I’ve met you before, haven’t I?
Suma : No, I don’t think so.
Rohit : But your name is Vani, isn’t it?
Suma : No, it’s Suma! Anyway, glad to meet you.
Rohit : Me too. This is Rohit. The party seems to be really lively doesn’t it?
Suma : Yes, definitely. We enjoy ourselves a lot on such occasions, don’t we?
Rohit : Yeah, we do.

Detailed information on Question Tags:

A tag question consists of two parts: a statement and a shortened yes/no question that refers to it and asks if the first statement is true. The two parts are separated by a comma.

• When the main sentence is positive, the tag is negative. When the main sentence is negative, the tag is positive.
• The noun in the first part becomes a pronoun in the tag.
• The second part (the tag) consists of a verb and pronoun only. A question tag repeats the helping verb of the main sentence.

Examples:

• You don’t like me, do you?
• You won’t tell him my secret, will you?
• He doesn’t speak German, does he?
• You’re coming to my party, aren’t you?
• She’s really good at chess, isn’t she?
• You haven’t done your homework, have you?

Note:
The tense of the tag is determined by the tense of the auxiliary/modal verb of the statement that precedes it. If the statement does not use an auxiliary/modal (i.e., it is in the present or past simple tense), then the auxiliary to do must be used.

• She comes from Korea, doesn’t she?
• You like heavy metal music, don’t you? –
• He got top grade in the maths test, didn’t he?
• I really messed up, didn’t I?

Note: If the subject + verb combination is ‘I am’ , the tag of that statement is aren’t I?
Example: I am a student, aren’t I?

Note: If the subject is ‘this /that’, it becomes it in question tag. If the subject is these / those, it becomes they in question tag.
Examples :
This is your dog, isn’t it?
That wasn’t your mom, was it?
These movies are wonderful, aren’t they?

III. Editing:

Read the following passage. Every numbered sentence has an error. Identify and edit it.
(1) When Rohit was nine, his family lived for a small town. (2) His father Rajarao were a clerk in Rao & Rao Company. (3) Janaki, Rohit’s mother, was an housewife. She used to be alone in the daytime when Rohit was at school, and Rajarao, in his office. (4) She wanted to has a pet. (5) She asked Rohit’s father several time for a pet.
Answer:
(1) When Rohit was nine, his family lived in a small town. (2) His father Rajarao was a clerk in Rao & Rao Company. (3) Janaki, Rohit’s mother, was a housewife. She used to he alone in the daytime when Rohit was at school, and Rajarao, in his office. (4) She wanted to have a pet. (5) She asked Rohit’s father several times for a pet.

Writing:

I. Anne Frank was a little girl of thirteen. She was as lonely as Oliver Twist. When the German army invaded her country, she had to hide in a smart building with her family. She suffered a lot. She recorded her feelings and thoughts in her diary.

Friday, 1st October, 1942.
Just for fun, I am going to tell you each person’s first wish, when we are allowed to go out again. Mrs. Van says, ‘If I go out, I’ll eat cream cakes.’ Dussel says, ‘If I am let free, I’ll run to see my wife Lotje.” Mummy says, ‘I will have a cup of coffee.’ Peter says, ‘I will go to the cinema.’ I long for so many things. But Hong for a home of our own.

1. What did Anne write in her diary?
personal feelings/thoughts/reflections
events other than routine
future plans

2. Did you notice any variety in the sentences?
3. Are all the sentences connected with each other properly?

After facing the live board, Oliver returned to his bed crying. He sat up to write his diary. Now, imagine you are Oliver Twist. Attempt a diary entry with the above features in mind.
Answer:

Diary Entry

27 August.

O! God, I am afraid of the live board. They seem to be very cruel. I know they don’t show mercy on children like me. I wish I had my mother and father. I don’t know-what happened to my parents. I feel like going out of this workhouse. But I know there is no way to escape from this place. They asked me to pick oakum from tomorrow. If my parents were alive, they wouldn’t send me for picking oakum. May God give the members of the board good and kind heart!

Oliver Asks for More Summary in English

(This is an extract from the novel ‘Oliver Twist’ written,by a British novelist, Charles Dickens (1812-70). It is the story of an orphan boy named Oliver, who is brought to a children’s home.)

In the workhouse of an unidentified place, on an unspecified date, a child is bom. As the infant struggles for survival, the pretty young mother’s life is ebbing. An old pauper, Mrs. Thingummy, who has assisted the attending surgeon, explains to the doctor that the young woman was unknown and had been brought in the night before, after being found lying in the street.

At the sound of her child’s voice, the mother murmurs faintly, “Let me see the child and die.” Both wishes are granted. After giving him one kiss, she dies. The new born child is Oliver Twist.

Young Oliver is kept in the workhouse for eight or ten months, but the accommodations there not being suited to the care of infants, he is transferred to a private asylum. This haven for juveniles is run by Mrs. Mann, an entrepreneur who earns money by starving the children and pocketing most of the allowance dispensed for their sustenance. The youngsters perish with regularity, but investigation always sustains the report that death was due to natural causes or “accident.”

Under this gentle system of charity, Oliver Twist spends his first nine years. His birthday is celebrated with a beating and confinement in the coal cellar with two other malefactors for “atrociously presuming to be hungry.”

While Oliver is thus disposed of, Mr. Bumble, a minor church official, suddenly appears at the garden gate. Mrs. Mann keeps him waiting until the prisoners are released. After Bumble is admitted, he demonstrates his sense of importance by rebuking Mrs. Mann before they then join in a demonstration of mutual hypocrisy as he partakes of her gin.

The self-important Bumble has come on business. His efforts to discover the identity of Oliver’s father or the origin of his mother have failed. The authorities have ruled that the orphan is to be returned to his birthplace — the workhouse. In the meantime, Oliver has been removed from the coal bin and has been made presentable. He is now brought forth and delivered to Mr. Bumble, who escorts him to his new home.

That very evening, the board in control of workhouse affairs is meeting, and Oliver is s promptly summoned to face that august body. After being admonished to persevere in gratitude for the blessings given him so far, the boy is told that he is to be further favoured by being taught a trade – picking oakum, (a tar-soaked fibre used as a caulking in ships) starting the next morning.

Following this scene the author discloses that the authorities have just devised a new food menu for the workhouse. The paupers are restricted to a pitifully small portion of food, and other callous measures are put into practice. The policy succeeds in reducing the workhouse population, although many depart for the graveyard.

After several months of the most meagre meals, the boys are desperate with hunger. One night at dinner, one child tells the others that if he does not have another bowl of gruel he might eat one among them who sleeps next to him in the workhouse. Terrified, the workhouse boys hold a council meeting to select one among them as the member to go and request the authorities for more to eat. The children at the workhouse cast lots (a game of choice by chance), determining that whoever loses shall be required to ask for more food for the boy.

Oliver loses, and after dinner, the other children insist that Oliver should ask for more food at supper. That evening after the skimpy ration of thin gruel has been consumed; Oliver approaches the fat workhouse master and asks for more. The master is overwhelmed with astonishment. In a state of agitation, Bumble rushes to inform the board, which is in session. The members are horrified; a gentleman in a white waistcoat is satisfied beyond all doubt that the culprit will end up on the gallows.

Oliver is instantly ordered to confinement. The next morning, a notice is posted on the gate offering five pounds to anyone who will accept Oliver Twist as an apprentice to any trade or – business.

About the Author:

Charles Dickens (1812-1870) is a well known English novelist. Due to his father’s imprisonment Charles left school and worked in a shoe factory. While he was working as an office boy he launched his writing career. His novels Oliver Twist, Great Expectations, Pickwick Papers, Bleak House, A Tale of two Cities and David Copperfield brought him name all over the world. He went on lecture tours to America and got literary reputation. He focussed on social issues and human ailments in his works.

Glossary:

extract (n) : passage that has been taken
orphan (n) : a child whose parents are dead
strides (n) : long steps
grasping (v) : taking a firm hold
trotted (v) : ran and walked fast taking short quick steps
board (n) : a group of people who have power to make decisions and control an organisation
appear (v) : to be seen
forthwith (adv) : immediately/at once
defined notion : clear idea
live board : board with life
astonished (adj) : very surprised
bow (v) : move one’s head or the top half of one’s body forwards and downwards as a sign of respect
brushed away : dropped
lingering (v) : exist somewhere
frightened (adj) : afraid/feeling fear
tremble (v) shake in a way you cannot control because you are very nervous
beadle (n) : a minor church official
tap (n) : hit somebody quickly and lightly
parish (n) : a church committee
gruff (adj) : unfriendly ; deep and rough
stammered (v) : spoke with difficulty, repeating sounds or words often stopping
oakum (n) : loose fibre obtained by untwisting and picking apart old ropes
surly (adj) : serious or angry
gruel (n) : a thin liquid food of oats, rice, etc.
devoured (v) : ate hungrily or quickly
stray (adj) : separated

splashes (n) : small amounts of liquid that falls onto
appetite (n) : the desire to eat; hunger
voracious (adj) : wanting great quantities of food
lots (n) : using a method of choosing somebody to do something
cast (v) : through something
ranged (v) : moved around
desperate (adj) : worried/distressed
nudged (v) : pushed
advancing (v) : moving/walking forward
stupefied (adj) : shocked
paralyzed (v) : became motionless
ladle (n) : a long handled spoon used to serve liquids
countenance (n) : a person’s face or facial expression
confinement (n) : putting in a prison or a closed room
apprentice (n) : one who works under a skilled person
calling (n) : a profession or career

Telangana SCERT TS 8th Class Physics Study Material Pdf 9th Lesson Electrical Conductivity of Liquids Textbook Questions and Answers.

TS 8th Class Physics 9th Lesson Questions and Answers – Electrical Conductivity of Liquids

Reflections on concepts

Question 1.
Give examples for good solid conductors and liquid conductors.
Answer:
Examples for good conductors in solids: Metals like copper, aluminium, gold, silver, iron etc.
Examples for good conductors in liquids: Lemon juice, vinegar, dilute sulphuric acid etc.

Question 2.
Give examples for poor solid conductors and liquid conductors.
Answer:
Examples for poor conductors solid: Rubber, plastic, glass, dry wood etc.
Examples for poor conductors liquid: Distilled water, coconut oil, vegetable oil, sugar solution etc.

Question 3.
Give two examples for electrolytes.
Answer:
Electrolyte: Any substance that dissociates into ions when dissolved in a suitable medium or melted and thus forms a conductor of electricity.
Eg:

1. CuSO₄ (Copper Sulphate)
2. AuCl₂ (Auric Chloride)
3. AgNO₃ (Silver Nitrate)

Question 4.
Draw the diagram of Electrolytic cell and explain.
Answer:

Apparatus: Battery, Key, Rheostat, Voltameter, Electrolyte, Cathode and Anode Explanation:

1. Connections are made as per the circuit.
2. An electrolyte (CuSO4) is taken in voltameter.
3. Two metals electrodes are immersed in the electrolyte.
4. The electrode connected to negative of the Battery is known as cathode and the electron connected to positive of the battery in known as anode.
5. By pressing the plug key the circuit is closed and current flows in the circuit.
6. By adjusting the Rheostat we can increase or decrease the current in the circuit.
7. When current flows in electrolyte it dissolve into Cu⁺ and SO\(\overline{4}\).
8. The copper ions are deposited on cathode.

Application of concepts

Question 1.
Which energy is cause for glowing of bulb in electrolytic cell?
Answer:
The chemical energy is converted into electrical energy by electrolysis method. This causes the glowing of bulb.

Question 2.
What do you add to distilled water for making it to conduct electricity?
Answer:
By dissolving materials like acids, bases, salts such as common salt, lemon juice, hydrochloric acid, sulphuric acid, vinegar, caustic soda etc, to distilled water for making it to conduct electricity.

Question 3.
Kavya observed that a discharged dry cell which kept in sunlight by her father for few hours got ability to glow LED. She got many doubts and questions to raise. Can you guess those questions or doubts?
Answer:

1. How the discharged dry cell, being charged by sunlight?
2. Can we use these dry cells to some more electrical appliances?
3. How sunlight is helpful in recharging the dry cell?
4. Is it possible to recharge the dry cell in another ways?
5. Which material get charged in dry cell, when kept in sunlight?
6. What is the mechanism during this process?

Question 4.
Make a battery from four lemons and test It with a LED In the circuit.
Answer:
To make a battery from four lemons.
Required materials: 4 juicy lemons, 4 copper plates, 4 paper clips, 5 alligator clips, 1 red LED, conducting wires.

Procedure: Take 4 lemons and connect each lemon with lemon by clipping one end of an alligator dip to a copper and the other to a paper clip as shown in the circuit Then include one LED into the circuit. Leave the inserted for 20 to 30 minutes. Observation: The LED glows.

Question 5.
Collect the Information and make list of good conductors and bad conductors. How do you use this information in your daily life works?
Answer:

Good conductors	Bad conductors
1. Copper	1. Plastic
2. iron	2. Glass
3. Aluminium	3. Wood
4. Silver	4. Rubber
5. Gold	5. Paper

Conductors are used in wires to allow electricity to flow. So it can power our appliance insulators like plastic coverings around the wires would stop electricity and prevents electric shock.

Higher Order Thinking Questions

Question 1.
If the key is to be coated with aluminium instead of copper, what changes do we need to make in the experiment of coating on iron key with copper?
Answer:

1. Coating on iron key with copper the copper sulphate electrolyte is taken in voltameter.
2. When the circuit in closed current flows.
3. Here the iron key is taken as cathode.
4. Due to the flow of current CuSO₄ dissociates into Cu⁺ and SO^–₄ ions.
5. All the Cu ions goes to the cathode.
6. Since we have taken the key as cathode copper gets deposited on the key.
7. If the current is passed through few minutes the iron key is changed as copper key.
8. It is taken out and dried.

Question 2.
Is plastic coated by the process of electroplating? Why?
(Or)
Is coating on plastics possible like that of metal objects.
Answer:
No. It is not possible.
The plastic is electrically non-conductive and cannot be immersed in a plating solution and coated in the way that metal objects can.
Some method was therefore needed whereby a conductive film could be deposited onto the surface of the plastics to provide the basis for subsequent electrode position.

Multiple Choice Questions

Question 1.
Which of the following is also used in ornamentation and decoration [ ]
a) Electro typing
b) Electroplating
c) Electro printing
d) Galvanizing
Answer:
b) Electroplating

Question 2.
Pure water is [ ]
a) Electric conductor
b) Semiconductor
c) Insulator
d) Resistor
Answer:
c) Insulator

Question 3.
The material which do not allow electric current to pass through it is known as [ ]
a) Electric conductor
b) Insulator
c) Electric resistance
d) semiconductor
Answer:
b) Insulator

Question 4.
Electroplating is possible through [ ]
a) Electrolysis
b) Chemical process
c) Dissolving
d) Filtration
Answer:
a) Electrolysis

Question 5.
One of the following is not an electrolyte [ ]
a) Sulphuric acid
b) Lemon juice
c) Tamarind juice
d) Detergent solution
Answer:
c) Tamarind juice

Suggested Experiments

Question 1.
Conduct an experiment for coating on iron key with copper by electroplating method and prepare a report.
Answer:
Aim: Coating copper on iron key by the process of electroplating.
Required materials: Copperplate (2cm X 5 cm), a key made of iron, glass beaker,
battery cell, connecting wires, water, copper sulphate crystals, and sulphuric acid.

Procedure:

1. Prepare a concentrated solution of copper sulphate by dissolving copper sulphate crystals in pure water.
2. Pour the solution in a beaker and add a few drops of dilute sulphuric acid to increase the conductivity.
3. Tie one end of the connecting copper wire to the iron key to be coated with copper. Connect its other end to the negative terminal of a battery and suspend it into the copper sulphate solution.
4. Suspend the copper plate into copper sulphate solution from the positive end of the battery through a switch.
5. Put the switch on for about 10 minutes, then switch off the circuit and take the iron key out.

Observations: Iron key get coated with copper.
Result: Iron key get coated with copper by the process of electroplating.

Question 2.
Conduct an experiment for testing the electric conductivity of liquids.
Answer:

1. Take a LED, dry cell, metal pins, rubber cap of injection bottle and wires for making connections. Set up an electric circuit as shown in the figure
2. See that two metal pins, pass through the cap and should have a very small Rubber
   gap between them. So that the pins are fairly’ closer but not touching each other.
3. The LED does not glow when pins are separated by the small distance.
4. Now join the force ends of the pins together by pressing them for a moment and make sure that LED glows. If we release the pins they get separated and LED should not glow. This becomes our tester.
5. Now fill the rubber cap with different liquids one after another and in each case check whether the LED glows or not. Note your observations in table.

Table (Text. P. No. 122)

Liquid	LED glows Yes/No	Good conductors/ poor or bad conductors
1. Distilled water	No	had conductor
2. Drinking water	Yes	good conductor
4. Coconut oil	No	bad conductor
5. Lemon juice	Yes	good conductor
6. Vinegar	Yes	good conductor
7. Kerosene	No	bad conductor
8. Vegetable oil	No	bad conductor
9. Sugar solution	No	bad conductor
10. Milk	No	bad conductor
11. Honey	No	bad conductor

vi. From the above activity we conclude that some liquids are conductors (LED glows) and some liquids are had conductors (LED does not glow)
(a) Why doesn’t the lED glow in all the cases? Or why doesn’t the LED remain off
in all the cases for different liquids?
Answer:
Some liquids such as lemon juice and vinegar are good conductors of electricity. When these liquids are placed between the two pins of the tester allow electric current to pass through. the circuit is closed and the LED glows. Some liquids such as distilled water, coconut oil are had conductors of electricity. When these liquids are placed between the two pins of the tester do not allow electric current to pass through, the circuit is opened and the LED does not glow.

b. List out the good conductors from table.
Answer:
Good conductors:
1. Lemon Juice
2. Vinegar
3. Drinking water.

Question 3.
Conduct an experiment for testing the electric conductivity of electrolytes.
Answer:
Aim: Testing of electric conductivity of electrolyte.
Apparatus: Battery, Tap key, Rheostat, Voltameter, Electrolytes, Electrodes, Electric Bulb.
Circuit:

Procedure:

1. Connections are made as per the circuit diagram.
2. An electric lamp is connected in series in the circuit.
3. When the Tap key is pressed current flows in the circuit.
4. The copper sulphate solution dissociates.
5. As and when plug is closed the bulb glows.
6. It indicates that the electric conductivity is taking place in electrolyte.
7. This experiment can be done with different electrolytes.
8. If electrolyte is charged the brightness in the bulb also changes.
9. Hence with this experiment, we can say electric conductivity takes places in electrolytes.

Suggested Projects

Question 1.
Collect the information from various sources on the applications of electroplating in daily life and prepare a report on that.
Answer:
Applications of Electroplating:

1. Electroplating is widely used in industry for coating metal objects with thin layer of different metals.
2. In electroplating, an inferior metals which are effected by the atmospheric humidity, are coated with superior metal.
3. Electroplating is done with view of repairing worn-out parts of machinery.
4. Electroplating is also used in ornamentation and decoration.
5. Processed food items are preserved in tin-coated iron cans. Tin is less reactive
   to the food than iron. So the cans are made by electroplating tin on iron.
6. Iron is coated with zinc metal, iron becomes more resistant to corrosion and formation rust. So zinc-coated iron is used for bridges and in automobiles.

Question 2.
In many of the activities in this chapter, we have used a tester made up of LED. Can we avoid LED and use something else as a tester? Collect the information and make a model.
Answer:
When current flows in a wire, a compass needle kept nearby gets deflected. Even the current is small, the deflection of the magnetic needle can be seen. To make a tester of magnetic compass needle, take a cardboard tray from inside of a discarded matchbox.

Wrap an electric wire a few times around the cardboard tray. Place a small compass needle inside it. Now connect one free end of the wire to a terminal of a two cell battery. From the other terminal of the battery connect another wire. Now the tester with two free ends of wire is ready.

TS 8th Class Physics 9th Lesson Electrical Conductivity of Liquids Intext Questions

Think and Discuss

Question 1.
Why some material allows electric current to pass through them and why some do not? (Text. P. No. 121) (Conceptual understanding)
Answer:
In some materials Like metals, they are good conductors of electricity because the electrons are free to move in a network of metal atom. But in materials such as plastic there will be no free electrons occur. Hence they do not conduct electricity.

Question 2.
If a battery is packed in a box and if only two wires from two terminals are given out, how can we decide the positive and negative terminal of the battery? (Text. P. No. 125) (Information Skills & Projects)
Answer:
Connect a voltmeter probes to the battery terminals, if the voltage is shown as a negative, then switch the voltmeters probes around at the battery end so it shows the voltage as a positive reading in the voltmeter. From this activity, we can decide the positive and negative terminals of the battery.

Question 3.
What is electrolysis? (Conceptual understanding)
Answer:
Electrolysis: The process of decomposition of a chemical compound in a solution, when an electric current passes through it is called electrolysis.
Examples: CuSO₄ → Cu⁺²+SO^–₄

Question 4.
Discuss with your teacher or collect the information about electrolysis method from your school library books.
Answer:
Student’s Activity

TS 8th Class Physics 9th Lesson Electrical Conductivity of Liquids Activities

Activity – 1: Testing the material to know which allows electric current to pass through it: (Text. P. No. 120)

Question 1.
Conduct an activity to know which materials allow electric current through them and define conductors and bad conductors of electricity.
Answer:

• Take a torch bulb or LED (Light Emitting Diode), a dry cell, a wooden sheet, two drawing pins, a key (safety pin) and pieces of connecting wires.
•  Set up the electric circuit as shown in the figure.

• Place the key in ON position. You may see that the bulb begins to glow.
• Now replace the key by a nail. Observe whether the bulb glows or not.
• Repeat the activity using different types of materials instead of the nail, say a strip of paper, a piece of chalk, a drinking straw, a piece of plastic, a paper clip, a rubber eraser, etc.

Noting in each case whether the bulb glows or not (observations) in a table.
Table (Information Skills & Projects)

vi. From the above activity we conclude that some materials allow electric current to pass through them. We call them as good conductors of electricity.
vii. Some materials do not allow current to pass’. through them. They are called bad or poor conductors of electricity.

Activity- 2 :
Testing the electric conductivity of liquids (Text. P. No. 122)

Question 2.
Do the liquids allow electric current to pass through them? Test the electric conductivity of liquids through an activity.
Answer:

• Take a LED, dry cell, metal pins, rubber cap of injection bottle and wires for making connections. Set up an electric circuit as shown in the figure
• See that two metal pins, pass through the cap and should have a very small gap between them. So that the pins are fairly closer hut not touching each other.
• The LED does not glow when pins are separated by the small distance.

• Now join the force ends of the pins together by pressing them for a moment and make sure that LED glows. If we release the pins they get separated and LED should not glow. This becomes our tester.
• Now fill the rubber cap with different liquids one after another and in each case check whether the LED glows or not. Note your observations in table.

Table (Text. P. No. 122)

Liquid	LED glows Yes/No	Good conductors/ poor or bad conductors
1. Distilled water	No	bad conductor
2. Drinking water	Yes	good conductor
4. Coconut oil	No	bad conductor
5. Lemon juice	Yes	good conductor
6. Vinegar	Yes	good conductor
7. Kerosene	No	bad conductor
8. Vegetable oil	No	bad conductor
9. Sugar solution	No	bad conductor
10. Milk	No	bad conductor
11. Honey	No	bad conductor

vi. From the above activity  we conclude that some liquids are conductors (LED glows) and some liquids are had conductors (LED does not glow)

(a) Why doesn’t the LED glow in all the cases? Or why doesn’t the LED remain off
in all the cases for different liquids? (Conceptual understanding)
Answer:
Some liquids such as lemon juice and vinegar are good conductors of electricity. When these liquids are placed between the two pins of the tester allow electric current to pass through. the circuit is closed and the LED glows.

Sonic liquids such as distilled water, coconut oil are bad conductors of electricity. When these liquids are placed between the two pins of the tester do not allow electric current to pass through, the circuit is opened and the LED does not glow.

b. List out the good conductors from table.
Answer:
Good conductors:

1. Lemon juice
2. Vinegar
3. Drinking water.

Activity – 3:
Transforming a poor electric conductor into a Lood conductor.’ (Text. P. No. 124)

Question 3.
How do you convert a poor electric conductor into a good conductor?
(or)
Can we make poor conductors like distilled water to conduct electricity? Explain with an activity.
Answer:

• Take same amount of distilled water in three different containers.
• Dissolve small quantity of common salt in the water of first container.
• Dissolve the Copper Sulphate (Mylatuttam), lemon juice in 2nd and 3rd containers respectively.
• Take LED, dry cell, metal pins, rubber cap of injection bottle and wires for making connections. Set up an electric circuit as shown in figure.

• See that two metal pins, pass through the cap and should have a very small gap between them. So that the pins are fairly closer but not touching each other.
• Now fill the rubber cap with distilled water and the solutions of above three containers one after another and check whether the LED glows are not.
• Note your observations in table.

Table

Material	Does the LED glow? Yes/No	Good conductor/bad or poor conductor
1. Distilled water	No	Bad conductor
2. Dist. water + salt	Yes	Good  conductor
3. Dist. water + CuSO4	Yes	Good conductor
4. Dist. water + lemon juice	Yes	Good conductor

• From the above table we conclude that pure distilled water is a bad conductor of electricity, but water with salt is a good conductor of electricity.
• In this way distilled water is converted into conductor by adding salts.

(a) Why you are advised not to touch electric appliances with wet hands? (Applications to daily lift’)
Answer:
Water with salts is a good conductor of electricity and the current flowing through household electric appliances is vers’ high. Therefore, we should never touch the electrical appliances with wet hands.

Activity -4:
Testing the effect of electric current on potato : (Text. P. No. 125)

Question 4.
How do you test the effect of electric current on potato? (If solutions of different salts and acids conduct electricity, what do vegetables and fruits do? Let us try to find that out.) (Experimentation & F.I.)
Answer:

• Take a potato. Cut in into two halves and take LED one hail of it.
• Construct tester with LED bulb.
• Insert two copper wires of the tester into the potato leaving some distance (around 1 cm) between them.
• LED would glow. Leave the inserted wires for 20 – 30 minutes.
• A greenish-blue spot is seen on the potato around the wire connected to the positive terminal of the hatter’ But no such spot is seen around the other wire connected to the negative terminal.
• This greenish-blue spot on the potato around the wire connected to the positive terminal of the battery is due to chemical change in the potato.
• From this we conclude that there is chemical change in some fruits and vegetables due to the passage of current through them.

Questions based on the above Activity – 4

a. Does the LED glow?
Answer:
Yes, LED would glow.

b. What do you observe the surface of the potato after leaving the inserted wires for 20-30 minutes?
Answer:
A greenish-blue spot is seen on the potato around the wire connected to the positive
terminal of the battery. But no such spot is seen around the other wire connected to the negative terminal.

c. What could be the cause behind this change?
Answer:
This greenish-blue Spot on the potato around the wire connected to the positive terminal of the batter’ is due to a chemical change in the potato.

d. Will other vegetables also show electric conductivity?
Answer:
Yes, vegetables like tomatoes, onions also conduct electricity, since they have the highest acidity level, citrus fruits like apples, grapes, oranges, lemons are also excellent conductors due, to the high acidity level.

Activity -5 :
Make your own cell: (Text. R No. 127)

Question 5.
How do you make your own cell?
Answer:
Collect two injection bottles. Cut two 5 cm-long hits of thick copper wire. Use sandpaper to scrape about 1 cm of the coating off both ends of the wires. Break open a exhausted dry cell and remove its outer metal covering (made of zinc). Cut two 2 mm wide and 5 cm long strips from this zinc plate. Insert the copper wires and zinc strips into the rubber caps of the injection bottles as shown in figure. Ensure that the copper wire and zinc strips do not touch each other.

Now take a wire and connect the copper wire of one bottle with the zinc plate of the other bottle. Fill both bottles with dilute sulphuric acid. Carefully close the bottles with the caps in which the copper wires and zinc strips are inserted.

Your cell is ready. Take a LED. Attach two wires to its two terminals. Touch the wire from one terminal to the zinc plate and the wire from the other terminal to the copper wire. Did the LED light up? If not, change the connections vice-versa.

Questions based on the have Activity-5;

a. What other liquids can be used to make the cell? (info a lion Skills & Projects)
Answer:
Lemon juice, tamarind juice, tomato juice, and vinegar-like solutions which are acidic in nature can be used to make the cell.

b. Will the detergent solution be useful? Find it out for yourself.
Answer:
Detergents contain caustic soda which is a strong base. So detergent solution be useful.

c. How does the above cell function?
Answer:
The cell works on the process of electrolysis. Here the chemical energy is converted into electrical energy.

d. Can you compare sulphuric acid cell with dry cell? Which is good one? Why? (Conceptual understanding)
Answer:
Sulphuric acid cell contains liquid electrolyte dilute sulphuric acid and voltage of the cell is low. But dry cell contains solid electrolyte and voltage is comparatively high.

Lab Activity

Question 1.
How do you coat an iron key with copper by electroplating method. (Text. P. No. 128)
Answer:
Aim: Coating an iron key with copper by electroplating method.
Required material: Copperplate of size 2 cm x 5 cm, crystals of copper sulphate (blue vitriol), a key made by iron, glass beaker, water, sulphuric acid, battery and some connecting copper wires.

Procedure:

• Dissolve crystals of copper sulphate in pure water to prepare concentrated solution (deep blue in colour).
• Pour the solution in a beaker and add a few drops of dilute sulphuric acid to it.
• Tie one end of a connecting copper wire to the iron object (key) to be coated with copper.
• Connect its other end to the negative terminal of a battery.
• Suspend the tied iron object into the copper sulphate solution.
• Suspend the copper plate into copper sulphate from positive end of the battery through a switch as shown.
• Plate and key do not touch each other and are a little away from one another. Put the switch on for about lO minutes.
• When electric current is passed through the copper sulphate solution, the copper sulphate dissociates into copper and sulphate ions.

• Gets drawn to electrode connected to the negative terminal of the battery key and gets deposited on it.
• Thus one metal is coated with another material. This process is known electroplating.
• In this way we coat a iron key with copper by electroplating method.

Questions based on the above Lab Activity (Tert. P. No. 128)

a. Does the iron key get coated with a shiny, brown colour?
Answer:
Yes, the iron key get coated with a shiny, brown colour of copper metal. In this process of electrolysis cu₂’ ions are liberated from CuSO₄ (electrolyte) and deposited as copper metal iron key (cathode)

b. What is the colour due to?
Answer:
The shiny brown colour is due to the deposition of copper metal on iron key by the process of electroplating.

c. What will happen if you interchange the battery terminals?
Answer:
If we interchange the battery terminals electrolysis does not take place. This is because of the external battery supplies the electrons. They enter through cathode and come out through anode.

d. Why does copper get deposited on the iron key?
Answer:
When electric current is passed through the copper sulphate solution, the copper sulphate dissociate into copper and sulphate ions. The free copper gets drawn to
the electrode connected to the negative terminal of the battery arid gets deposited
on it.

Telangana SCERT 8th Class English Guide Telangana State Unit 1C A Letter to a Friend Textbook Questions and Answers.

TS 8th Class English Guide Unit 1C A Letter to a Friend

Questions and Answers:

Answer the following questions.

Question 1.
How did Suresh and Ramesh spend their childhood ?
Answer:
Suresh and Ramesh spent their childhood together happily. They played gilli-danda, hide and seek and kabaddi. They went for swimming in their local tank every Sunday.

Question 2.
Why did Ramesh’s family move to the city?
Answer:
Ramesh was educated. He went to the city in search of a job. So Ramesh’s family moved to the city.

Question 3.
What change did you observe in Ramesh?
Answer:
Ramesh used to live with his family in his childhood. He enjoyed peaceful life with his friends and family. His world had many people like father, mother, grandparents, cousins, uncles, friends etc. He was brought up with love and affection. But now he is leading a busy life. Now there is none except his wife and daughter in his life. He missed everybody. His daughter was brought up in a child care centre. He realised he missed the joy of his family and their company. He missed the fairy tales of his grandfather. He missed his real life.

Question 4.
Do you think Ramesh is happy in the city? Why?
Answer:
No. I don’t think Ramesh is happy in the city because he is leading a very busy life there. He has no time to bring up his child. He missed his real and enjoyable life that he enjoyed in his village with his parents and grandparents.

Question 5.
What made Ramesh write to Suresh?
Answer:
Ramesh lived in Hyderabad. He could not meet his friend Suresh when he visited Hyderabad. He felt very sorry for his busy life that did not allow him to meet his childhood friend. He wanted to apologise his friend for this and to remind him of his childhood days spent with him. He wanted to share his feelings with his friend as he could not meet him personally through a letter. This made him write to Suresh.

Project Work:

Observe any five families in your neighbourhood and draw your conclusions, advantages and disadvantages of living in a joint/nuclear family.

Advantages and Disadvantages of a Nuclear Family

A nuclear family is a family group consisting of father and mother and their children, who share living quarters. This can be contrasted with an extended family.

Nuclear family grows out of joint/extended family when there is migration from village to city for employment or other reasons where joint family is not possible due to paucity of needed larger residential accommodation, different occupation etc. That is why it is mainly seen in urban areas, cities and metropolis.

Nuclear families may also exist in rural areas because the joint family cannot go on indefinitely owing to physical and social limitations. There is a limit to the number of people a house can accommodate and thus, there is bound to be fission into smaller nuclear families in the family cycle of development.

Merits of a Nuclear Family:

Unlike the joint family, there is greater degree of freedom for spouses in the nuclear family. The status of the woman is higher and she often takes up employment outside the home. The material well-being of children, such as healthcare and education, is higher because of more resources available. Nuclear families are adaptable to social change.

Drawbacks:

The nuclear family misses all the advantages of joint living. It is too isolated and uncon¬nected to elicit support or assistance during need or crisis. Its limited size poses practical prob¬lems for child rearing and care, more so when the mother works outside.

Children are deprived of a wider social world, emotional bonding, love and affection that a joint family provides. The old parents are left in the village or at old age homes without personal care.

Advantages and Disadvantages of a Joint Family

Joint Family is an extended family arrangement prevalent among the Hindus of the Indian subcontinent, consisting of many generations living under the same roof.
All the male members are blood relatives and all the women are either mothers, wives, unmarried daughters, or widowed relatives, all bound by the common relationship. The joint family status being the result of birth, possession of joint cord that knits the members of the family together is not property but the relationship.

Six key aspects of Joint Family are :

• head of the family takes all decisions
• all members live under one roof
• share the same kitchen
• three generations living together (though often two or more brothers live together, or father and son live together or all the descendants of male live together)
• income and expenditure in a common pool, property held together.
• a common place of worship
• all decisions are made by the male head of the family.

Merits of a Joint Family:

The joint family is ideally suited for land-based rural families for its economic, social and psychological advantages. The joint operation of property allows increased efficiency of pooled labour and economies of a single kitchen and household. It provides for efficient geriatric and childcare, as there are many women to look after them.

This enables mothers to work in fields or do household work. Children grow up with care, love and affection from grandparents, uncles, aunts, cousins etc., besides their own parents. Joint family is an ideal setting to learn virtues of co-operation and collective living for the young people.

Family festivals and occasions can be celebrated more elegantly, enhancing the prestige of all the members. In general, joint family ensures the happiness and well-being of all its members.

Joint families may also own industries/business (besides agriculture). There are many well known industry/business houses running their enterprises jointly owned them by brothers etc., in a joint family.

Drawbacks:

The system is not without disadvantages though. Women in general have a low status and are often excluded from decision-making. There is little freedom for junior male members. The family, more based on tradition, may not be open to change or accepting new elements. The weight of the family is heavy on young couples. It hinders the process of individual freedom.

Self Assessment:

How well have I understood this unit?

Read and tick (✓) in the appropriate box.

A Letter to A Friend Summary in English

Ramesh and Suresh are friends. Ramesh lives in Hyderabad. Suresh came to Hyderabad on some personal work. He asked Ramesh to meet him at certain place but Ramesh could not meet him. For this Ramesh felt sorry and wrote this letter to Suresh.

In his letter, firstly, Ramesh apologised Suresh for not meeting him in his visit to Hyderabad. He remembered how they both played and spent their time happily with their families. He told Suresh about his busy and meaningless life. He told Suresh how he spent his time from morning to evening. He felt that his life in the apartment was just like a frog in a well.

He reminded Suresh many events of his childhood with him like playing games, going to swimming pool, doing all the work together in school, going on a picnic, celebrating Dasara and Depavali etc. He pitied his daughter who was always silent and spent all her time playing computer games in a very limited world.

He felt that he missed the real world in city life. He felt that he missed everybody and everything in his busy life. Finally he was happy that he had found time to write to Suresh and share his feelings.

Glossary:

apologize (v) : say sorry for doing something wrong
fairy tales (n) : stories about fairies and magic
warriors (n) : persons who fight in a battle or war
faded (adj) : less bright
hardly (adv) : almost no / almost not I almost none
disgusting (adj) : extremely unpleasant and unaccepted
gilli-danda (n) : karra (danda) – billa (gull) (in Telugu) / a rural sport of India
played with a short stick and a long stick.
apartment (n) : a set of rooms for living in, usually built in stairs
room (n) : empty space
unheeded (adj) : heard, seen or noticed but then ignored
appreciated (v) : recognised the good qualities
caring (v) : feeling that something is important
moment (n) : time/occasion

Telangana SCERT TS 8th Class Physics Study Material Pdf 8th Lesson Combustion, Fuels, and Flame Textbook Questions and Answers.

TS 8th Class Physics 8th Lesson Questions and Answers – Combustion, Fuels, and Flame

I. Reflections on Concepts

Question 1.
Give four examples of combustible materials.
Answer:
Some combustible materials are:

• Wood
• Paper
• Kerosene oil
• Straw
• Charcoal
• Match stick etc.

Question 2.
Why should not we store spirit or petrol near our living place’?
Answer:
Spirit or petrol is a ‘highly inflammable’ material. There will always be petrol vapour over the liquid petrol. The vapour is highly inflammable. These vapours can catch any type of flame and burn rapidly. So we should not store spirit or petrol near our living place.

Question 3.
The oil fires should not be sprayed with water. Why?
Answer:
Water is not suitable for fires involving oil and petroleum. :
Reason: Water is heavier than the oil. So water sinks below the oil and oil keeps burning on the top.

Question 4.
Water is not used to control fires involving electrical equipment. Why?
Answer:
If electrical equipment is on fire, water is not used to control fire. Because water may conduct electricity and harm those trying to douse the fire. (Note: ‘Douse’ means to put out the fire, by pouring water.)

Question 5.
List the ways adopted by firefighters to combat fires.
Answer:
To combat fires, firefighters follow one principle, which is the “Principle of elimination of factors which supports the combustion”.

The factors which support the combustion are:
a. Presence of a combustible material or the fuel.
b. Supply of air or oxygen.

c. High temperature.

1. The firefighters will put off the electric mains and then start spraying water on the fire.
   This water cools the combustible material. This prevents further spreading of the fire.
2. For fires involving oil and petrol. liquid carbon dioxide fire-extinguisher is used, CO₂, gas cools the combustible material. At the same time, it cuts off the

contact between the material and air (oxygen). Then the fire comes under control. This gas does not damage the material. So liquid CO₂ is an excellent fire – extinguisher.

Question 6.
Draw the diagram of a candle flame and label all the zones.
Answer:

Application of concepts

Question 1.
What precautions are to be taken while pouring water on fire?
Answer:

1. Water is not suitable for fires involving oil and petrol.
2. If electrical equipment is on fire, water may conduct electricity and harm those trying to douse the fire. So water cannot he used.

Question 2.
Give an example of a good fuel. How do you choose that fuel? Explain.
Answer:
For kitchen, it is LPG and for a motor car, it is CNG. These are some good fuels.
Reasons:

1. They are relatively cheap.
2. They bum easily in air at a moderate rate (not slow or explosive).
3. They produce a large amount of heat.
4. They do not leave behind undesirable substances.
5. They are easily available.

Question 3.
It is difficult to burn a heap of green leaves but not a heap of dry leaves. Explain why?
Answer:

1. It is easy to burn a heap of dry leaves because their ignition temperature is low.
2. It is difficult to burn a heap of green leaves because their ignition temperature is high. The green leaves contain water also. So the ignition temperature rises.

Question 4.
Where do you find spontaneous combustion and rapid combustion in your daily life?
Answer:
a) Spontaneous combustion: When we strike the head of a match stick over the side of a matchbox, it catches fire at once and Continues to bum. It is a case of ‘spontaneous combustion’.
b) Rapid combustion: We turn on the knob of the gas stove in the kitchen. Then we bring a lighted matchstick near it. The gas burns rapidly. It is a case of rapid combustion.

Question 5.
Why the fire brigade start the work by putting off the electric mains?
Answer:

1. Water conducts electricity. So it harms those trying to douse the fire, using water.
2. So the fire brigade starts work after putting off the electric mains.

Question 6.
Explain giving reasons: In which of the following situations water will get heated in a shorter time?
a) Srikar kept water beaker near the wick in the yellow part of a candle flame.
b) Sonu kept water beaker in the outer most part of the flame.
Answer:
Water gets heated in a short time, when the water beaker is kept in the outermost part of the flame.
Reason: A flame has three zones (or parts).

• The outermost part of the flame is faintly bluish in colour. Here, the gas undergoes complete combustion. So it is the hottest part of the flame.
• The middle part of the flame is yellow in colour. Here gas undergoes only partial combustion. So this part of the flame is not so hot. It is less hot than the outermost part of the flame.

Higher Order Thinking Questions

Question 1.
Why Phosphorus preserved in water?
Answer:
The inflammable (ignition) temperature of white (or yellow) phosphorus is 45°C. So when it is kept in air it easily catches fire and bursts into flames. So it is preserved in water.

Question 2.
How do you feel about “Fuels have become a part of human life”?
Answer:

1. A fuel is a source of energy. When a fuel burns, energy liberates.
2. This energy is utilised for various purposes to run automobiles, to operate generators, to run thermal power plants and a variety of industries, to run locomotives, etc.
3. All these play an important role in serving the human needs, by providing food, shelter, clothes, transportation and so on. So man depends on fuel, directly or indirectly. Hence it is said, ‘fuels have become a part of human life”.

Question 3.
Is there any other procedure to prove that oxygen is needed for burning?
Answer:
To prove that oxygen ¡s required for burning:
Material required: A pan of water, empty milk bottle, candle, a box of matches.
Instructions: Fix the candle on the pan of water, now light the candle.
Observation: The candle extinguishes and the water rises 1/4 of the milk bottle. We can put off fire by covering with sand or blanket because here we are preventing supply of oxygen from this we can prove that oxygen is needed for burning.

Question 4.
In a few years, the fuels on earth will be exhausted. Think, what would happen to human civilization?
Answer:
Fuel is a source of energy. The common fuels now in use are fossil fuels like coal, petrol, diesel oil, kerosene, natural gas, etc. Apart from these, wood is also used as fuel in some remote parts of rural areas. We know well, how these fuels are serving the man. From these fuels, we derive mainly the heat energy, thermal energy, mechanical energy, light energy etc.

The modern civilization lays its foundation of the applications on these different forms of energy. These fuels are non-renewable. Once exhausted, they cannot be replaced. In the absence of these traditional fuels, human life becomes miserable. Then, we have to go for alternate renewable sources of energy like tidal energy (from sea), wind energy, solar energy, gravitational energy. etc. These serve our purpose only to a very limited extent.

Multiple Choice Questions

Question 1.
The gas needed for combustion among the following [ ]
a) Argon
b) Oxygen
c) Carbon dioxide
d) Hydrogen
Answer:
b) Oxygen

Question 2.
The lowest temperature at which a substance catches fire is called its [ ]
a) Ignition temperature
b) Maximum temperature
c) Room temperature
d) Normal temperature
Answer:
a) Ignition temperature

Question 3.
The units of calorific value is [ ]
a) Newtons/grams
b) Newtons/Kg
c) Kilojoules/kg
d) Kilojoules/gram
Answer:
c) Kilojoules/kg

Question 4.
Spirit and petroleum turns into gas at [ ]
a) Room temperature
b) Ignition temperature
c) Maximum temperature
d) Normal temperature
Answer:
a) Room temperature

Question 5.
The type of combustion in which material suddenly burns into flames without the application of any external agent is called [ ]
a) Rapid combustion
b) Slow combustion
c) Spontaneous combustion
d) Explosion
Answer:
c) Spontaneous combustion

Suggested Experiments

Question 1.
Conduct an experiment for testing the necessity of air for burning.
Answer:
Experiment:

1. A small burning candle is put on a table.
2. A glass tumbler is inverted on it.
3. The candle continues to burn for a while, then begins to flicker and finally the flame goes off.
4. The tumbler is removed and the candle is again lighted. The tumbler is now put back over the candle.
5. When the candle flame begins to flicker and seems to be dying out, the tumbler is removed.
6. Then the candle continues again to burn.

We find that when we put the glass tumbler over the candle, supply of air is cut off. So the flame goes off. When the supply of air restored the candle again continues to burn. The experiment proves that we need air to burn a material.

Question 2.
Conduct an experiment to prove that Oxygen helps in burning.
Answer:
Aim: To prove that oxygen helps in burning.
Material required: Test tube, test tube holder, spirit lamp, matchbox, boom stick (agarbatti), potassium permanganate (KMnO₄)

Procedure:
1. A few crystals of potassium permanganate are taken in a test tube.
2. The test tube is heated carefully.
3. Potassium permanganate decomposes, liberating oxygen gas. The chemical decomposition is:

4. Insert the agarbatti with the burning stub into the test tube.
5. We will observe that stick will burn with a flame.

Question 3.
Can you heat water in a paper vessel’? How is it possible? Conduct an experiment to understand the Ignition temperature.
Answer:
Yes. We can heat water in a paper vessel.
Reason:

1. The heat supplied to the paper vessel gets transferred to water, by conduction of heat.
2. So, in the presence of water, the ignition temperature of the paper is not reached. Hence it does not burn. We can even boil water (say, 50 ml) if we take it in a small paper cup and heat with a candle.

Suggested Projects

Question 1.
List out the different fuels that are used in your daily life and classify them into solids, liquids, and gases.
Answer:
Domestic use: Wood, coal, coke, charcoal, kerosene, LPG, biogas. Automobiles! Aircraft! Trains/Rockets: Diesel oil, petrol, ethyl alcohol
Industry: Coal, charcoal, natural gas, biogas, diesel oil, coal gas, water gas, producer gas, oil gas, and semi-water gas.

Classification of fuels above fuels into solid, liquid, gases:

Solid	Liquid	Gases
Wood, coal, coke, charcoal, lignite	Kerosene, LPG, diesel oil, petrol, ethanol (Ethyl alcohol)	Biogas, natural gas coal gas, water gas, semi-water gas, producer gas, oil gas.

Question 2.
Collect information available on different fuels. Find out the cost per kg. Compare the cost with calorific value. Prepare report on that.
Answer:
It is observed that, as the calorific value of a fuel increased, its cost per kg also increased simultaneously.
Among the solid fuels, wood is cheaper than coal. Their calorific values are:
Wood (nearly 20,000 KJ / Kg)
Coal (nearly 29,000 KJ / Kg)
Among the liquid fuels, petrol, kerosene and diesel have almost the same
calorific values (45,000 KJ / Kg).
Among gaseous fuels, [PG has slightly more calorific value, than CNG.
(LPG = 55,000 KJ / Kg and CNG = 50,000 KJ / Kg)

Question 3.
Collect the information about annual fuel consumption in different parts of the world. How many years more the fossil fuels last? Make a poster with this information and
issue an appeal to save fuel.
Answer:
From a study of the statistical survey reports about the annual fuel consumption in different parts of the world, we arrive at the following conclusions.

• There is the highest consumption of fossil fuels in developed countries like America, Russia, Europe etc.
• The consumption of fossil fuel is comparatively less in underdeveloped countries like India, Pakistan, etc.,
• The consumption of fossil fuel by the undeveloped countries like South Africa is least.
  If the consumption of fossil fuels continues at the present rate, all the natural sources of the fuel get exhausted very soon. It may hardly take fifty or seventy years for the natural sources to drain.

TS 8th Class Physics 8th Lesson Combustion, Fuels and Flame Intext Questions

Think & Discuss

Question 1.
Why some materials burn and why some do not? Give reasons. (Text Page No: 109)
Answer:

1. Substances that vapourise on heating, burn.
2. Substances that do not vapourise on heating, do not burn.

Reason: it is the vapours of the substance that catch fire and burn, The solid or the liquid form of the substance does not catch fire.

Question 2.
Why some materials which do not burn at normal temperaturess burn at higher temperatures? (Text Page No: 109)
Answer:

1. Every material has an ignition temperature.
2. If the ignition temperature is low, the material burns at normal temperature.
3. If the ignition temperature is high, the material burns at a higher temperature.

Question 3.
If you lift the glass tumbler (Which Is placed over a burning candle) to 1cm height what happens? Why? (Text Page No :110)
Answer:
When we lift the glass tumbler to a certain height, air enters the tumbler from below. Then the candle continues to burn.
Reason: There is supply of air. So the candle continues to hum.

Question 4.
How do you say that the gas released in burning of KMnO₄ experiment is oxygen for burning? (Text Page No: 111)
Answer:

1. We know that oxygen is essential for combustion.
2. The burning stub of the agarbatti catches fire when inserted into the test tube. So there must be oxygen present in the test tube.

Question 5.
Can we replace KMnO₄ with any other substance to release oxygen?
Answer:
Yes, Oxygen can also be obtained by the following methods.
1. By hearing chlorates:

2. By heating metal oxides, Some metal oxides decompose on heating into the respective metal and oxygen.

Question 6.
Is there any other procedure to prove that oxygen ¡s needed for burning?
Answer:
To prove that oxygen is required for burning:
Material required: A pan of water, empty milk bottle, candle, a box of matches.
Instructions: Fix the candle on the pan of water, now light the candle.
Observation: The candle extinguishes and the water rises 1/4 of the milk bottle. We can put off fire by covering with sand or blanket because here we are preventing supply of oxygen from this we can prove that oxygen is needed for burning.

Question 7.
Why is phosphorus preserved in water? (Hint: Think about the role of Ignition temperature in combustion) (Text Page No: 113)
Answer:
The inflammable temperature of white (or yellow) phosphorus is 45’C So when it is kept in air it easily catches fire and bursts into flames. So it is preserved in water.

Question 8.
Why Kerosene stoves and Bunsen burners in your lab have small holes in them? (Hint: Think about the role of air) (Text Page No: 113)
Answer:

1. Air is required for the fuel to bum.
2. Air enters the stove or the burner through these small holes.
3. This air mixes with the fuel.
4. Then the fuel bums, if ignited.

Question 9.
A wax candle burns with a yellow flame. The domestic gas burns when lighted burns with a blue flame. Why? (Text Page No: 116)
Answer:

1. Yellow flame is produced due to the incomplete (or partial) combustion of wax.
2. Domestic gas (say, LPG) burns with a blue flame, due to the complete combustion of the petroleum gas.

TS 8th Class Physics 8th Lesson Combustion, Fuels, and Flame Activities

Activity – 1 :
(Do all materials burn?) (Text Page No: 108)

Question 1.
Describe an activity for testing different types of materials to determine whether they burn or not. What can we conclude from this activity?
Answer:
Using tongs, pick up a small piece of paper and bring it near to the lighted candle and keep it on flame as shown in the figure. Record your observations ma table.

Observations testing different types of materials to determine whether they burn or not.

Questions based on the above Activity -1
a. What do you observe in your attempt of burning water? (TexL P. No. 109)
Answer:
Water does not burn

b. Is there any difference in flame of lighted stick?
Answer:
From the above activity we can conclude that some materials burn and others dont. From the above activity we also observe that when we hum materials in air, heat and light are produced.

c. What happened to the lighted stick when it Is brought closer to water in the plate?
Answer:
The flame is put out.

d. What can we conclude from this activity?
Answer:
In the above activity -1 we observe that how the materials hum. Whether they burns immediately, slowly does not bum. In the above activity, we observed that when we burn material in air, heat and light are produced.

e. Which of the materials in the above activity are combustible?
Answer:
A piece of paper a piece of charcoal, magnesium ribbon, cool drink straw, cotton cloth, nylon cloth, dry wood, wax, plastic piece. petrol, natural gas and ether are combustible materials.

f. What is needed for the process of combustion?
Answer:
We need a matchstick or a lighter to hum a material.

Activity – 2: Testln the necessity of air for bimini (Text Page No: 110)

Question 2.
How will you prove that air is needed to a burn a material (or) Write an experiment for testing the necessity of air for burning.
Answer:
Experiment:

1. A small burning candle is put on a table. . .
2. A glass tumbler is Inverted on it.
3. The candle continues to burn for a while, then begins to flicker and finally, the flame goes off.
4. The tumbler is removed and the candle is again Lighted. The tumbler is now put back over the candle.
5. When the candle flame begins to flicker and seems to be dying out, the tumbler is removed.
6. 6. Then the candle continues again to hum. We find that when we put the glass tumbler over the candle, supply of air is cut off. So the flame goes off.

When the supply of air restored the candle again continues to burn, The experiment proves that we need air to burn a material.

Questions based on the above Activity – 2

a. Can we burn a material in the absence of air?
Answer:
No, we cant burn a material in the absence of air. Actually the oxygen that present in air supports the combustion of burning.

Activity – 3; Burning a paper with sun rays (Text Page No: 111)

Question 3.
Write how you can bum a paper with sun rays using a hand lens. (Magnifying lens)
Answer:

1. On a sunny day, if we focus the sun’s rays as a spot on a piece of paper using a hand lens, the paper first gets heated up at that spot.
2. After some time, smoke comes out and then the paper catches fire.
3. In this way we can burn a paper with sun rays.

Questions based on the above Activity – 3

a. Does a matchstick burn by itself? (Text Page No: Ill)
Answer:
No, a matchstick does not hum by itself.

b. Why do you rub the match stick on the side of the matchbox to burn it?
Answer:
A matchbox contains safety matches.

1. The sides of the matchbox (rubbing surfaces) contain a mixture of powdered glass and a little red phosphorus.
2. The head of the match stick contains a mixture of antimony trisulphide, Head of the safety (Sb₂S₃) and potassium chlorate (KClO₃).
3. When the match stick is struck against the rubbing surface, some red phosphorus converts into white phosphorus.
4. This reacts immediately with potassium chlorate in the matchstick head. Then heat is produced.
5. This heat ignites antimony trisulphide. Then combustion starts and it produces flame. The stick then catches fire and continues to burn.

c. Can you burn a piece of wood by bringing it near to a lighted matchstick?
Answer:
No. The lighted match stick does not produce sufficient heat, required to ignite the wood.

d. Why do we use paper or kerosene oil to start fire in wood or coal?
Answer:

1. The materials wood and coal are not easily combustible materials, They require high heat to catch fire. Their ignition temperatures are high.
2. Heat produced by a lighted match is not sufficient to ignite these materials.
3. A burning paper or kerosene produces the required heat, to ignite these materials.
4. So we use paper pieces or kerosene oil to start fire in wood or coal.

e. Can you make a list of some more inflammable substances? (Text P. No: 112)
Answer:
Some of the inflammable substances are:

1. Liquids: Petrol, alcohol, spirit, Liquified Petroleum Gas (LPG) and many organic liquids like benzene.
2. Gases: Compressed Natural Gas (CNG), Natural gas.

Activity -4:
Understandinf i2nitlon temoerature. (Text Page No: 112)

Question 4.
Take two small paper cups. Pour water in one of the cups. Put the two cups on different tripod stands and heat both of them using a candle.
Answer:

Questions based on the above Activity-4 (Text Page No: 112)
a. Which cup burns first?
Answer:
The empty cup burns first.

b. Does the water in the cup become hot? Why?
Answer:
Yes, The water in the cup becomes hot.
Reason: In this cup, heat is transferred to water, by conduction.

c. When does the second cup start burning?
Answer:
As long as there is water in the cup, the cup does not catch fire. So when all the water boils and vapourises away the graph cup catches fire.

Activity – 5: Observing the behaviour of different solid fuels: (Text PagNo; 115)

Question 5.
Explain an activity to observe the “Ignition Temperature.
Answer:
Ignition temperature:
The lowest temperature at which a substance catches fire is called its ignition temperature.

Activity:

1. Take two small paper cups. Pour water in one of the cups.
2. Put the two cups on different tripod stands and heat both of them using a candle.
3. The empty cups burns quickly. So its ignition temperature is less.
4. Though we supply head to both paper cups, but the heat in the second cup is transferred to water.
5. The presence of water in the second cup prevents the paper to reach its ignition temperature and hence it does not burn.

a. Describe the activity to observe the behaviour of different solid fuels.
Answer:

• Collect some fuels like candle, coat, charcoal, magnesium ribbon, wood. cakes of cow during. camphor, wick of the oil lamp, wick of kerosene stove, etc.
• Burn each of them one by one with the help of spirit lamp and note the time they take to catch fire.
• All of them do not burn in the same manner.
• Coal, charcoal, wood and cakes of cow-dung catch fire after a long time. They burn with slow fire. They do not produce flames.
• Magnesium ribbon catches fire slowly hut bums quickly with a dazzling light.
• Camphor, kerosene stove, wick of oil lamp and candle catch fire soon and burn producing a flame.

b. Do all they burn in same manner? If not what difference do you notice? (Text Page No: 115)
Answer:
1. All of them do not burn in the same manner.
2.

• Coal, charcoal, wood and cakes of cow-dung catch fire after a long time. They burn with slow fire. They do not produce flames.
• Magnesium ribbon catches fire slowly hut burns quickly with a dazzling light.
• Camphor. kerosene stove, wick of oil lamp and candle catch fire soon and burn producing a flame.

c. Do all of them form a flame while they are burning? (Text Page No: 115)
Answer:
No. Only some of the solid fuels form a flame and some do not form flame while they are burning.

d. Prepare a table, with fuels which form flame and which do not form flame on burning.
Answer:

Questions based on the above Activity (Text Page No: 112)

a. Which cup burns first?
Answer:
The empty cup burns first.

b. Does the water in the cup become hot? Why?
Answer:
Yes, the water in the cup becomes hot.
Reason: In this cup, heat is transferred to water, by conduction.

c. When does the second cup start burning?
Answer:
As long as there is water in the cup. the cup does not catch fire. So when all the water boils and vapourises away the empty cup catches fire.

Activity – 5 :
Observing the behaviour of different solid fuels: (Text Page No: 115)

Question 5.
Explain an activity to observe the “Ignition Temperature”.
Answer:
Ignition temperature:
The lowest temperature at which a substance catches fire is called its ignition temperature.

Activity:

1. Take two small paper cups. Pour water in one of the cups.
2. Put the two cups on different tripod stands and heat both of them using a candle.
3. The empty cups burns quickly. So its ignition temperature is less.
4. Though we supply head to both paper cups, but the heat in the second cup is transferred to water.
5. The presence of water in the second cup prevents the paper to reach its ignition
   temperature and hence it does not burn.

a. Describe the activity to observe the behaviour of different solid fuels.
Answer:

• Collect some fuels like candle, coat, charcoal, magnesium ribbon, wood. cakes of cow dung, camphor, wick of the oil lamp, wick of kerosene stove, etc.
• Burn each of them one by one with the help of a spirit lamp and note the time they take to catch fire.
• All of them do not burn in the same manner.
• Coal, charcoal, wood and cakes of cow-dung catch fire after a long time. They burn with slow fire. They do not produce flames.
• Magnesium ribbon catches fire slowly but bums quickly with a dazzling light.
• Camphor, kerosene stove, wick of oil lamp and candle catch fire soon and burn producing a flame.

b. Do all they burn in same manner? If not what difference do you notice? (Text Page No:115)
Answer:

1. All of them do not burn in the same manner,
2. a) Coal, charcoal, wood and cakes of cow-dung catch fire after a long time. They burn with slow fire. They do not produce flames.
   b) Magnesium ribbon catches fire slowly but bums quickly with a dazzling light.
   c) Camphor. kerosene stove, wick of oil lamp and candle catch fire soon and burn producing a flame.

c. Do all of them form a flame while they are burning? (Text Page No: 115)
Answer:
No. Only some of the solid fuels form a flame and some do not form flame while they are burning.

d. Prepare a table, with fuels which form flame and which do not form flame on burning.
Answer:

Activity – 6:
Observing the structure of the flame: (Text Page No: 116)

Question 6.
a. How many colours are there in a flame? “
Answer:
There are three zones in a candle flame.
1. Outermost zone of flame: Blue
2. Middle zone of flame: ‘Yellow
3. Innermost zone : Black

b. Starting from the base of the flame, how many flame zones do you observe?
Answer:
Starting from the case of the t lame, we observe two large zones – the yellow and the blue zones of the flame,

c. What is the colour of the outermost zone of flame?
Answer:
The outermost zone of the flame is blue in colour. It is the hottest part of the flame.

d. Observe the innermost zone of flame is dark. What do you observe?
Answer:
The innermost zone lying near the hase of the flame is dark.

Reason: Air cannot enter this region. So the wax vapours here, do not burn. Hence there is no light here. It is dark.

Activity -7:
Observing what happens in different zones of candle flame: (Text Page No:116)

Light a candle. Hold a glass tube with a pair of tongs and introduce its one end in the dark zone ola non, flickering candle flame. Keep lightened match stick nearby other ends of the glass tube. What do you observe?
a. Do you see a flame? :
Answer:
I do not see a flame.

b. If so what is it that produces a flame?
Answer:
When vapours of wax bum in air (oxygen), flame is produced. It is called, combustion.

c. Introduce a clean glass slide into the luminous zone of the flame when The candle’s flame is steady for 10 seconds. What do you observe?
Answer:
A blackish circular ring is observed on the glass slide.

d. A blackish circular ring is formed on the glass slide. What is it?
Answer:
It indicates the deposition of unburnt carbon particles present in the luminous zone of the flame. Incomplete combustion of wax takes place in this zone.

e. Hold a thin long copper wire just inside the flame for about half a minute. What do you observe?
Answer:

1. The copper wire just outside the flame gets red hot.
2. It indicates that the non-luminous zone of the flame has high temperature.

f. Why flames produce light?
Answer:
Light of a flame conìes from a process, called fluorescence or from incandescence’ of some particles.

Incandescence: When some substances are heated strongly to a very high temperature, the’ emit light. The process is called. incandescence. Eg: The tungsten filament in a filament bulb.

g. Why is fire hot?
Answer:

1. Fire is produced due to combustion of fuel.
2. Combustion is an oxidation reaction.
3. Oxidation reaction liberates heat. exothermic reaction). So fire (or flame) is hot.

h. Why caWt we fry food with water but of with oil?
Answer:

1. All food materials contain water. So to remove this water, food is to he heated beyond the boiling point of water (100°C).
2. If we use water to fry food, all this water vapourises away at 100°C. So water cannot be used to remove water present in the food material.
3. However, oil can be heated to more than 15OE’C, without charring the food (making it black). Oil is not vapourised at this temperature. So the food can he fried now.

Lab Activity – 1

Question 1.
How do you prove that oxygen helps for combustion? (Text Page No: 110 (Application to daily life, concern fo biodiversity)
Answer:
Aim: To prove that oxygen helps in burning.
Material required: Test tube, test Lube holder, spirit Lamp, matchbox, boom stick (agarbatti), potassium permanganate (KMnO₄)

Procedure:
1. A few crystals of potassium permanganate are taken in a test tube.
2. The test tube is heated carefully.
3. Potassium permanganate decomposes. liberating oxygen gas. The chemical decomposition is:

4. Insert the agarbatti with the burning stub into the test tube.
5. We will observe that stick will burn with a flame.

Question 2.
How does scented stick started burning?
Answer:
There is sufficient quantity of oxygen and heat in the test tube, to rekindle the burning stub of the agarbatti. So the agarbatti got fire.

Question 3.
Why does not it catch again fire when agarbatti (scented stick) is kept aside in air after putting its flame off?
Answer:
Though air contains oxygen.

1. The available oxygen is not sufficient to rekindle the burning stub of the scented stick.
2. The required temperature also is not available in air, to rekindle the burning stub.
3. The ‘ignition temperature is not reached’.
4. So the agarbatti does not catch again fire when it is kept aside in air after putting its flame off.

Telangana SCERT TS 8th Class Physics Study Material Pdf 7th Lesson Coal and Petroleum Textbook Questions and Answers.

TS 8th Class Physics 7th Lesson Questions and Answers – Coal and Petroleum Surfaces

Reflections on concepts

Question 1.
Explain why petroleum is also called as liquid gold?
Answer:
The substances which are obtained from petroleum are used in the manufacture of detergents, synthetic fibres etc., Due to its great commercial importance, petroleum is also called as ‘liquid gold”.

Question 2.
Name the petrochemical products which are used in agriculture industry.
Answer:
Plastic tubes, baskets, storing box, cultivation implement and fertilizers are the petrochemical products. which are used in agricultural industry.

Question 3.
Explain the process of formation of petroleum in Earth.
Answer:

1. Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay.
2. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum.

Question 4.
Why should people look for alternative sources of fossil fuel?
Answer:

1. Yes, alternative energy sources such as wind energy, solar energy can effectively replace fossil fuels.
2. These are completely emission-free.
3. This makes them extremely attractive from an environmental standpoint.
4. Alternative sources of energy will provide a hedge against rising fuel prices.

Question 5.
Draw the diagram of uses of coal and its products.
Answer:

Application of concepts

Question 1.
Name the petroleum products used for surfacing of roads.
Answer:
1. Earlier coal-tar a black, thick liquid which is obtained from coal processing and is a mixture of about 200 substances was mainly used for metalling or surfacing of the roads.
2. Now – a – days ‘bitumen’ which is a petroleum product, is used in place of coal – tar for surfacing the roads.

Question 2.
What will happen if fossil fuels like coal and petroleum are completely exhausted?
Answer:
1. If fossil fuels like coal and petroleum are completely exhausted, then various industries like thermal power, steel, generators, petrochemical industries etc would be closed.
2. Transportation system which is completely based on motor fuels like diesel, petrol, CNG would be stopped.
3. Most of the rural and urban people use fuels like kerosene and LPG for cooking. This would be mostly effected on basic needs.

Question 3.
Assume that you are a driver, what measures do you take to save petrol and diesel?
Answer:

1. I will check my vehicle tyres. Under inflation it can increase consumption of petrol or diesel.
2. Keep constant and steady speed as far as possible.
3. Switch off my vehicle engine in traffic jam.
4. Turn off the air conditioner whenever possible.
5. Plan my route mostly direct way.
6. Never stay in low gear. Get into higher gear as possible as ¡ can.
7. Maintain my vehicle engine regularly.
8. I will never keep foot on clutch. It leads to more fuel consumption.

Question 4.
Suggest some alternative ways to save the fuel resources.
Answer:

1. Use CNG as fuel for vehicles instead of petrol, diesel.
2. Walk, and cycle for short distances.
3. Use public transport instead of private vehicles.
4. Turn off the ignition, when we were in waiting at the signal for more than one minute.
5. Drive at speeds that optimize fuel consumption.

Question 5.
How do you appreciate the efforts of human beings to discover alternate energy sources to Coal and Petroleum for their daily use?
Answer:

1. Each person uses a good deal of energy in the form of fossil fuels like coal and petroleum.
2. Every day we bath, cook, clean, do laundry, drive and use products created from these fossil fuels.
3. Coal is an ancient gift serving modern society.
4. Due to the great commercial importance of petroleum, it is also called “black gold”.

Question 6.
Collect information about places where we get coal, petroleum and natural gas in India and mark the places on outline map of India.
Answer:

Higher Order Thinking Questions

Question 1.
How is biodiversity effected by the excessive use of fossil fuels?
Answer:

• Burning fuels releases carbon dioxide a greenhouse gas: which causes climate changes and leads to global warming.
• Coal-fired plants (industries) emits mercury, selenium, arsenic, lead in addition to greenhouse gases which are harmful to human health and environment.
• Many points from petroleum and heavy metals release toxic products into air. These toxic products cause various health problems including heart, lungs damage, nausea and dizziness.
• Because these toxic materials the survival of aquatic life, wildlife and birds life becomes more difficult which effects the biodiversity.

Question 2.
“Crude oil and refined fuel when spills into the sea from tanker of ships by accident”. Discuss the consequences of this on environment.
Answer:

1. Oil spills often result in both immediate and long-term environmental damage to natural ecosystem.
2. They damage beaches, mangrove forests and marine ecosystems.
3. They kill sea birds, marine mammals and shellfish.
4. It will also destroy wildlife habitats and breeding grounds.

Multiple Choice Questions

Question 1.
Which one of the following is less polluting fuel [ ]
a) Natural gas
b) coal gas
c) Kerosene
d) Petrol
Answer:
a) Natural gas

Question 2.
The main constituent of coal is [ ]
a) Carbon
b) Oxygen
c) Air
d) Water
Answer:
a) Carbon

Question 3.
Which one of the following materials is used for making shoe polish [ ]
a) Paraffin wax
b) Petrol
c) Diesel
d) Lubricating oil
Answer:
a) Paraffin wax

Question 4.
Which of the following is not a fossil fuel [ ]
a) Coal
b) Petroleum
c) Charcoal
d) Natural gas
Answer:
d) Natural gas

Question 5.
Which of the following is known as liquid gold [ ]
a) Kerosene
b) Diesel
c) Petroleum
d) Paraffin wax
Answer:
c) Petroleum

Suggested Experiments

Question 1.
Conduct an experiment to show that when we heat high-quality coal,a gas evolves which can burn.
Answer:
Aim: To show that when we heat high quality coal (carbon content is more) a gas evolves which can burn.

Material required: Two boiling test tubes, rubber cork, iron stands, delivery tube, jet tube, bunsen burner.

Procedure: Take a spoon of powdered coal and place it in a hard glass test tube and fix it to a stand as shown in the figure.

Close the open end of the test tube with a rubber cork and connect it to another test tube which is partially filled with water and has fixed to other stands, with the help of ‘U’ shaped delivery tube as shown in the figure. Heat the test tube strongly with the help of bunsen burner.

Test the gas evolved by the second test tube through the jet tube fixed to it, by bringing a lighted match stick near to its nozzle. You may notice that the brownish-black vapours evolve.

Suggested Projects

Question 1.
Burning fuels releases carbon dioxide, a greenhouse gas, which causes climate changes and leads to global warming. Collect information about this through newspapers, magazines etc. and prepare report.
Answer:
i. Most of the harmful effects ¿ire due to our carelessness. For example, crude oil and refined fuel spills from tanker ship accidents have damaged natural ecosystem. This can kill sea birds, mammals, shellfish and other organisms.

ii. Burning fuels release carbon dioxide, a greenhouse gas, which causes climate changes and leads to global warming.

iii. Coal-fired power plants emits mercury, selenium and arsenic which are harmful to human health and environment.

iv. Products from the coal and petrol can also harmful.

v. Many paints are petroleum based with some toxic substances added. Long after we finish painting, they release toxic products in air. This can cause a variety of health problems including heart and lung damage nausea and dizziness.

Report: Overuse of C.F.Cs causes global warming.

Question 2.
Compare a CNG-run vehicle with that of a diesel-run vehicle. What difference do you notice in both cases with respect to pollutants released, level of pollution and cost of fuel.

Name of the fuel	Cost of the fuel as on today	Pollutants liberated
Diesel/ Petrol
CNG

Answer:

Name of the fuel	Cost of the fuel as on today	Pollutants liberated
Diesel/Petrol	Diesel: ₹ 51.35 / Ltr Petrol: ₹ 73.73/Ltr	Carbon dioxide, carbon monoxide, nitrogen dioxide, hydrocarbons, particulate matter and lead.
CNG	CNG: ₹  40/ Kg	Negligible sulphur dioxide content does not contain lead, low nitrogen dioxide and particulate content, and low carbon monoxide content.

Report: C.N.G is less expensive and eco-friendly than other fuels.

Question 3.
Choose five families of your neighbourhood, collect the information about the measures that they adopt to conserve energy resources in transport and cooking.
Make a report on your observation

Name of the Head of the family	Number of members in family	No of vehicles using	Amount spent for Fuel in one month	Amount spent for the Cooking purpose

Answer:

Name of the family	Number of members in family	No of vehicles using	Amount spent for fuel in one month	Amount spent for cooking purpose
1. Prasad	4	1 (motorcycle)	₹ 850	₹ 380
2. Shyam	3	1 (motorcycle)	₹ 0	₹ 240
3. Sivaji	8	2 (motor cycle)	₹ 1675	₹ 550
4. Paul	7	1 (car-1) (motorcycle)	₹ 3400	₹ 500

Report: Cycle is less expensive, and eco-friendly compared to other vehicles.

TS 8th Class Physics 7th Lesson Coal and Petroleum Activities

Activity – 1:
IdentifvinE articles and materials used for various purposes (Text. P.No. 94)

Question 1.
Make a table as Column (A) gives the names of some activities’ arid items. Ask your grandparents or other older people and write down the names of the materials then used against the item given, in column B. In column C, write the names of materials being used at present. And also answer the following questions. (Information skills).
Answer:
Table

Articles/Activities (A)	Article/ Materials used 30-40 years ago (B)	Articles/ Materials used Today (C)
Containers for storing pickle	clay jars,…………..	plastic
Packing food for a journey	clothes, leaves	plastic tiffin
Water pipes in the house	metal pipes	PVC
Hair combs	wooden	plastic
Vessels for cooking food	copper vessels	steel utensils,………….
Fuels used to cook food	wood, coal	kerosene, LPG
Fuel used in a train engine	coal	diesel, …
Luggage for carrying clothes	metal trunks, …	plastic suitcase
Water buckets, pails	metal buckets	plastic buckets
Water storages in houses	metal containers (brass)	plastic buckets,…
Construction material	clay, limestone	cement, steel
Jewellery	metals like gold, silver,  diamonds	gold, silver, platinum, diamonds
Furniture (chairs, beds)	wood	plastic

Questions based on the above Activity – 1

Now think and write the answers: (Text. P. No. 94 & 95) (Information skills)

a. How many of these materials were available 10 years ago?
Answer:
Plastic, polythene, PVC pipes, LPG

b. How many of these materials were available 50 years ago? (Information skills)
Answer:
Steel utensils, petroleum products like kerosene and diesel etc.

c. How many of these materials were available 100 years ago? (Information skills)
Answer:
Clay jars, metals like iron, silver, gold, coal, wood, glass.

Activity- 2 :
List out the natural resources which are limited and which are abundant (Text. P. No.96)

Question 2.
Table (Concepl understanding/Project Work)

Resources Abundant
Resources Limited

Answer:
Resources Abundant air solar energy
Resources Limited coal petroleum minerals

Questions based on the above Activity- 2

a. What will happen if fossil fuels like coal and petroleum are completely exhausted? (Text. P. No. 97) (‘Making hypothesis/Conceptual understanding)
Answer:

1. If fossil fuels like coal and petroleum are completely exhausted, then various industries like thermal power, steel, generators, petrochemical industries etc would be closed.
2. Transportation system which is completely based on motor fuels like diesel, petrol, CNG would be stopped.
3. Most of the Rural and Urban people use fuels like kerosene and LPC for cooking. This would be mostly effected on basic needs.

b. What would be our future energy resources? (Text. P.No. 97) (Aesthetic sense/Bio – diversity /Conceptual understanding)
Answer:

1. Our country has enormous unconventional gas resources like coal bed methane, underground coal gas and gas hydrates. In the future, producing these unconventional gases. we would meet the energy demands.
2. Renewable energy sources Like solar energy, wind energy, biogas, biomass, hydrogen, ocean thermal energy would be our future energy sources.

c. Are the fossil fuel resources available plenty to meet the future energy needs? (Text. P.No. 97 (Conceptual understanding)
Answer:

1. No, the fossil fuels resources available to u are not sufficient to meet our future energy needs.
2. Due to supply is limited and increase of demand these fossil fuels would be more expensive in future.

d. What actions required to meet the future energy needs? (Text. P.No. 97) (Information skill! Conceptual understanding)
Answer:

1. First, we should conserve the fossil fuel resources as much as possible by reducing misuse.
2. To encourage and educate the people for usage of renewable energy sources like solar energy, wind power etc.

Activity – 3:
Identlfvhw various uses petroleum (Text. P. No. 100)

Question 3.
What are various uses of by-products of petrol?
Answer:
Uses of by-products of petroleum:

1. Pehol is used as motor fuel, aviation fuel and solvent for dry cleaning.
2. Kerosene is used as fuel for stoves, lamps and et aircrafts.
3. Diesel is used as fuel for heavy motor vehicles, electric generators etc.
4. Paraffin wax is used as ointment, candles and vaseline.

Activity -4:
Identifying uses of coal products (Text. P. No. 101)

Question 4.
Draw a flow chart showing varic.us uses of coal products. (Drawing)

a. What are the uses of coal products?
Answer:
The coal products are:

Coke	Coal Tar	Coal Gas
Manufacture of steel  Extraction of metals Manufacture of water gas and producer gas	In roads, synthetic dyes, pesticides, medicines explosives, paints, synthetic fibres, photographic metals, roofing materials, naphtalene, plastic, perfumes, insecticides	Fuel Lighting Cooking Heating

Activity 5:
Group discussion on misuse of fuel resources and its consequences (Text. P. No. 104)

Question 5.
Discuss in small groups how fuel resources are being misused in our daily life while doing various activities like… (information skills)
a) transport
b) cooking
c) use of electric appliance
Answer:
a) Transport:

1. Most of the people do not ensure correct vehicle tyre pressure.
2. Do not maintain engines regularly.
3. Lack of proper knowledge about fuel economy.

b) Cooking:

1. By using old conventional cooking vessels, not using pressure cookers.
2. Open vessel cooking.
3. Using so much of water while cooking.
4. Not proper regular checking regulator, pipes, burner for leaks.

c) Use of electrical appliances :

1. Using incandescent lamps instead of CFL
2. Using lights in day time, proper ventilation would be the solution.
3. Leaving electrical appliances on, when they were not in use,
4. Using conventional regulators.
5. Wet cloth ironing.
6. Use of drier in washing machine.

Questions based on the above Activity – 5

a. What are the consequences of misuse of fuels? Prepare a report. (Text. Pg. No. 104) (Applications to daily life)
Answer:

1. Misuse of fossil fuels releases a lot of pollutants into the atmosphere, which have various environmental effects.
2. Burning of so much Fuel also causes ozone depletion. This may result hazards like global warming.
3. A direct consequence is rising fuel costs. With rising demand and a limited supply, this is simply a matter of economics.

b. What methods could you suggest to prevent the misuse of fuels? (Text. P.No. 104)
Answer:
Suggestions to prevent the misuse of fuels:

1. More efficient engines and combustion systems.
2. Less intensive processing.
3. Heat and energy recovery and reuse.
4. Alternate delivery systems (mass transit rather than private vehicles.)
5. Improved energy conservation (insulation)

Lab Activity

Question 1.
Show that when high-quality coal is heated, a gas evolved which can burn. (Experimentation )(Text. Pg. No. 101)
Answer:
Aim: To show that when we heat high-quality coal (carbon content is more) a gas evolves which can burn.

Material required: Two boiling test tubes, rubber cork, iron stands, delivery tube, jet tube, bunsen burner.

Procedure: Take a spoon of powdered coal and place it in a hard glass test tube and fix it to a stand as shown in the figure.

Close the open end of the test tube with a rubber cork and connect it to another test
tube which is partially filled with water and has fixed to other stands, with the help of ‘U’ shaped delivery tube as shown in the figure. Heat the test tube strongly with the help of bunsen burner.

Test the gas evolved by the second test tube through the jet tube fixed to it, by bringing a lighted match stick near to its nozzle. You may notice that the brownish-black vapours evolve.

The above vapours passed through water contained in a test tube. Colourless gas bubbles come from the water. 1f you burn the gas that is evolving through the jet tube. You can witness a bright flame at the nozzle. From this we conclude that when we heat high-quality coal, a gas evolves which can burn.

a. Repeat the above experiment if we replace lime water, soapy water instead of water used in second boiling. What do you observe? Give reasons for the changes you observed in two experiments. (Experimentation & F.I.) (Text. Pg. No. 102)
Answer:

1. By replacing lime water instead of water used in the second test tube, after heating the first test tube carbon dioxide gas is evolved and it turns lime water into milky.
2. By replacing soap water instead of water used in the second test tube, after heating the first test tube carbon dioxide gas is evolved and it forms a precipitate.
3. This is because of carbon dioxide gas is acidic in nature.

b. What inference can you draw from these experiments? (Text. P.No. 102) (Experimentation & F.I.)
Answer:
Inference: When coal is heated in the first test tube since the coal mainly contains carbon. It emits carbon dioxide gas. Due to acidic nature of carbon dioxide gas, it turns lime water into milky and forms precipitate with soap water.

TS Board Telangana SCERT Class 8 Physics Solutions 6th Lesson Reflection of Light at Plane Surfaces Textbook Questions and Answers.

TS 8th Class Physics 6th Lesson Questions and Answers – Reflection of Light at Plane Surfaces

I. Reflections on concepts.

Question 1.
If a ray incidents normally on a plane mirror, what will be the angle of reflection?
Answer:
When the incident ray comes along normal it
bounces back in same direction
Here i = 0
r=0
where i → Angle of incidence
r → Angle of reflection

Question 2.
Explain the laws of reflection’?
Answer:
Laws of reflection:
1st Law: The angle of incidence is equal to the angle of reflection.
2nd Law: The incident ray, the normal, and the reflected ray lie in the same plane.

Question 3.
Explain the process of formation of an image with a pinhole camera? Draw a ray diagram to show this.
Answer:

1. The light from the candle travels straight in all directions from each point of the flame of the candle.
2. But only the light coming in some particular direction can enter into the camera through its pinhole.
3. Light which comes from the point at the bottom of the flame goes straight towards the top of the screen.
4. In this way the light coming in a particular direction from each point of the flame will be able to enter into the pinhole and light going in other direction is blocked by the black sheet.
5. This leads to the formation of inverted image on the screen.

Question 4.
Why does the image in plane mirror suffers lateral inversion?
Answer:

1. Take an object before a plane mirror.
2. The light rays which come from right side of the object reach the plane mirror.
3. The reflected ray reaches our eye.
4. But our brains feels that the ray is coming from the inside of the mirror.
5. That is why the right side of the object looks like left side in the image.

Question 5.
Draw a ray diagram to understand the formation of image for a pointed object by a plane mirror’? Explain it.
Answer:
‘O’ is a point object. Some rays from ‘O’ reach the mirror and get reflected.
When we look into the mirror, the reflected rays seem to be coming from the point I.
So point I is the image of point object O’.

II. Application of concepts

Question 1.
In the adjacent figure, AO and OB are incident and 90° reflected rays respectively. ∠AOB = 90°. Find the values of angle of incidence and angle of reflection?

Answer:

To find the angle of incidence and angle of reflection we should draw a normal at
the point of Indicence “O”. It bisects 90° into 45° and 45°. N
∴Angle of incidence “i” = 45
Angle of reflection “r” = 45

Question 2.
Bharath stands in front of a plane mirror at a distance of 5m. from the mirror and observes his image in the mirror. If he moves 2m. towards the plane mirror, then what will be the distance between Bharath and his image?
Answer:
The distance of Bharath and mirror, in the beginning, is 5m Now he walks 2 m towards the mirror.
Then he is at a distance 3m from the mirror (∵ 5 – 2 = 3 m)
Then the image distance behind the mirror is also 3 m.
The distance between Bharath and his image in the mirror is 3 + 3 = 6m
If we take sign convention into consideration it is 3 – 3 = O

Question 3.
Explain diagrammatically the image of letter ‘B’ in a plane mirror.
Answer:

Question 4.
Why can’t we see our image in a white sheet of paper though it reflects light?
Answer:

1. Reflection of light takes place on every’ opaque substance.
2. In case of white paper sheet, it reflects light only.
3. You can form image on a paper with the directions of light rays.
4. That image is only drawn on paper sheet.
5. It is neither real nor virtual.
6. So, we cannot see the image there
7. Whereas the image formed by a plane mirror is virtual.
8. So, we cannot see the image on white paper though it reflects light.

Question 5.
Discuss the merits and demerits of using mirrors in building elevation?
Answer:
Merits:

• Mirrors can be cut into different shapes or sizes.
• Mirrors do not rust.
• Mirrors do not let water to pass through them.

Demerits:

• Elevation with mirrors is very expensive.
• Mirrors break very easily.
• Mirrors may melt at high temperatures.

III. Heigher Order Thinking Questions.

Question 1.
Observe the adjacent figure. AB and BC are two plane mirrors arranged at 1200. A ray incident at and angle 550 on AB. Find the value of ’x’?

Answer:

Here given ∠PQN₁ =‘55° (angle of incidence) ∴ ∠ N₁QR = 55° (angle of reflection)
∴ Glancing angles ∠AQP = 90° – 55 = 35° ∠RQB = 35°
Now in Δle QBR = ∠Q+ ∠B + ∠R =180°
∴ Second angle of incidence is 90° – 25° = 65°
∴ 35+120 =∠R = 180°⇒ ∠R = 25°
Since angle of incidence is equal to angle of reflection, we can say x = 65° and we can also ∠SRC = 90° – 65° = 25°

Question 2.
Niharika holds a clock in her hand, which shows the time 3’o clock. If she observes the clock in a plane mirror, what will be the time that the clock show In the plane mirror?
Answer:
If the time in clock = x
The formula for the time in the plane mirror = 12- x
∴ 3’ o clock in her wristwatch is nothing but 12 – x = 9’ o clock in the mirror.

Question 3.
Two plane mirrors are fixed at right angles to each other and an object is placed between them as shown in the figure. Trace the path of the rays by which an observer A
see the final image in one of the mirrors.

Answer:

Question 4.
Two divergent rays originating from the same point have an angle of 10°. between them. If they strike a plane mirror with same Incident angles, what will be the angles of reflection?
Answer:

Here if we draw normals at the point of incidence we can find angles of incidence and reflection.
Here OA and N₁N¹₁ are parallel.
∴ OP is transversal line
∴ Angle of incidence = 5° and angle of reflection = 25°.

Multiple choice questions

Question 1.
Angle of incidence Angle of reflection. This rule is explained by …………………. principle. [ ]
(A) Format
(B) Newton
(C) Archimedes
(D) Pascal
Answer:
(A) Format

Question 2.
Which of the following letters doesn’t suíler lateral inversion. [ ]
(A) C
(B) O
(C) B
(D) N
Answer:
(B) O

Question 3.
A ray of light incidents on a plane mirror at an angle of 90° to its surface. What will be the angle of reflection? [ ]
(A) 0°
(B) 90°
(C) 45°
(D) 180°
Answer:
(A) 0°

Question 4.
If we move an object away from the plane mirror the size of images seems to be [ ]
(A) Increases
(B) decreased
(C) of the same size
(D) Image can’t be seen
Answer:
(B) decreased

Question 5.
Which of the following is incorrect with respect to the image in a plane mirror? [ ]
(A) Image is erect
(B) Size of the image is same as the size of object
(C) Laterally Inverted
(D) Image is real
Answer:
(B) Size of the image is same as the size of object
(C) Laterally Inverted

Suggested Experiments

Question 1.
Verify laws of reflection experimentally.
Answer:
Aim: Verification of 1st law of reflection.
Required material: Mirror strip, drawing board, plane mirror, pins, clamps, scale, and pencil.

Procedure:

• Take a drawing board and fix a plane mirror on it with the help of clamps.
• Draw a straight line AB along the mirror and also a normal (ON) to AB at the point ‘O’.
• Draw a straight line PQ making certain angle (i) with ON as shown.
• Fix two pins the point P and Q on the paper vertically.
• Observe the image P¹ of the pin P and Q¹ of the pin Q, in the mirror kept along the line AB.
• Fix two more pins R and S such that they are in the same line as that P¹ and Q¹.
• Join R, S, and O as shown.

Observation: The angle between RS and ON is almost same as that of PQ and ON i.e. the angle of incidence = angle of reflection. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.

Conclusion: In all observations, the angle of incidence is equal to the angle of reflection. Hence first law of reflection is verified.

ii) Aim: Verification of 2nd law of reflection.
Required material: Mirror strip, drawing board, plane mirror, pins, clamps, scale, and pencil.

Procedure:

• Take a drawing board and fix the plane mirror on it with the help of clamps.
• Draw a straight line AB along the mirror and also a normal (ON) to AB at the point ‘O’.
• Draw a straight line PQ making certain angle (1) with ON as shown.
• The incident ray is the ray which is passing through the points “P” and “Q” touching the paper.
• The reflected ray is the ray which is passing through the points “R” and “S” touch the same paper and ON is the normal to the mirror point O.

Observation: The incident ray and reflected ray are in the plane parallel to the plane of the paper. Repeat the experiment with different angles of incidence.

Conclusion: In all observations incident ray and reflected ray and normal are lie in the same plane. Hence 2nd’ law of reflection is verified.

Question 2.
Find the plane of reflection experimentally for the incident ray which passes through
the heads of the pins pierced in front of the mirror as shown in figure 8.
Answer:
Aim: To find the plane of reflection for the incident ray which is passed through head of pins pierced infront of mirror.
Required material: Mirror strip, drawing board, a plane mirror, pins, clamps, scale and pencil.

Procedure:

• Take a drawing board and fix a plane mirror on it with the help of clamps.
• Draw a straight line AB along the mirror and also a normal (ON) point ‘O’.
• Draw a straight line PQ making certain angle (i) with ON as shown.
• Fix two pins at the point of P and Q vertically.
• The incident ray is the ray which is passing through the points “P” and “Q” touching the mirror the reflected ray is the ray which is passing through the points “R” and “S” touching the same mirror and ON is normal to the mirror point at point ‘O’.
• The heads of all pins pierced at points P, Q, R, and S in this experiment are in the same height.

Observation: The incident ray is the ray which is passing through the heads of pins those are located at points P and Q and reflected ray is the ray which is passing through the heads of pins those are located at points R and S. The plane in which the incident ray and reflected ray and normal will lie in the plane of reflection.

Suggested Project Works

Question 1.
Make a solar heater! cooker with plane mirrors and write a report on the process of making.
Answer:

• Make a wooden or iron frame in the shape of a TV dish.
• Take acrylic mirror sheet and cut it into 8 or 12 pieces in the shape of triangles with a
  height equal to the radius of TV dish.
• The bases of the triangles together make the circumference of the dish.
• Stick the triangle mirror sheets to the dish.
• This act as solar cooker/heater.
• Arrange this solar cooker so that concave part faces the Sun.
• Find its focal point and place a vessel at that point.
• It will get heated. We can even cook rice in that vessel.

Question 2.
Generally, periscopes are made in the shape of “Z” make your own periscope in the shape of” C”. Discuss the problems faced while using the periscope you made in shape “C”. Draw the ray diagram to explain the formation of image in shaped periscope.
Answer:

1. Periscope works on the principle of reflection.
2. When it is in “Z” shape the light rays get reflected at the corners twice and final light ray emerges easily.
3. If it is taken in ‘C’ shape; the reflected light would not go in some other direction.
4. The purpose of periscope is to view the images of objects secretly.
5. If you take it in ‘Z’ shape we can see the changes of the objects which cannot be seen directly.

TS 8th Class Physics 6th Lesson Reflection of Light at Plane Surfaces Intext Questions

Think and Discuss

Question 1.
In a pinhole camera experiment does the explanation match your observation? (Text. P.No. 85)
Answer:
Yes, the pinhole camera forms a real, inverted and diminished image, if the object is far away.

Question 2.
What happens ¡f the hole ¡s much bigger i.e. equal to the size of the flame?
Answer:
If the size of the hole is equal to size of the flame, no image is formed on the screen due to the overlapping of light rays from different parts of the object.

Question 3.
If so, can we get an image of a flame on the screen of the pinhole camera? Why?
Answer:
We can get the image of the flame in a pinhole camera provided the hole is small enough.

Question 4.
What happens if we observe the same flame with the same pinhole camera from a long distance?
Answer:
The size of the image depends on its distance. So, we see a smaller image if it is observed from a longer distance.

TS 8th Class Physics 6th Lesson Reflection of Light at Plane Surfaces Activities

Activity-1:

Question 1.
Describe an activity to explain the process of formation of image by a pinhole camera. (Text. P.No. 84)
Answer:
Refer Q.No. 3 in ‘Reflections on concepts.

Activity-2: (Text. P.No. 85)

Question 2.
What is the Fermat principle? Prove it by a small activity.
Answer:

• A smart crow is on a tree at point ‘A’ as shown in figure-1. Some grains are on the ground.
• If the crow wants to take a grain and reach the point ‘Won the other tree as early as possible (in the least time)
• The crow can pick the grain from any point on the ground but the condition is; selecting a point on the ground to reach point ‘B’ from points A in the least possible time.
• If we assume that the speed of the crow is constant the path that the crow selects should be the shortest.

By observing all figures, path AEB is the shortest path to reach point B from A. It would take the least time. So the smart crow will pick the grain from point E. If we draw a normal EE1 at point E, we can easily find the angle AEE’ is equal to angle EEB. Light also selects the path which takes the least time to travel. This is the Fermat principle.

Activity-3:

Question 3.
Check your understanding of reflection. (Text. P.No. 87)
Answer:

1. Look at the figures (1) and (2).
2. Let us suppose that have been given a plane mirror strip.
3. We can observe figure (2) from (1) by placing the plane mirror in such a manner we can see in figure (3).

Lab Activity

Question 1.
Verify the laws of reflection through an activity. (Text. P.No. 87)
Answer:
Aim: Verification of V law of reflection.
Required material: Mirror strip, drawing board, plane mirror, pins, clamps, scale, and pencil.

Procedure:

1. Take a drawing board and fix a plane mirror on it with the help of clamps.
2. Draw a straight line AB along the mirror and N also a normal (ON) to AB at the point ‘O’.
3. Draw a straight line PQ making certain angle (i) with ON as shown.
4. Fix two pins the point P and Q on the paper vertically.
5. Observe the image P¹ of the pin P and Q¹ of the pin Q, in the mirror kept along the line AB.
6. Fix two more pins R and S such that they are in the same line as that P¹ and Q¹.
7. Join R, S and O as shown.

Observation: The angle between RS and ON is almost same as that of PQ and ON i.e. the angle of incidence = angle of reflection. Repeat the experiment with different angles of incidence and measure the corresponding angles of reflection.

Conclusion: In all observations, the angle of incidence is equal to the angle of reflection. Hence first law of reflection is verified.

Question 2.
How do you verify the 2nd law of reflection of light with an experiment?
Answer:
Aim: Verification of 2nd law of reflection.
Required material: Mirror strip, drawing hoard, plane mirror, pins, clamps, scale, and pencil.

Procedure:

• Take a drawing board and fix the plane mirror on it with the help of clamps.
• Draw a straight line AB along the mirror and also a normal (ON) to AB at the point ‘O’.
• Draw a straight line PQ making certain angle (i) with ON as shown.
• The incident ray is the ray which is passing through the points “P” and “Q” touching the paper.
• The reflected ray is the ray’ which is passing through the points “R” and “S” touch the same paper and ON is the normal to the mirror point O.

Observation: The incident ray and reflected ray are in the plane parallel to the plane of the paper. Repeat the experiment with different angles of incidence.

Conclusion: In all observations incident ray and reflected ras’ and normal are lie in the same plane. Hence 2nd law of reflection is verified.

Problems

Question 1.
if the radius of curvature of a spherical mirror is 20cm, what is its focal length?
Solution:
Radius of the curvature R = 20 cm
We know that focal length
f = \(\frac{\mathrm{R}}{2}=\frac{20}{2}\) cm
∴ f = 10 cm
Thus, the focal length of this spherical mirror is 10 cm.

Question 2.
Find the size, nature and position of image formed when an object of size 1 cm is placed at a distance of 15 cm from a concave mirror of focal length 10 cm.
Solution:
Position of image:
Object distance u = —15 cm (To the left to mirror)
Focal length f = – 10 cm (it is concave mirror)
image distance v = ?
We know that \(\frac{1}{\mathrm{f}}=\frac{1}{\mathrm{u}}+\frac{1}{\mathrm{v}} \)
⇒ \(\frac{1}{\mathrm{v}}=\frac{1}{\mathrm{f}}-\frac{1}{\mathrm{u}}=\frac{1}{-10}-\frac{1}{-15}\)
= \(\frac{-1}{10}+\frac{1}{15}=\frac{-3+2}{30}=\frac{-1}{30}\)
∴ v = -30
Thus, the position of image is 30cm to the left side of mirror.

Nature of image: Since the image is formed in front of the concave mirror, it will be real and inverted,

Size of image:
Magnification, m = \(-\frac{\mathrm{v}}{\mathrm{u}} \)
v = -30 cm
u = -15 cm
m = \(-\left(\frac{30}{15}\right)\)

We know that magnification m = \(\frac{\mathrm{h}_2}{\mathrm{~h}_1}\)
Where h₁ = height of the object = 1 cm
h₂ = height of the image =?
m = -2,then
h₂ = m × h<sub<1
= -2 × 1 cm
∴ h₂ = -2 cm
Thus the size of the image is 2 cm long. So magnified image is formed.

Question 3.
A concave mirror produces three times magnified real image of an object placed at 10 cm in front of it. Where is the image located?
Solution:
Magnification m = -3 (image is real)
Object distance u = – 10 cm (To the left of mirror)
Image distance v =?
We know m = \(-\frac{v}{u} \)
⇒ v = m × -u
= -3 × (-10)
= -3 × 10
∴ v = -30 cm
Thus, the image is located at a distance of 30 cm in front of the mirror.

Question 4.
An object is placed at a distance of 2m from a plane mirror. Find the image distance and magnification produced.
Solution:
Object distance: u = 2m
Mirror formula: \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)
For a plane mirror: f is an infinity
\(\frac{1}{v}+\frac{1}{u}=\frac{1}{\infty}\) = 0
\(\frac{1}{\mathrm{v}}=\frac{1}{\mathrm{u}} \)
⇐ v = -u
– ve symbol indicates the image is formed behind (in) the mirror.
So, image distance: v = 2m
Linear magnifkation : m = \(\frac{\dot{\mathrm{v}}}{\mathrm{u}}=\frac{2}{2} \) = 1
So, a plane mirror does not magnify the image.

Question 5.
An image Is formed at a distance of 10 cm from the pole of a convex mirror of focal length 20 cm. Find the position of the object.
Solution:
Image distance: v = 10cm
Focal length : f = 20cm
Object distance: u =?
sign convention
u – ve; v + ve, +ve
Mirror formula:
\(\frac{1}{\mathrm{u}}=\frac{1}{\mathrm{f}}-\frac{1}{\mathrm{v}}\)
= \(\frac{1}{20}-\frac{1}{10}\)
\(\frac{1}{u}=\frac{1-2}{20}=\frac{-1}{20}\)
u = 20
∴ Obfrct is placed 20cm before the mirror,

Question 6.
The focal length of a spherical minor is 25cm. What is its radius of curvature?
Solution:
Focal length of the mirror: f = 25cm
Radius of curvature: R = 2f
= 2 × 25 = 50cm
R = 50cm

Question 7.
Where should an object be placed to obtain the image at same position for a concave mirror of radius of curvature 40cm?
Solution:
Focal length:
f = \(\frac{\mathrm{R}}{2}=\frac{40}{2}\)= 20 cm
\(\frac{1}{\mathrm{f}}=\frac{1}{\mathrm{v}}+\frac{1}{\mathrm{u}}\)
Object distance :
\(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}=\frac{2}{u} \)
u = v
u = 2f
= 2 × 20 = 40 cm

∴ An object should be placed at 40 cm

Question 8.
An object of height 1 cm is placed in front of a concave mirror of focal length 10 cm, such that a virtual image is formed. If the height of the image is 3 cm, find the object
distance.
Solution:
Height of the object; h₀ = 1 cm
Height of the image: h_i = 3cm
Magnification = \(\frac{\mathrm{v}}{\mathrm{u}}\)
\(\frac{\mathrm{v}}{\mathrm{u}}\) = 3 ⇒ v = 3u
Magnification : m = \(\frac{\mathrm{h}_{\mathrm{i}}}{\mathrm{h}_0}=\frac{3}{1} \) = 3
Focal length of the mirror: f = 10cm
Mirror formula; \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f} \)
Sign convention : u – ve; f-ve; v + ve
\(\frac{1}{\mathrm{v}}-\frac{1}{\mathrm{u}}=-\frac{1}{\mathrm{f}} ; \frac{1}{\mathrm{u}}=\frac{1}{\mathrm{v}}+\frac{1}{\mathrm{f}}\)
\(\frac{1}{u}=\frac{1}{3 u}+\frac{1}{f} \)
\(\frac{1}{10}=\frac{1}{u}-\frac{1}{3 u}=\frac{3-1}{3 u}=\frac{2}{3 u}\)
3u=20u ⇒ u = \(\frac{20}{3}\) = 6.67cm

Question 9.
What is the range of object distances for the formation of diminished image, by a concave mirror of focal length 30cm?
Solution:
A diminished image is formed by a concave mirror when the object is placed between infinity and center of curvature.
So, the range is infinity to 2f
R = infinity to 2f
Range: ∝ to 60 cm

Telangana SCERT 8th Class English Guide Telangana State Unit 1B My Mother (Poem) Textbook Questions and Answers.

TS 8th Class English Guide Unit 1B My Mother (Poem)

I cannot remember my mother,
only sometime in the midst of my play
a tune seems to hover over my playthings,
the tune of some song that she used
to hum while rocking my cradle.

I cannot remember my mother,
but when in the early autumn morning
the smell of the shiuli flowers floats in the air,
the scent of the morning service in the temple
comes to me as the scent of my mother.

I cannot remember my mother,
only when from my bedroom window I send my
eyes into the blue of the distant sky,
I feel that the stillness of my mother’s gaze
on my face has spread all over the sky.

Questions and Answers:

Answer the following questions.

Question 1.
How does the poet feel the presence of his mother?
Answer:
The poet feels the presence of his mother in his playthings when he touches them. He feels her presence in his humming of a song and in the smell of the shiuli flowers offered to god in the morning puja in the temple. He feels the stillness of his mother’s gaze when he looks at the sky on a clear day.

Question 2.
What do you understand from the statement – 7 cannot remember my mother’ ?
Answer:
The poet says that he cannot remember his mother. This means that he expresses his inability to actually recall the face or the features of his mother.

Question 3.
Does the poem express sadness? If yes, pick out the suggestive expressions.
Answer:
The poem expresses a note of sadness and nostalgia as the poet cannot recall the face or the features of his mother. The first line in every stanza ‘I cannot remember my mother’ suggests this.

Question 4.
What imagery do you find in each stanza? To which sense does it appeal to you?

Answer:

Stanza	Images	Sense it appeals to
1	Mother rocking the cradle and singing a song	ears
2	The smell of shiuli flowers The scent of morning service in the temple The scent of his mother	nose
3	The blue of the distant sky	eyes

Question 5.
Read the poem ‘My Mother’ again to complete the table.

Answer:

Questions	Stanza – 1	Stanza – 2	Stanza – 3
Who are the persons involved?	The poet and his mother	The poet and his mother	The poe and his mother
Where does the action take place?	At play	In the temple	In the poet’s bedroom
What is the mother associated with?	The tune of a song hummed by his mother	The scent of the shiuli flowers in the temple	The blue of the distant sky
What is the theme?	The poet feels the presence of his mother in the tune of a song.	The poet feels the presence of his mother in the fragrance of the shiuli flowers in the temple.	The poet feels the presence of his mother in the blue of the sky.

Question 6.
We all love our mother, don’t we? We love her because of certain qualities. Think and write about her qualities.
Answer:
The definition of a mother is a woman who takes on the selfless and unconditional responsibility to nurture the emotional and physical well-being of her kids. We all love our mothers because of their great qualities. She offers unlimited love and affection. She sees things from the kids point of view. She is generous and caring. She shows patience and has empathy. She is unselfish.

Question 7.
How would you choreograph the first stanza? (Group work)
a) What settings do you arrange ?
b) What are the characters and their actions ?
c) What is the sequence of actions ?

Answer:
a) Play time, puja time and bed time are the three main settings.
b) The poet and his mother are the main characters.
c) Feeling the presence of the mother at play time, at puja time and bed time are the sequence of actions.

Stanza	Action of the main character (s)	Action of the supporting characters
1	The poet feels the presence of his mother while he was playing.	The supporting team/characters sing a tune rocking the cradle.
2	The poet feels the presence of his mother when he smells the scent of the shiuli flowers.	The supporting team/characters offer the shiuli flowers to God.
3	The poet stands at the window of his bed room and looks into the blue of the distant sky.	The mother character appears as she is looking down at him lovingly.

Each group may choreograph different stanzas of the poem.

My Mother (Poem) Summary in English

‘I Cannot Remember My Mother’ is a gentle nostalgic poem written by Rabindranath Tagore.

Tagore’s mother passed away when he was young. In this poem, he expresses his inability to actually recall the face or the features of his mother. The sight of his playthings reminds the j poet of a tune hummed by his mother. This tune reminds him of her. But often a smell or a tune triggered off in him reminds him the happy moments that he shared with his mother. Memory and nostalgia become the best elements of his imagery.

When he looks at his playthings he seems to be able to hear a tune, a lullaby that would be sung perhaps as she rocked her baby to sleep. Tagore also recalls this tune as he touches his old toys.

In autumn, the shiuli trees in Bengal blossom into fragrant tiny flowers which are used for worship. His mother would string the flowers for the morning puja at the temple. So powerful was the fragrance of the shiuli flowers that they would trigger off happy memories of his mother.

Tagore also recalls the quiet serene gaze of his mother when he looks at the vast expanse of the clear blue sky :
Simplicity and eloquence reveal the deep rooted emotional bonding that the poet had j with his mother. It makes us realise the great impact her quiet dignity had on the poet even at that tender age. This poem also has a very’ soft and evocative feminine mystique. Nothing loud, nothing stark, only soothing suggestions of a mother’s memory hinged on fragrance and the morning puja or the old melody.

About the Poet:

Rabindranath Tagore (1861-1941) is popularly known as Vishwa Kavi and Gurudev. He was the founder of Shantiniketan, an experimental school. He was awarded the Nobel Prize in literature for his ‘Gitanjali’, the Song of Offerings. Each of his poems reflects Indian vision and love towards his Mother Land. He is considered the Voice of Indian Heritage and Spiritualism.

Glossary:

midst (n) : the middle part of something/ while something is happening
hover (v) : remain in the air
hum (v) : sing a tune with lips closed
rocking (v) : moving gently backward and forward
cradle (n) : a small bed for a baby which can be pushed gently from side to side
shiuli (n) : small, white or orange flowers that bloom in autumn (chamomile in English)
float (v) : move slowly
scent (n) : pleasant smell / perfume / good smell
distant (adj) : far away in space or time
stillness (n) : the quality of being quiet and not moving
gaze (n) : look steadily at something or somebody

TS Board Telangana SCERT Class 8 Physics Solutions 5th Lesson Metals and Non-Metals Textbook Questions and Answers.

TS 8th Class Physics 5th Lesson Questions and Answers – Metals and Non-Metals

Reflections on concepts

Question 1.
How can you explain that sound has energy.
Answer:

1. Take a cell phone in a plastic bottle.
2. Cover the plastic bottle with stretched rubber balloon.
3. Keep some sugar granules or sand on the balloon.
4. When the cell phone in side is not playing songs the sand parficles on the diaphragm remains stationary.
5. When the cell phone plays songs we can observe the vibration of the diaphragm where sand particles dancing is also observed.
6. So we can conclude the sound produced inside the bottle is responsible for these vibrations. Thus sound has energy.

Question 2.
Write the unit to measure the sound intensity.
Answer:
The intensity of sound is measured in dB (decibles).

Question 3.
Write the differences between the noise and music?
Answer:

Noise	Music
1) The sounds which are not pleasant to hear are called noise. Eg: Dragging the almirah, machine, horn vehicles.	1) The sounds which are pleasant to hear are called music. Eg: Playing veena, playing sitar etc.
2) Noise is the irregular combination of sounds.	2) Music is the combination of sounds that are produced in an order.
3) Noise has no characteristics of sound.	3) Musical note has three important characteristics of sound.

Question 4.
Explain the sources which produce sound pollution in your surroundings.
Answer:
Sources of sound causing sound pollution:

1. Sounds of traffic and their horns.
2. Sounds in constructions of buildings at sites.
3. Sounds produced in industries.
4. Sounds in mines.
5. Sounds during explosions and bursting of crackers.
6. Sound pollution in our homes like mixer/grinders washing machines and electric motors.
7. Sounds due to printing machine.
8. Sounds due to soldering and welding, tinkering.
9. Sounds during the elections campaign.
10. Sounds due to mikes during festivals.

Question 5.
Write your suggestions about reducing sound pollution.
Answer:
We cannot stop sound pollution but we can reduce sound pollution with some measures.
Steps to be taken to reduce sound pollution.

1. Attach silencers to the bikes and other machines to reduce sounds.
2. Manufacture machines that work with lesser noise.
3. Use the TVs and tape recorders with low volumes in our home.
4. Plant trees to reduce sound pollution.
5. Avoid unnecessary usage of horns of vehicles.

Application of concepts

Question 1.
The sounds of crickets (insects) make us close our ears. Why?
Answer:
The sounds of crickets make us to close our ears because the frequency of their sound is high.
The frequency of the sounds of crickets is in ultrasonic range that is nearly 20,000 Hz. So we are unable to hear that sounds. So the sounds of crickets make us to close our ears.

Question 2.
Write the names of any three musical instruments that you know and explain how they produce sound.
Answer:

• Veena, Tabala, and Flute are the three musical instruments known to me.
• Veena produces sound by vibrating the stretched string.
• Tabala produces sound by vibrating the stretched membrane.
• A flute produces sound by vibrating the air column.

Question 3.
Draw the figures depicting low amplitude and high amplitude.
Answer:

Question 4.
“Vibrations in a body produce sounds”. How do you prove it?
Answer:
i. Put a hack-saw blade in between a table and a brick as shown in the figure and press it
and then leave abruptly. You listen to the sound and it is in vibrating mode.

ii. Ring your school bell and listen the sound carefully. Now hold the bell tightly with
your hands. You feel the vibration of bell when it is ringing. From the above experiments, you may notice that objects vibrate while they are producing the sound. Thus we can conclude that a vibrating body produces sound.

Question 5.
Write any two slogans to reduce sound pollution.
What we have learnt?
Answer:
“Avoid Sound Pollution – Save Bio-diversity”.
“Low Sound – Peaceful Mind’

Sound pollution affects the Bio-diversity. Vibrations of high frequency from cell phone tower cause the disappearing of sparrows. Crows and Eagles are also affected by the high frequency sound pollution. Hence Bio-diversity in nature collapsed.

Higher Order Thinking Questions

Question 1.
What is the effect of humidity on quality of sound propagation? is there any difference in propagation of sound in air during the summer and winter seasons? Discuss.
Answer:
Effect of humidity on quality of sound:

1. Quality or timber is the characteristics of a sound wave which enables us to know the person who is speaking without seeing him.
   Eg: If you hear news in Radio, we can recognise whether it is of male or female.
2. As the humidity in the atmosphere increases the quality of sound does not change.
3. If the humidity increases speed of the sound increases.
4. So in winter or on a cloudy day the speed of the sound increases and reaches the listener fastly.
5. Even in summer also the speed of the sound increases. But it does not increase so much like in winter, since (v ∝\( \sqrt{\mathrm{T}}\)) Velocity of sound increases with square root of absolute temperature.

Question 2.
How does sound pollution effect Biodiversity? Explain.
Answer:
Sound pollution (or environmental sound) is displeasing human, animal or machine-created sound that disrupts the activity or balance of human or human life.

Sound can have a detrimental effect on animals by causing stress, increasing risk of death by changing the delicate balance in predator/prey detection and avoidance, and by interfering with their use of sounds in communication especially in relation to reproduction and in navigation. Acoustic overexposure can lead to temporary or permanent loss of hearing.

An impact of noise on animal life is the reduction of usable habitat that noisy areas may cause, which in the case of endangered species may be part of the path to extinction. Sound pollution has caused the death of certain species of whales that beached themselves after being exposed to the loud sound of military sonar.

Multiple Choice Questions

Question 1.
An object which moves to and fro motion from rest known as ……………… .[ ]
a) Linear motion
b) vibration
c) simple motion
d) Angular motion
Answer:
b) vibration

Question 2.
The number of vibrations produced per second is known as ………………… .[ ]
a) Frequency
b) Shrillness
c) Vibration limit
d) Decibels
Answer:
a) Frequency

Question 3.
The audible sound range of man is …………………. . [ ]
a) 10-10000 Vibrations/sec
b) 20-20000 Vibrations/sec
c) 30-30000 Vibrations/sec
d) 40-40000 Vibrations/sec
Answer:
b) 20-20000 Vibrations/sec

Question 4.
The oval window has the surface area ……………… of the eardrum. [ ]
a) 1/10
b) 1/20
c) 1/30
d) 1/40
Answer:
b) 1/20

Question 5.
The shrillness of a sound is known as ……………….. . [ ]
a) Pitch
b) Vibration
c) Intensity
d) decibel
Answer:
a) Pitch

Suggested Experiments

Question 1.
Conduct an experiment to know the relationship between the intensity of sound produced by a body and its amplitude.
Answer:

Aim: To know the relation between the intensity of sound produced by a body and the vibrators of the body.
Apparatus: Wooden table, hack-saw blade or metal scale of 30 cm long, and a brick.

Procedure:

• Place the blade metal scale on the table with 10cm of the blade on the surface and rest of it in air.
• Keep a heavy brick on one end of the blade which is kept on the table.
• Vibrate the blade gently and observe the vibrations and simultaneously listen to the sounds.
• Repeat the same, 2 – 3 times and record the observations in the table.
• Now vibrate the blade using higher force. Observe the vibrations and listen to the sounds.
• Repeat this for 2-3 times and record the observations.

Force	Vibration of the blade scale	Intensity of sound
Small force
Large force

From the above activity, we conclude that as the force, increases the displacement as well as amplitude increases.

So when amplitude of sound increases, intensity of sound also increases.

Questions based on the above Lab Activity – 1

a. When do you hear a loud sound?
Answer:
When the scale is vibrating we can hear loud sound.

b. When do you hear a feebler sound?
Answer:
When the blade is vibrating we can hear feebler sound.

c. What difference do you notice in number of vibrations of blade/scale during loud and feeble sounds?
Answer:
Blade gives more vibrations while scale gives less vibrations in one second.

Question 2.
Conduct an experiment to identify Pitch or Shrillness of different sounds.
Answer:

Aim: Identifying pitch or shrillness of a sound. (or) Identify the relation between pitch and frequency.
Materials required: Wooden table, two hack-saw blades or metal scales of 30cm length and a brick.

Procedure:

• Place the first blade on the table with 10cm portion of the blade on the table and rest of it in air.
• Keep brick as weight on the 10cm portion of the blade which was kept on the table.
• Place the second blade on the table, with 25cm on the table and 5cm in air, Keep brick as weight on the scale. See the gap between two blades be 10 cm.

• Vibrate both the blades with same force. Observe the vibrations and listen to the sound produced.
• Repeat the same 2-3 limes and record observations in the table.

Blade length in air	Vibrations	Sound
Blade-1:25cm
Blade -2: 10cm

You mas notice that the number of vibrations produced by 25cm long blade is less than the number of vibrations produced by 10cm long blade.
The Sound produced by 10cm blade is more shrill than that of 25cm blade.
The shrillness of a sound is known as pitch.
The number of vibrations per second is called frequency.
The pitch of the sound depends upon its frequency.
In the above experiment more is the shrill, more is the pitch and it has more frequency.
Thus the sound produced a short blade (10cm) has high pitch and sound produced by (25cm) long blade has low pitch.

Questions based on the above Lab Activity

a. What difference do you notice in number of vibrations of two blades?
Answer:
We may notice that the number of vibrations produced are less in 25 cm long blade when compared to the vibrations of 10 cm long blade.

b. What difference do you notice in the quality of sound produced by them?
Answer:
The sound produced by 10 cm blade is more shrill when compared to that of 25 cm blade.

Suggested project works

Question 1.
Collect photographs showing various situations of sound pollution and prepare a report.
Answer:

1. Function where loudspeakers are used
2. Traffic ¡am and blowing horns
3. Sound pollution because of firecrackers

Question 2.
Collect the photographs of different musical instruments and paste in your scrapbook.
Answer:

Question 3.
Collect the photographs of local musicians and exhibit them in your class.
Answer:

Do you know?

Golconda Fort – Hyderabad
It is a famous fort in India. It is famous for many engineering and architectural marvels. If you clap your hands at a particular point under the dome it reverberates and can be heard at the highest point of the fort which is about 1 km away.

TS 8th Class Physics 5th Lesson Metals and Non-Metals Intext Questions

Think and Discuss

Question 1.
What is the effect of humidity on quality of sound propagation? Is there any difference in propagation of sound in air during the summer and winter sessions? Discuss with your friends. (Text. P. No. 74)
Answer:
Generally sound travels faster in denser mediums. Therefore as humidity increases, the speed of sound also increases. There is no change in its amplitude and frequency. But quality of sound changes.

Question 2.
“Vibrations produce sound and sound produces vibrations”. Is it true? Discuss. (Text. P. No. 75) (Information skills/Conceptual understanding/Making hypothesis)
Answer:
“Vibrations produce sound and sound produces vibrations. The above statement is true.
Vibrations produce sound. But we are able to hear a sound of range 20 Hertz to 20,000 Hertz frequency. If the frequency is less than 20 Hz or more than 20,000 Hz we are unable to hear, even though they produce sound.

“Sound produces vibration”. The sound is produced by vibrating body. But all the vibrations produced by sounds have not much amplitude. So we are not able to observe the vibrations even though those sounds produce vibrations.

Question 3.
“Our ear has the three media through which sound propagates.” Discuss with your friends as to whether the above statement is true. (Information skills/Making hpo1hesWConceptual understanding)
Answer:
Our ear has the three media (solids liquid and gaseous) through which sound propagates.
Pinna of external ear collects the vibrations. They enter into the ear canal. Through this canal, (gaseous (air) state) sound propagates and strikes the tympanum (eardrum) and make it to vibrate. Eardrum and other parts are considered as solid state.

The vibrations from the oval window transmits to the cochlea which is the inner part of the ear. The cochlea is filled with fluid, which transmits the vibrations. Here the fluid is considered as liquid state. So the statement, “Our ear has three media through which sound propagates”, is correct statement.

TS 8th Class Physics 5th Lesson Metals and Non-Metals Activities

Activity – 1: Listening to sound and predicting its source: (Text. P. No. 65)

Question 1.
Prepare list of sounds heard and the sources from which they might have originated. (Project/Field investigations)
Answer:
I sit quietly for a while and listen the sound from my surroundings.

Sound heard	Source of sound
1. Feeble barking	Dog from some distance
2. Bell ringing	Bell in school
3. Tick, Tick …….	From wall clock.
4. Tring, Tring …	Phone in my house.
5. Gala Gala	A few stones rattling in a metal box
6. Eela (whistling sound)	A student has produced the sound from her/his mouth

Activity -2:
Identifying different sounds: (Text. P. No. 65)

Question 2.
How does the student at blackboard guess the source of sound without actually seeing the source?
Answer:
Already student is familiar with these sounds and sound travelled through air and reached his ear.

Questions based on the above Activity – 2

a. How do objects produce sound?
Answer:
Objects produce sound due to vibrations.

b. Sound is a part of our daily life. Do you agree? Discuss. Flow? (Daily life applications/information skill/Making hypothesis)
Answer:

1. Throughout the day we are constantly exposed to different sounds.
2. Examples are people talking, birds chirping, cries of animals, sounds of autos, motorbikes, buses, lorries, tractors, trains etc.
3. Music played on loudspeakers at public places, televisions.
4. Sound is an unavoidable and integral part of our lives. We are always surrounded by sound.
5. Sound plays an important role in our lives. It helps us to communicate easily with each other.

c. What happens when objects made of metals are hit by a hammer or fall down from a height on a concrete floor?
Answer:
We will hear sound when objects made of metals are hit by a hammer or fall down from a height on a concrete floor.

d. How does a flute or a whistle produce sound?
Answer:
A flute or a whistle produces sound by making vibrations in air.

e. How would you feel if you touch a body while it is producing sound?
Answer:
feel their vibrations when I touch a body while it is producing sound.

Activity – 3:
VbratIne body produces sound: (Text. P. No. 66)

Question 3.
How do you prove that vibrating body produces sound?
(or)
Vibrating body produces sound. How do you prove this statement. (Project/Daily life applications! Experimentation)
Answer:

• Take a metal plate. Fill It with some water and let the water settle.
• Strike the brim of the plate with spoon. Observe the surface of water for waves on it.
• You listen to the sound. Touch the metal plate. You can feel the vibrations.
• From this we conclude that vibrating bodies produce sound.

Note: Students can write any activity given in page -67 in test book.

Questions based on the above Activity – 3

a. What have you observed while doing the above activities?
Answer:
When the object is vibrating then only we will be able to hear sound.

b. What changes took place in those objects?
Answer:
Objects will vibrate when they are producing sound.

c. How are they producing sound?
Answer:
The vibrating bodies produces sound

d. Is it possible to produces sound without vibration?
Answer:
No, it is not possible to produce sound without vibrations.

e. Does every vibrating body produce sound?
Answer:
No, every vibrating body does not produce sound.

f. Does sound has energy?
Answer:
Sound has energy.

Activity -4:
Sound has energy: (Text. P. No. 68)

Question 4.
How do you prove that sound has energy? (Experimentation & Field investigations)
Answer:

• Take a plastic bottle and a cell phone. Cut the top of the bottle so that it looks like a glass.
• Play songs on the mobile phone in high volume and place it in the bottle.
• Close the mouth of the bottle with a balloon using rubber band. So that it covets the boule as shown in the figure and stretch it tightly so as to behave like a diaphragm.
• Place some sugar crystals or some small sand particles and observe the movement of particles.
• Do the sanie activity after removing the phone from the bottle.
• When there is no cell phone inside the bottle, sand particles on diaphragm remain stationary.
• With the cell phone playing songs inside the bottle, the diaphragm vibrates which can be seen through dancing of sand particles.
• The sound produced by cell phone inside the bottle is responsible for these vibrations.
• Thus sound has energy to make sand particles vibrate on the diaphragm.

Activity -5 :
Producing a sound that resembles sound of rainfall: (Text. P. No. 69)

Question 5.
How do you produce a sound that resembles sound of rainfall? (Appreciation! Field investigation/Aesthetic sense and values)
(or)
How do you appreciate your friend to his magic to produce a sound that resembles sound of rainfall with fingers?
Answer:

1. My friend asked my classmates to start clapping with forefinger on left-hand palms.
2. Then add middle finger and clap again. Lastly, add ring finger and then small finger successively and reverse the process gradually.
3. All the students in our class did it simultaneously then the sounds produced resembled the rainfall.
4. All of our students appreciated my friend for this activity.

Activity -6 :
Observing the changes in sound: (Text. P. No. 69)

Question 6.
How do you prepare a ‘Jalatarang’ musical instrument? What do you observe from it? (Model Making/Experimentation/Making hypothesis)
Answer:

• Take 6 to 8 metal or glass bowls or tumblers.
• Fill them with water in increasing order.
• Strike gently each bowl or tumbler with a spoon.
• Each tumbler produces different types of sound.
• Now fill the bowls or tumblers with equal level of water.
• Strike each bowl like in above case and listen to the sound.
• Now every bowl produces same type of sound.
• From this we can conclude that sounds are produced by the vibrating bodies and the air passes through orfices of the instruments.

Questions based on the above Activity – 6

a. What difference do you notice in the sound produced?
Answer:
There is a variation in the sound produced by the two cases.

b. Why there is variation in the sound produced due to change in the water level of a bowl?
Answer:
Due to the change in the heights of air levels they produce different sounds.

Activity -7:
Observing the movements of vocal cords during the speech: (Text. P. No. 71)

Question 7.
Describe an activity to observe the movement of vocal cords during the speech.
Answer:

• Ask a friend to raise his neck up.
• Stretch a chocolate wrapper across his mouth and ask him/her to blow air on the wrapper forcibly.
• Observe the changes in movement at his/her throat.
• Ask him/her now blow again slowly and observe the difference in movements.
• During the first time the voice box gets tensed and produces high sound while the second time it is close to normal position of throat and produces lower sound.
• The sound produced in above activity is due to the combination of vibrations produced in wrapper and the vocal cord.

Questions based on the above Lab Activity

a. Does sound travel only in air?
Answer:
No, sound travels in air, solids, Liquids.

b. Does it travel in any other gaseous medium?
Answer:
Yes. sound travels in other gaseous medium.

c. Does sound also travel in other media like solids and liquids?
Answer:
Yes, sound travels in other mediums like solids and liquids.

Activity -8:
Observing sound oropa8ation solid (Text. P. No. 72)

Question 8.
Describe an activity to show that sound travels in solids.
Answer:

1. Take a metal or wooden strip. Strike it at one end and ask your friend to hear the sound by keeping his ears at the other end of the strip.
2. Your friend heard the sound at the other end of the strip.
3. Ask your friend to strike the table at one end and you listen to the sound produced Law keeping your ear on the other end of the table.
4. You heard the sound from the table.
5. From the above activities you can conclude that sound travels in solids like wood, metal etc.

Questions based on the above Activity-8

a. Are you able to hear the sound?
Answer:
Yes, we are able to listen the sound.

b. What is a median between you and your friend which is responsible for propagation of sound?
Answer:
The medium between me and my friend is solid.

c. Does sound travel in liquids?
Answer:
Yes, sound travels in liquids.

d. Can we hear the sound produced in water?
Answer:
Yes, we are able to listen the sound produced in water.

Activity – 9:
Propagation of sound through liquids (Text. P. No. 73)

Question 9.
How do you prove that sound travels through liquids? (Experimentation & Activity)
Answer:

• Take a bucket or a bathtub.
• Fill it with clean water.
• Take two stones and strike them against each other keeping your hands inside the water.
• Make sure that stones do not touch the body of the bucket.
• place your ear gently on the water surface.
• You hear the sound of striking stones.
• It indicates the propagation of sound through water.
• From the above activity, we conclude that sound travels through liquids.

Activity – 10:
Does the sound travel if there is no medium? (Text. P. No. 72)

Question 10.
How can you demonstrate that sound does not propagate through vacuum? (Experimentation/Daily life application/Field investigations)
Answer:

• Take a water tumbler or glass. Make sure that the tumbler or glass is dry.
• place cell phones small in size and play the ringtone of the mobile.
• Listen to the ringtone and its volume level.
• Cover the glass with a small plate and nd does no piopaate again listen to the ring tone and note the throush difference in volume of the sound.
• Now suck the air from the glass kping it dosel to your mouth.
• If you suck air quickly the rim of the glass stick around your mouth due to air lock.
• Listen to the volume of the ringtone at this stage.
• As you start sucking more and more air, the volume of the sound decreases gradually. If the air is sucked completely, you will not hear the sound at all.
• From this activity we conclude that sound does not propagate through vacuum and it requires a medium.

Questions based on the above Activity – 10

a. Why are some sounds loud?
Answer:
Because the number of vibrations in one second are flore so we can hear sounds loud.

b. Why are some sounds feeble?
Answer:
Because the number of vibrations in one second are less compared to other.

c. Is there any relation between the intensity of sound and vibrations of the body which produces sound?
Answer:
Yes, there is a relation between the intensity of sound and vibrations of the body which producing sound. If vibrations of body increase intensity of sound increases.

Lab Activity – 1

Question 1.
How do you explain the relation between the intensity of sound produced by a body and the vibrations (amplitude) of the body? (Making hypothesis/Experinwntation/Field investigation)
Answer:
Aim: To know the relation between the intensity of sound produced by a body and the vibrators of the body.
Apparatus: Wooden table, hack-saw blade or metal scale of 30 cm long, and a brick.

Procedure:

• Place the blade metal scale on the table with 10cm of the blade on the surface and rest of it in air.
• Keep a heavy brick on one end of the blade which is kept on the table.
• Vibrate the blade gently and observe the vibrations and simultaneously listen to the sounds.
• Repeat the same, 2 – 3 times and record the observations in the table.
• Now vibrate the blade using higher force. Observe the vibrations and listen to the sounds.
• Repeat this for 2-3 times and record the observations.

Force	Vibration of the blade scale	Intensity of sound
Small force
Large force

From the above activity we conclude that as the force, increases the displacement as well as amplitude increases.

So when amplitude of sound increases, intensity of sound also increases.

Questions based on the above Lab Activity – 1

a. When do you hear a loud sound?
Answer:
When the scale is vibrating we can hear loud sound.

b. When do you hear a feebler sound?
Answer:
When the blade is vibrating we can hear feebler sound.

c. What difference do you notice in number of vibrations of blade / scale during loud and feeble sounds?
Answer:
Blade gives more vibrations while scale gives less vibrations in one second.

Lab Activity -2

How do you identify the pitch or shrillness of a sound?
(or)
What is the relation between pitch and frequency? (Experimentation/ Making hypothesis)
Answer:
Aim: Identifying pitch or shrillness of a sound. (or) Identify the relation between pitch and frequency.
Materials required: Wooden table, two hack-saw blades or metal scales of 30cm length and a brick.

Procedure:

• Place the first blade on the table with 10cm portion of the blade on the table and rest of it in air.
• Keep brick as weight on the 10cm portion of the blade which was kept on the table.
• Place the second blade on the table, with 25cm on the table and 5cm in air, Keep brick as weight on the scale. See the gap between two blades be 10 cm.

• Vibrate both the blades with same force. Observe the vibrations and listen to the sound produced.
• Repeat the same 2-3 limes and record observations in the table.

Blade length in air	Vibrations	Sound
Blade-1:25cm
Blade -2: 10cm

You mas notice that the number of vibrations produced by 25cm long blade is less than the number of vibrations produced by 10cm long blade.
The Sound produced by 10cm blade is more shrill than that of 25cm blade.
The shrillness of a sound is known as pitch.
The number of vibrations per second is called frequency.
The pitch of the sound depends upon its frequency.
In the above experiment more is the shrill, more is the pitch and it has more frequency.
Thus the sound produced b)r a short blade (10cm) has high pitch and sound produced by (25cm) long blade has low pitch.

Questions based on the above Lab Activity

a. What difference do you notice in number of vibrations of two blades?
Answer:
We may notice that the number of vibrations produced are less in 25 cm long blade when compared to the vibrations of 10 cm long blade.

b. What difference do you notice in the quality of sound produced by them?
Answer:
The sound produced by 10 cm blade is more shrill when compared to that of 25 cm blade.

Telangana SCERT 8th Class English Guide Telangana State Unit 1A The Tattered Blanket Textbook Questions and Answers.

TS 8th Class English Guide Unit 1A The Tattered Blanket

PRE-READING (Motivation/Picture Interaction):

Look at the pictures and answer the questions that follow.

Question 1.
What do you observe in the pictures ?
Answer:
These two pictures are family photographs. The first photograph with limited members reflects a nuclear family. In this photograph we can see a husband and a wife with their two children. The second photograph with many members reflects a joint family. In this photograph we can see the people of three generations. There are grandmother and father, sons and daughters and grandchildren.

Question 2.
What type of families do we find in our present society ? Why ?
Answer:
We find nuclear families in our present society nowadays. Formation of nuclear families started during the last four decades. Many changes took place in family culture and society. The needs of family were increased to a large extent in financial matters. Modernisation and industrialisation took place. People feel that smaller family units could move more easily to find economic opportunities in other areas. People who are educated in a family should move from their home towns in search of jobs.

Question 3.
Which family do you like ? Why ?
Answer:
I like joint family. The joint families are happy ones. The elders in the joint family with their vast experience give good pieces of advice to the younger ones and put them in right direction. The younger ones learn co-operation, sacrifice, selfless service, obedience, sympathy and broad-minded nature, etc. The child, the employed, the sick, the aged and physically disabled people are well taken care of. There would be more affection and love among the members of the joint family.
(OR)
I like small family. Small families help every country in controlling the growth of population. A small family promises well-fed and healthy family members. Parents in a small family can pay due attention to the upbringing and needs of their children. The children are exposed to more educational, intellectual and cultural opportunities. Hence, I can say that a small family is a happy family.

ORAL DISCOURSE

Question.
Debate : “Small families are happy families.”
Answer:
Child 1 : I personally feel that small families are happy families. The living cost of larger family is much higher as it needs to expend more on food, cloths, education and other things when we compare with the expenses of a small family. A small family promises well-fed and healthy family members. In a small family, kids receive more love and attention from the parents.

Child 2 : In my opinion, large families which have more members are happy families. In large families children get a chance to receive more feedback from peers about the way they act and they have more opportunities to interact with peers. In a small family, it is hard to find someone that one can get along with, so one feels lonely.

Child 1 : My knowledgeable opponent is of the opinion that large families are happy families. I am sorry to differ with him/her. Children from small families fare better than children from large families. In small families, parents have more time to devote to the caring of children. Parents look after them well.

Child 2 : I disagree with my opponent’s opinion. In big families, children learn empathy, teamplaying, time management and how to avoid disputes.

Child 1 : It’s my feeling that parents in a small family can fulfil the needs of one or two kids. They can pay due attention to their upbringing and needs. In a big family, parents can’t give their best support to everyone but in a small family, parents have few children to look after so they can give more support to them.

Child 2 : That’s purely your idea but the reality is different. I think that it is a blessing to have a big family. If we have aunts, uncles and others along with us we learn more from them. With their vast experience, they give good pieces of advice to the younger ones and put them in the right direction.

Child 1 : I don’t agree with my worthy opponent. Small families help every country in controlling the growth of population. The growth in population effects the quality of life.

Child 2 : I feel that everyone would take care of everyone else in a big family. The child finds a lovely time playing with his/her peers. The old people have the company of younger ones.

Child 1 : In my opinion, small families provide a good environment for children to grow up. In a small family, children are exposed to more educational, intellectual and cultural opportunities. In a large family there is a lack of privacy but it is not the case with a small family. Hence I opine that small families are happy families.

Child 2 : I feel that parents in a large family divide the chores and responsibilities among the children so they can do work faster. The holidays can be more festive with all the members of the family. They celebrate together each and every important occasion. Therefore I conclude that large/big families are happy ones. I prefer to be a member of a big family.

Answer the following questions.

Question 1.
Why didn’t the mother recognise Gopi ? How did he feel?
Answer:
The mother did not recognise Gopi because she lost her power of memory. He was not much worried. He took it in an easy manner.

Question 2.
Why do you think Gopi didn’t get anything for his mother?
Answer:
Gopi has no love for his mother. It is proved when he came back home after five years. That too, to ask his sister to sell his share of property for getting money.

Question 3.
The mother could not remember Gopi. Do you think Gopi remembered his mother? What does it suggest?
Answer:
Gopi did not remember his mother. He came to see her after five years. That too, with the intention of asking his sister to sell his share of property for getting money. It suggests that he has no love for his mother.

Question 4.
What is meant by the expression the ‘tattered blanket’?
Answer:
In the light of the lesson the ‘tattered blanket’ means a ‘wounded soul’.

Question 5.
Why didn’t Gopi answer his sister’s question, ‘Do you remember your Amma?’
Answer:
Gopi did not answer his sister’s question whether he remembered his Amma because he ”eally did not remember his mother.

Question 6.
If you were Gopi’s sister, how would you respond to his behaviour?
Answer:
If I were Gopi’s sister, I would be angry with him. I would not allow him to sell his share of property.

Vocabulary:

I. Fill in the blanks with the most appropriate words from the box. Remember, the box has some extra words.

Question 1.
All my attempts to make him happy proved ________.
Answer:
futile

Question 2.
It was very cold. So, ________ in a corner.
Answer:
huddled

Question 3.
Forced by her parents, Sita ________ took the diploma course.
Answer:
exasperatedly

Question 4.
What are you ________? I can’t hear you.
Answer:
mumbling

Question 5.
The news that he was denied promotion caused ________ to him.
Answer:
irritation

II. Tick (✓) the words that are similar in meaning to the underlined words.

Question 1.
His mother made a futile attempt to get up.
a. barren
b. limited
c. useless
d. empty
Answer:
c. useless

Question 2.
It’s all tattered now.
a. spoiled
b. old
c. dirty
d. tom
Answer:
d. tom

Question 3.
There is a cold mist in the mornings.
a. ice
b. snow
c. fog
d. win
Answer:
c. fog

Question 4.
It’s iust like a bali of knotted yarn.
a. very small
b. rounded tightly
c. joined
d. tied
Answer:
b. rounded tightly

Question 5.
I can’t make both ends meet with my salary.
a. earn a lot of money
b. spend a lot of money
c. earn just enough money
d. give all that one has
Answer:
c. earn just enough money

Grammar:

Phrases and Noun Phrases:

I. Look at the following sentences from the text and observe the underlined part in each sentence.

She saw a bald, fat, middle-aged man.
Discussion :
• Which word in the underlined part is important?
• The underlined part in the above sentence has more than one word. It is called a phrase.
• The underlined part ‘a bald, fat middle-aged man’ functions as a Noun Phrase.
• Here the word ‘man’ is important and all other words add more information to that word. So it is called a Noun Phrase.

Detailed Information on Noun Phrases:

A noun phrase includes a noun—a person, place, or thing—and the modifiers which distinguish it.

You can find the noun dog in a sentence, for example, but you don’t know which canine the writer means until you consider the entire noun phrase: that dog, uncle Raju’s dog, the dog on the sofa, the neighbor’s dog that chases our cat, the dog digging in the new flower bed.

Modifiers can come before or after the noun. The ones that come before might include articles, possessive nouns, possessive pronouns, adjectives, and/or participles.
Articles: a dog, the dog

Possessive nouns:
uncle Raju’s dog,
the neighbor’s dog,
the police officer’s dog

Possessive pronouns: our dog, her dog, their dog
Adjectives: that dog, the big dog, the spotted dog
Participles: the drooling dog, the barking dog, the well trained dog

Modifiers that come after the noun might include prepositional phrases, adjective clauses, participle phrases, and/or infinitives.

Prepositional phrases: a dog on the loose, the dog in the front seat, the dog behind the fence
Adjective clauses: the dog that chases cats, the dog that looks lost, the dog that won the championship
Participle phrases: the dog whining for a treat, the dog clipped at the groom¬ing salon, the dog walked daily
Infinitives: the dog to catch, the dog to train, the dog to adopt

Less frequently, a noun phrase will have a pronoun as its base—a word like we, everybody, etc.—and the modifiers which distinguish it. Read these examples: We who were green with envy
We = subject pronoun; who were green with envy = modifier.
Someone intelligent
Someone = indefinite pronoun; intelligent — modifier.
No one important
No one = indefinite pronoun; important – modifier.

Textual Exercise – 1

Identify some more noun phrases from the story and write them below.
Answer:
a. a futile attempt
b. a thin bath towel
c. her wrinkled cheeks
d. my salary
e. a long time
f. a red blanket
g. a great help

Textual Exercise – 2

Complete the sentences with noun phrases using the words given in brackets.

Question 1.
I bought ________, (beautiful/a/umbrella/red).
Answer:
I bought a beautiful red umbrella.

Question 2.
We saw ________ in the zoo. (baby/a/elephants/of/couple).
Answer:
We saw a couple of baby elephants in the zoo.

Question 3.
Our grandfather lives in ________ (big/house/a/stone-built).
Answer:
Our grandfather lives in a big stone-built house.

Question 4.
Ramya has ________ (nice/a/sari/silk).
Answer:
Ramya has a nice silk sari.

Writing:

I. Read the following paragraph, taken from the story.

Delhi is too expensive. You know I have four children to look after now. I can’t make both ends meet with my salary. And one has to keep up one’s status. It will be a great help if I can raise some money by selling my share of the family property. I came to talk it over with you.

Now, write a short essay on how to keep up family ties despite economic pressures (You may use the hints given below).

• Impact of economic pressures
• Lack of time to spend with the family
• Lack of love and affection
• Absence of human relationships

Answer:
What makes us happy? Is it money, job, house, clothes, rich food, luxury or something else? Yes, it is something else. It is healthy relationship among family members – dad, mom, children, husband, wife etc. We deeply desire to live happily. The impact of economic pressures, lack of time to spend with the family, lack of love and affection among the members of the family and absence of human relationships have played a vital role in destroying the family ties in recent times. To avoid this and keep the family ties in a good condition we have to take care.

We, Indians give strong values to family relationships. It is our culture that has been followed from olden days. In earlier days and in some parts of India, still there are joint families. Joint families comprise many people – father, mother, children, grandparents, grandchildren etc. In these families, there will be a strict hierarchy. The elder person in the family will be the head of the family. Ladies do household duties, look after their children, take care of their husband and parents etc. There will be a number of children in a joint family. They will learn to share what they have with others, to love and respect elders, to adjust themselves to the society or others from their younger age.

But nowadays the number of joint families is getting low (decreasing). Parents are working. Children are studying apart from their parents. They can’t always stay together with their grandparents. Thus the concept of nuclear families has emerged. In nuclear families, there will be father, mother and at most two children. The parents take -care of their children. Also the income of parents is more compared to those in olden days.

Traditions give us a feeling of security — an important thing for adults and children. They help us feel that the world is a good place and life is worth living. They can be especially important when there are transitions in family life. Economic pressures are common in everybody’s life. So don’t allow them dominate your family relationships. People are busy nowadays.

They usually don’t find time to spend with the members of their family. But we should spend our leisure time and holidays for our children and other members of the family. The first road block in the path of healthy relationship is non communication or critical communication. So we should have effective and positive communication with our family on regular basis.

Let the television be silent. Let us listen to our brothers, sisters, children, husband, wife, grandfather and grandchildren. We should show our love and affection in time of need. In a family it is important to show affection to each other. A family can grow closer as they receive love and support from each other. When we are interested in others and kind to them, we begin to understand and appreciate them more. We also begin to understand how much our kindness means to others. When family members show kindness to each other, families work together better. One thing that can help is being able to understand how others feel. Understanding how others feel is called empathy.

Listening:

I. Listen to your teacher making an announcement and answer the following questions.

An Announcement on the Radio

Prashanth, a thirteen year old boy has been missing since last Sunday. The boy is in blue trousers and pink T-shirt. He can speak Telugu, Hindi and English. He has fair complexion. He is fond of movies. His parents are much worried about him. Whoever finds Prashanth will be rewarded. You may contact the Sub-Inspector of Police, Vidya Nagar, Thiruvananthapuram. (Mobile No. 99XXXXXX00)

Answer the following questions.

Question 1.
What is the announcement about?
Answer:
The announcement is about the missing of a thirteen-year-old boy, Prashanth.

Question 2.
What are the features of Prashanth?
Answer:
Prashanth is in blue trousers and pink T-shirt. He has fair complexion.

Question 3.
Where do you generally listen to such announcements?
Answer:
We generally listen to such announcements in crowded places like bus stops, markets etc.

Question 4.
Think of some announcement you may make or listen at school.
Answer:
A boy from the dais of a school assembly says ‘My school bag is missing. It is red. It consists of 6 textbooks, 10 notebooks, a compass box and my lunch box. Whoever finds my bag will be rewarded with a 5 star chocolate. You may contact me at Class – VIII, Section – ‘A’. My name is Vinay Kumar.

Question 5.
What are the other ways to trace the missing persons or things?
Answer:
Sticking posters on walls, giving announcements in newspapers, announcing on TV, publishing pamphlets etc., are the other ways to trace the missing persons or things.

Study Skills:

Family related information.

Is yours a nuclear or joint family ?
Now write a paragraph describing the types of families using the information given in the above tree diagram.
Write which type of family you prefer and why.
Answer:
Types of Families:

Nuclear Family:

A nuclear family is a family group consisting of father and mother and their children, who share living quarters. This can be contrasted with an extended family.

Nuclear family grows out of joint/extended family when there is migration from village to city for employment or other reasons where joint family is not possible due to paucity of needed larger residential accommodation, different occupation etc. That is why it is mainly seen in urban areas, cities and metropolis.

Nuclear families may also exist in rural areas because the joint family cannot go on indefinitely owing to physical and social limitations. There is a limit to the number of people a house can accommodate and thus, there is bound to be fission into smaller nuclear families in the family cycle of development.

Merits of a Nuclear Family :
Unlike the joint family, there is greater degree of freedom for spouses in the nuclear family. The status of the woman is higher and she often takes up employment outside the home. The material well-being of children, such as healthcare and education, is higher because of more resources available. Nuclear families are adaptable to social change.

Drawbacks :
The nuclear family misses all the advantages of joint living. It is too isolated and uncon-nected to elicit support or assistance during need or crisis. Its limited size poses practical problems for child rearing and care, more so when the mother works outside.

Children are deprived of a wider social world, emotional bonding, love and affection that a joint family provides. The old parents are left in the village or at old age homes without personal care.

Joint Family :

Joint Family is an extended family arrangement prevalent among the Hindus of the Indian subcontinent, consisting of many generations living under the same roof.

All the male members are blood relatives and all the women are either mothers, wives, unmarried daughters, or widowed relatives, all bound by the common relationship. The joint family status being the result of birth, possession of joint cord that knits the members of the family together is not property but the relationship.

Six key aspects of Joint Family are :

• head of the family takes all decisions
• all members live under one roof
• share the same kitchen
• three generations living together (though often two or more brothers live together, or father and son live together or all the descendants of male live together)
• income and expenditure in a common pool, property held together.
• a common place of worship
• all decisions are made by the male head of the family.

Merits of a Joint Family :

The joint family is ideally suited for land-based rural families for its economic, social and psychological advantages. The joint operation of property allows increased efficiency of pooled labour and economies of a single kitchen and household. It provides for efficient geriatric and childcare, as there are many women to look after them.

This enables mothers to work in fields or do household work. Children grow up with care, love and affection from grandparents, uncles, aunts, cousins etc., besides their own parents. Joint family is an ideal setting to learn virtues of co-operation and collective living for the young people.

Family festivals and occasions can be celebrated more elegantly, enhancing the prestige of all the members. In general, joint family ensures the happiness and well-being of all its members.

Joint families may also own industries/business (besides agriculture). There are many well known industry/business houses running their enterprises jointly owned them by brothers etc., in a joint family.

Drawbacks :
The system is not without disadvantages though. Women in general have a low status and are often excluded from decision-making. There is little freedom for junior male members. The family, more based on tradition, may not be open to change or accepting new elements. The weight of the family is heavy on young couples. It hinders the process of individual freedom.

When compared with nuclear family system, joint family system has many merits and advantages. So I strongly prefer joint family system.

The Tattered Blanket Summary in English

Kamala Das’s ‘The Tattered Blanket’ exposes the bitter truths of life in a stunningly simple manner. After five years Gopi comes to Kerala to see his mother. Gopi is a big officer in Delhi living with his wife Vimala and his children. He has come to Thiruvananthapuram as a part of his official assignment. He just dropped in on his way back to meet his mother. His mother is very old. She lives with his eldest sister Kamala who is a widow. When he arrived unexpectedly at his home in the countryside, his mother was lying in an armchair on the veranda.

The mother fails to recognise her son Gopi. She believes that Gopi is still a school boy. She doesn’t recognise anybody. Sometimes her memory is quite sharp, sometimes she forgets the present, but remembers the past. When her memory is very sharp, she asks about Gopi’s letters from Delhi. Kamala tells her a lie that everything is fine with Gopi, his wife and kids. But Gopi doesn’t write any letters to his mother.

The mother doesn’t recognise her son. She asks her son Gopi ‘Who is your Amma? What is her name? Where does she live Is it far from here?’ But the mother has the picture of her son in her mind. She says, ‘My son is in Delhi a Government Officer. He has Kesariyogam (well settled). He draws a salary of two thousand five hundred rupees.’

The mother tells Gopi if he meets her son, ask him to send her a blanket. A red one. She has a blanket, the one Gopi bought for her when he was studying in Madras. It is all tattered now, just a ball of knotted yarn. Gopi has come home to ask his sister to sell his share of land and get some money for him. Kamala knows that Gopi has come only for money, not to see their mother. It took more than five years for hir, to find time to come home.

Kamala says, ‘Amma is eighty three now. I don’t think she will pull on much longer. It took you so long to visit her after the last time.’ But Gopi has his excuses for not visiting Amma. He says ‘But Amma can’t remember who I am.’

The story ends with Kamala’s question to Gopi, ‘But do you remember your Amma?’ Amma doesn’t recognise her son because she has lost her power of memory. In fact forgetfulness is a blessing for her. Her son doesn’t have any love for his mother.

This is one of the brilliant short stories penned by Madhavikutty in Malayalam. Her focus has always been on the tormented female self, craving for love. She is concerned with the condition of women and the way in which they were betrayed by society. In ‘The Tattered Blanket’ the mother craves for her son’s love. Her son is evergreen in her memory. But she has been overpowered by forgetfulness. She needs a red blanket because the old one is tattered. Here the blanket represents the warmth of her son’s love. She actually needs her son’s love. The tattered blanket symbolises the tattered soul of the mother.

In ‘The Tattered Blanket’ Kamala Das (Madhavi Kutty) portrays the poignant voice of wounded womanhood.

About the Author:

Kamala Das (1932-2009) is the daughter of the famous Malayalam poet- Balamani Amma and V.M. Nair. She is an internationally known poet, short story writer and novelist who writes effortlessly both in English and Malayalam. She has received many awards for her literary work. Some of them are Asian Poetry Prize, Kent Award for English Writing from Asian Countries, Asian World Prize, Sahitya Academy Award and Vayalar Rama Varma Sahitya Award.

Glossary:

thinna (n) : sit out (elevated place on the veranda)
futile (adj) : unsuccessful
huddled (v) : held arms and legs close because of fear or cold
thinna (n) : platform
reluctantly (adv) : not willing to do something
screwing up eyes : narrowing the eyes to look more carefully
dropped (v) : came/visited
note of alarm : fear or worry
awkwardly (adv) : uncomfortably
wrinkled (adj) : having folds in skin on face
quite (adj) : reasonably ; to some degree ; to some extent
on toes (idm) : busy, ready to work
mumbling (v) : speaking unclearly and quietly
exasperatedly (adv) : very annoyed
Kesarlyogam (n) : well settled (in Malayalam)
tattered (adj) : torn
knotted (adj) : twisted into a ball
irritation (n) : annoyance/impatience/anger

TS Board Telangana SCERT Class 8 Physics Solutions 3rd Lesson Matter Around Us Textbook Questions and Answers.

TS 8th Class Physics 3rd Lesson Questions and Answers – Matter Around Us

Reflections on concepts

Question 1.
Why do some fibres are called Synthetic? Explain.
Answer:

• Synthetic fibres are not obtained from plant or animal source hut are made by human beings using raw materials obtained from petroleum-based chemicals.
• Petrochemicals are subjected to various chemical processes to obtain synthetic fibres.
• That is the reason why they are called synthetic fibres or simply artificial fibres.

Question 2.
What are thermosetting plastics. Give two examples.
Answer:
The plastics which moulded once can’t be softened by heating are known as thermosetting plastics.
Bakelite and melamine are examples for thermosetting plastics.

Question 3.
Give reasons “for using plastic containers as storing devices.” (AS )
Answer:

• Plastic material will not corrode easily.
• Plastics are non-reactive with other materials or chemicals.
• Plastic is very light, strong, durable and can be moulded into different shapes and sizes.
• Plastics are generally cheaper than metals. Because of the above reasons plastic containers are used as storage devices.

Question 4.
List out the objects made up of Acrylic.
Answer:
The following objects are made up of Acrylic

• Knitted apparels such as fleece, socks, sportswear, and sweaters.
• It is also used in Craft Yarns, upholstery fabrics, carpets, luggage swings and vehicle covers.
• Petrochemicals are subjected to various chemical processes to obtain synthetic fibres.
• That is the reason why they are called synthetic fibres or simply artificial fibres.

Question 5.
Draw and explain the diagram of Universal recycling symbol.
Answer:
To identify the plastic we look at the recycling icon, the chasing arrows. Inside the arrows, there will he a number that identifies the polymer. When the number is omitted, the symbol is known as the ‘Universal Recycling symbol’, indicating generic recyclable materials.

Application of concepts

Question 1.
How synthetic fibres have changed our daily life?
Answer:
Synthetic fibres changed our daily life, dressing style.

1. Production and maintenance of natural fibres are very difficult and time taking. But synthetic fibres are cheaper. They can be dyed in a wide variety of colours.
2. We are able to mix the synthetic fibres with other fibres (blending) for better clothing.
3. Synthetic fibres absorb less water and dry at a faster rate. Some are even waterproof.
4. They are durable, less expensive, readily available, affordable and are easy to maintain.
5. They are strong and light in weight.
6. Synthetic fibres are not only used for clothing but also for various purposes.
7. Today’s life without synthetic fibre cannot be imagined.
8. We need to use synthetic fibres in such a manner that we can enjoy their good qualities and at the same time minimise environmental hazards for the living communities.

Question 2.
What would happen, if we make electric switches with thermoplastics.
Answer:
Electric switches are generally made by thermosetting plastic, which will not change its shape on heating and has a stable structure. If electric switches are made by thermoplastics, they will be softened to the heat produced during the passage of current. It is very dangerous to the people. It causes electric shock or short circuit.

Question 3.
What could be the consequences if plastics are not properly disposed?
Answer:

1. Plastics take several years to decompose compared to other materials.
2. Slow decomposition of plastics causes environmental pollution.
3. The burning processes of synthetic material is also very slow and more over they can’t be burnt completely with ease.
4. The process of burning releases a lot of poisonous fumes into air causing air pollution.
5. So avoid or minimize the use of plastic.
6. “Plastic bags are more dangerous than atom bomb for future generations’.

Question 4.
Rani wants to buy clothes to her parents for winter wear.What types of clothes would you suggest? Specify reasons.
Answer:
I suggest Rani to buy clothes which give warmth to our body. Sweaters, shawls and blankets give warmth to our body. These are made up of natural wool or acrylic, a synthetic fibre. Generally wool is very costly and number of sheep would be needed to obtain wool for sweaters. So I suggest to buy sweaters and shawls made up of acrylic, which is relatively cheap.

Question 4.
Is there any such effort for solid waste management taking place in your Village/Town ? How do you appreciate 4R principle?
Answer:
Yes, In our town solid waste management taking place. The solid wastes are converted into electricity, in our town. Some of the solids wastes are converted into compost.

I appreciate 4R principle. It is for creating an eco-friendly environment, by reducing the use of plastics, reuse of unused plastic items, recycling new articles from the old plastics and recovering the resources like electricity, heat and compost from solid wastes. In these was 4R principle is eco-friendly, Hence I appreciate this 4R principle.

Question 5.
Where do we use the process of recycling? How is it useful? Give examples.
Answer:

1. Generally, we might have noticed our mother selling old plastic articles which are broken and not useful to the local vendor.
2. They collect all plastics from the households and send it for recycling.
3. From this recycled plastic new products are prepared after giving it a proper treatment.
4. Recycling can be used to obtain materials from which the original products were made.

Higher Order Thinking Questions

Question 1.
What made the human beings to search for the alternative for natural fibres?
Answer:
Natural fibres like cotton, wool and silk are very costly. it is not even accessible to all. Production and maintenance of natural clothes are also very difficult and time taking jobs. On the other hand synthetic fibre is cheap, absorbs less water and dry at a faster rate. Some are even waterproof. They are durable, less expensive, readily available, affordable and are easy to maintain.

Question 2.
Imagine what would happen if we do not discover plastics?
Answer:

• If we do not discover plastics, we depends on metals for many purposes in our daily life.
• If we use iron pipes they will rusted and they are not easily mouldable like plastic pipes.
• Metals will not be converted into any shape as plastics.
• We may be got electric shock if we are not discovered plastics which are used as covering for electric wires in houses.
• Plastics have also replaced glass items.
• Nowadays it is impossible to imagine our life without plastics.

Question 3.
indiscriminate usage of plastic is a serious threat to biodiversity. What are the efforts of Government and Non-government organizations in this regard?
Answer:
Indiscriminate usage of plastic is a serious threat to biodiversity. We need to use synthetic fibres and plastics in such a manner that we can enjoy their good qualities and at the same time minimize the environmental hazards for the living communities.

The government banned the usage of low-density carry bags which are not recyclable. We have to follow the ways and means of ‘solid waste management order given by supreme court.

N.G.Os, Government and the people follow the 4R principle. The solid waste should be converted into resources such as electricity, heat, compost and fuel through thermal and biological means.

Question 4.
Thermoplastics are eco-friendly than thermosetting plastics? Do you agree with statement?
Answer:

1. Thermoplastics are more eco-friendly than thermosetting plastics because these plastics are easily recyclable.
2. These are softened and remoulded on heating.
3. Thermosetting plastics become hard and can not be remoulded on heating. They are not recycled. Hence thermoplastics are more eco-friendly than thermosetting plastics.

Question 5.
The introduction of synthetic fibres in the textile industry brought revolutionary change across the world in the dressing patterns irrespective of culture and customs. How do you appreciate this?
Answer:
I appreciate the introduction of synthetic fibres because they possess unique characteristics which make them popular dress materials. They dry up soon, are durable, less expensive, readily available and easy to maintain. Thus the introduction of synthetic fibres in the textiles industry brought revolutionary change across the world in the dressing patterns irrespective of culture and customs.

Multiple Choice Questions

Question 1.
Rayon is prepared by [ ]
a) Coal
b) Oxygen
c) Fibre
d) Cellulose
Answer:
d) Cellulose

Question 2.
Necessity of labels on clothes [ ]
a) Required by law
b) To identify fabric content
c) Both A and B
d) They do not decompose
Answer:
b) To identify fabric content

Question 3.
The material which is not decomposed by natural process is called [ ]
a) Non bio-degradable material
b) Bio-degradable material
c) Polyester
d) Nylon
Answer:
a) Non bio-degradable material

Question 4.
The symbol represents [ ]
a) PET
b) HDPE
c) LDPE
d) Others
Answer:
b) HDPE

Question 5.
Which is a Natural fibre among the following? [ ]
a) Rayon
b) Nylon
c) Polyster
d) Silk
Answer:
d) Silk

Suggested Experiments

Question 1.
Conduct a flame test to identify Thermoplastics and Thermosetting plastics.
Answer:
Aim: Identifying thermoplastic and thermosetting plastics by flame test.
Materials required: Tong, spirit lamp, samples of plastics (Collect small pieces of plastics from the objects like comb, toothbrush handle, plastic bucket, handle of utensil, and electric switch, piece of melamine of meals plate and coffee mug)

Procedure:

1. Take a spirit lamp and light it.
2. Clamp one piece of plastic sample say piece of toothbrush with tong.
3. Place the sample on spirit lamp flame.
4. Observe the changes during the burning of sample.
5. Note your observations like whether sample are being softened or burnt with smell or become hard etc.
6. Repeat procedure with other samples.
7. Record your observations sample-wise in the following table.

Question 2.
Take a wool, silk, cotton thread, bandage, piece of umbrella cloth, thread of sweater, piece of rope and carefully conduct a flame test. Based on smell and type of melting Classify them as natural and artificial fibres.
Answer:

Type of Thread Fibre	Flame Test result	Natural/ Artificial Fibre
1. Wool	Smells like burning hair	Natural fibre
2. Silk	Smells like burning hair	Natural
3. Cotton thread	Smells like burning paper	Natural
4. Bandage	Smells like burning paper	Natural
5. Piece of plastic	Melts in the flame	Artificial
6. Thread of sweater	Melts in the flame	Artificial
7. Piece of rope	Smells like burning hair.	Natural

Question 3.
Collect small pieces of plastic from some objects and conduct a flame test. Record the observations and classify them into Thermoplastic/Thermosetting plastics.
Answer:

Name of the plastic sample	Softened/become hard on heating	Thermoplastic/ Thermosetting plastic
1. Toothbrush handle	Softened	Thermoplastic
2. Comb	Softened	Thermoplastic
3. Piece of bucket	Softened	Thermoplastic
4. Handle of utensil	become hard	Thermosetting plastic
5. Electric switch	become hard	Thermosetting plastic
6. Meals plate	become hard	Thermosetting plastic
7. Coffee mug	become hard	Thermosetting plastic

Suggested Projects

Question 1.
Prepare a table of various synthetic fibres which are used to make household articles from them.
Answer:

Type of Synthetic Fibre	Source Material	Articles made from it
1. Nylon	Coal, water and air	Ropes, tents, sarees, toothbrush, bristles fishing nets, etc.
2. Rayon	Wood pulp, some chemicals	Clothes, bed sheets, carpets, sanitary products, diapers and bandages.
3. Acrylic	Coal, air, water, oil and limestone	Fleece, socks, sportswear, sweaters, carpets, vehicle covers
4. Polyester	Chemicals mainly dicarboxylic acid and dihydric alcohol	Bottles, utensils, films, wires

 

Question 2.
Collect the figures made up of thermosetting, thermoplastics used in your daily life and make a poster.
Answer:
Articles made up of thermoplastics:

Articles made up of thermosetting plastics:

Question 3.
Prepare a chart which can explain recycling codes, full names and acronyms of plastic and its usage for various household articles, recycled or not, if recycled what will be made from that.
Answer:

TS 8th Class Physics 3rd Lesson Matter Around Us Intext Questions

Think & Discuss

Question 1.
Which fibre source material Is not exhaustible? Why? (Text. P. No. 33) (Making hypothesis)
Answer:
Synthetic fibres sources are not exhaustible. Because synthetic fibres are man-made. They are prepared from petroleum-based substances or petrochemicals. The sources of synthetic fibres are cheap and made from different man-made processes. So they are not exhaustible.

Question 2.
How synthetic fibres evolved to the present position? (Text. P. No. 34 (Daily life application/Appreciation)
Answer:
Synthetic fibres dry up quickly. They are durable; less expensive. They are readily available and easy to maintain. Some cotton fabrics Like rayon, absorb moisture or sweat, hence keep light weight.

Most of them are elastic, due to which they retain their original shape when compressed or stretched. They do not wrinkle easily, retain their original shape. They can handle heavy loads without breaking.

Question 3.
If we use cotton cloth and cotton ropes in preparing a parachute what will happen? (Text. P. No. 36) (Making hypothesis/Daily life application)
Answer:
Nylon is much stronger than other threads, nylon thread is stronger than steel wire of same thickness. So we use nylon fibre to prepare parachutes. If you use cotton ropes in preparing a parachute the rope may be cut easily because it is not as strong as nylon. Cotton also absorbs water easily. Absorbing water makes cotton weak and cause the fibre to break.

Question 4.
Traditionally fishermen used cotton nets. Now they are using nylon nets. What could be the advantage of nylon nets? (Text. P. No. 36) (Application in daily life/Rio diversity)
Answer:
Cotton absorbs water easily. Absorbing water makes cotton weak and causes the net to break. And it increases the weight o the net. Nylon fibre is strong, elastic and light in weight. It does not absorb water and easy to wash, So fishermen are using nylon nets.

Question 5.
Nylon sarees are much better than the cotton sarees. Is it better to use only nylon sarees? Do you agree with this? (Text. P. No. 36) (Application to daily life/Appreciation)
Answer:
Nylon sarees are much better than the cotton sarees. I also agree with that. Because nylon Is cheaper, light weight does not absorb water and easy to wash.

Question 6.
What characteristics make artificial rayon better than natural silk? (Text. P. No. 37) (Conceptual Understanding/Making hypothesis/Aesthetic sense)
Answer:
Rayon is not perfect, because it is made from plant cellulose. It absorbs water easily. Absorbing water makes rayon weak and causes the fibre to break.

Question 7.
If you want to purchase a doormat made of synthetic fibre. Which synthetic fibre door mat will you select? Why? (Text. P. No. 37) (Applications in daily life)
Answer:
If I want to purchase a door mat made of synthetic fibre, 1 select door mat made of rayon mixed with wool. Because it is cheaper and also be dyed in wide variety of colours. It also absorbs water, as natural wool and cotton.

Question 8.
If sanitary diapers and bandages are made of nylon, what happens? (Text. P. No. .37) (Making hypothesis/Field investigation/Conceptual understanding)
Answer:
Generally, sanitary diapers and bandages are made by rayon because it absorbs water and wet. If sanitary diapers and bandages are made by nylon, nylon does not absorb water and wet. So the purpose of diapers and bandages are not fulfilled.

Question 9.
Which type of blended fabrics do you find more comfortable in winter? Why? (Text. P. No. 38) (Application in daily life/Making hypothesis)
Answer:
In winter acrylic fabrics are more comfortable. Because acrylic gives warmth to our body. Acrylic looks like natural wool. The wool obtained from natural sources is quite expensive, where as clothes made from acrylic are relatively cheap.

Question 10.
The fabrics namely natural, synthetic and blended are available for garments. Which fabrics will you prefer to wear for rare occasions like functions and in routine? Why? (Text. P. No. 38)(Daily life applications/Concern to bio-diversity)
Answer:
For functions prefer natural garments because they look very rich and comfortable. I also prefer blended garments because they have the best qualities of both fibres. For routine, I prefer synthetic garments. Because they are cheap, long-lasting, durable, readily available, affordable and are easy on maintenance.

Question 11.
Which fabrics do you prefer? Natural or Synthetic? Why? Discuss comparatively. (Text. P. No. 39) (Conceptual understanding/Daily life application)
Answer:
For routine, I prefer synthetic garments because they are cheap, long-lasting, durable, readily available and are easy on maintenance.

Question 12.
What is the difference between washing of clothes at home and washing by dry cleaning at laundry? (Text. P. N’o. 39) (Conceptual understanding/Making hypothesis/Daily life applications)
Answer:
In our home the washing method is same for all types of clothes. We use same type of detergent and washing powder for washing various types of clothes irrespective of laundry label codes.

But in laundry different washing methods are used for different kinds of clothes. Basing the laundry label codes on clothes, they use different detergents, and chemicals for washing different types of clothes.

Question 13.
Certain try pans are said to be non-stick. What made them as non-stick? (Text. P. No. 44) (Conceptual understanding/Applications in daily life)
Answer:
Certain Fry pans are made up of Teflon. Teflon is a non-stick plastic. Teflon is used as a non-stick coating in cookware, So they ate said to be non-stick.

Question 14.
Firemen wear dress which does not catch fire. What type of fabric is it made of?
(or)
Why is it advised not to wear synthetic clothes while working in a laboratory or working with fire. (Making hypothesis is/Daily life applications)
Answer:
Firemen wear dress made with fireproof plastic%. The synthetic fibre melts on heating. If the cloth catches fire it can be very disastrous. The fabric melts and sticks to the body of the person wearing it. So it is therefore advised not to wear synthetic clothes while working in a laboratory or working with fire. For these reasons, human beings prefer for the alternative for natural fibres.

TS 8th Class Physics 2nd Lesson Friction Activities

Activity -1:
Identify household articles made up of natural and synthetic fibre: (Text. P. No. 32)

Question 1.
Look around you and prepare a table with articles made up of natural and synthetic fibre. (Project work/Conceptual understanding)
Answer:

Source	Articles
Natural fibres from plants	Chair, table, cotton dress, jute bag, pencil, paper.
Natural fibres from animals	Woollen clothes.
Synthetic fibres	Plastic containers carry bags, pen, polyester clothes, electric switches, combs, toys, kitchen wares

Activity -2: Beads and paper clips Dattern: (Text. P. No. 33)

Question 2.
How do you explain the structure of Polymer’ with the help of bead or paper clips? (Experimentation)
Answer:
Take some bead or paper clips and Join them together. Observe the structure formed.
Single units of beads or paper clips can be joined together to form a long chain-like structure. Each bead or dip is a separate unit but when many such units are joined, they form a new, different structure.

Similarly, synthetic fibres are also chains of small units joined together. Many small identical units combine to form a large unit called polymer. The small units are called monomers. Synthetic fibres are made of polymers.

Questions based on the above Activity – 2
a. What does polymer mean? (Conceptual understanding)
Answer:
‘Poly’ means many and ‘Per means part or unit. The word is derived from Greek. So polymer is a structure made up of many small repeating units.

Activity -3: identifying fibres – burning test: (Text. P. No. 34)

Question 3.
How do you Identify the fibres with burning test or flame test? (Experinientation/ Project work)
Answer:
I will identify the libres, by conducting burning test to different arts and conduce that

• If it smells like burning hair, the yarn is wool or silk.
• If it smells like burning paper, the yarn may be cotton or rayon.
• If the yarn melts in the flame, it is a synthetic Fibre such as nylon and acrylic.

Activity -4: How strong Is nylon: (Text. P. No. 35)

Question 4.
How do you find the strength of a fibre? Explain an activity and find out which Is the strongest fibre. (Experimentation/Project work)
Answer:

• Take an iron stand with a clamp.
• Take cotton, wool, nylon and silk thread about 50cm in length. Note that all the threads should be of the same length and almost of the same thickness.
• Tie a cotton thread to stand, and at the free end suspend a pan so that weight can be placed on it.
• Add weight one by one till the thread breaks. Note down the total weight required to break the thread.
• Repeat the same activity with threads of wool, silk and nylon. Find out the total weight required to break each thread.

Type of thread	Total weight fibre required to break
1. Cotton
2. Wool
3. Silk.
4. Nylon.

vi. From the above activity, you find the nylon thread is stronger than others.

Activity -5: (Text. P, No. 37)

Question 5.
Why we combine fibres?
Answer:

1. Visit a nearby garment shop and look at the labels on the clothes (figure).
2. Record the percentage of different fibres mentioned on labels.
3. You may find rayon mixed with wool and cotton, polyester is mixed with cotton and wool. Even Nylon is mixed with polyester.
4. Natural and synthetic fibres are often blended for preparing better fabric.

Activity -6: How can you say a bottle is PET bottle: (Text. P. No. 40)

Question 6.
How can you say a bottle is PET bottle? (Field investigation/Making hypothesis/ Conceptual understanding)
Answer:
collect different kinds of water bottles and look at them carefully, You observe a triangle-shaped symbol at the bottom of the bottle or on the brand label slicker.

If ‘1’ number is in the centre of the triangle, then it is a PET bottle.

a. Draw the different Resin Identification codes and Explain the symbols. (Drawing/Daily life application/Comment the diagrams)
Answer:

1. Polyethylene Terephthalate (PET, PETE)
2. High-Density Polyethylene (HDPE)
3. Vinyl (Poly Vinyl Chlonde or PVC)
4. Low-Density Polyethylene (LDPE)
5. Polypropylene (PP)
6. Polystyrene (PS)

other (The category of “other” includes any resin not specifically numbered 1, 2, 3, 4, 5, or 6, or combinations of one or more of these resins.)

Activity-7 (Text. P.No. 40)

Question 7.
Identification of various articles with recycling codes.
Answer:
1. Collect bottles of soft drinks (500 ml or more), bottles of juice, and containers of fruit jam, Ketchup, shampoo, Boost or Bournvita and try to look for the triangle.
2. First look at the soft drinks and juices. You may observe that irrespective of the brand name, the number 1 is marked in the middle of the triangle.

3. It indicates that it is a PET bottle.
4. In the same way other objects are also identified by recycling codes given below.

Activity -8: (Text. P. No. 42)

Question 8.
How do you identify the thermoplastic and thermosetting plastics? (Experimentation/Field Investigation/Making hypothesis)
Answer:

1. Take two bottles made up of plastic. One is Tupperware and another ordinary.
2. Pour some hot water in both the bottles. Observe what will happen?
3. Plastics which get deformed easily on heating are known as thermoplastics.
4. Some plastics, which moulded once cant be softened by heating are called as thermosetting plastics.

Activity – 9: Biodegradable – Non-biodegradable (Text. P. No. 46)

Question 9.
How do you know whether the substance Is biodegradable or non-biodegradable? (Project/Experimentation)
Answer:

1. Take peels of fruits and vegetables, leftover foodstuff, waste paper, cotton cloth and plastic bag.
2. Keep this material in a pit. List the material which remains for a long time and those that disappear quickly.
3. By observing the time taken for the decomposition of the substances, classify them into bio-degradable and non -biodegradable.

Type of waste	Approximate time	Degradable/ non degradable
Peels of fruits and vegetables	1 to 2 weeks	Degradable
Leftover foodstuff	1 to 2 weeks	Degradable
Waste paper	10 to 30 days	Degradable
Cotton cloth	2 to 5 months	Degradable
Plastic bag	Several years	Non – degradable

Lab Activity

Question 1.
How do you identify the thermoplastic and thermosetting plastic? (Text. P. No. 42)
Answer:
Aim: Identifying thermoplastic and thermosetting plastics by flame test.
Materials Required: Tong.. spirit lamp, samples of plastics (Collect small pieces of plastics from the objects like comb, toothbrush handle, plastic bucket, handle of utensil, and electric switch, piece of melamine of meals plate and coffee mug)

Procedure:

1. Take a spirit lamp and light it
2. Clamp one piece of plastic sample say piece of toothbrush with tong.
3. Made the sample on spirit lamp flame.
4. Observe the changes during the burning of sample.
5. Note your observations like whether sample are being softened or burnt with smell or become hard etc.
6. Repeat procedure with other samples.
7. Record your observations sample wist in the following table.

a. Collect small pieces of plastic from some object and conduct a flame test. Record the observations and classify them into Thermoplastic/Thermosetting plastics. (Project work/Expethnentation)
Answer:

Name of the Plastic sample	softened/become on heating	Thermoplastic/Thermosetting plastic
1. Toothbrush handle	Softened	Thermoplastic
2. Comb	Softened	Thermoplastic
3. Piece of bucket	Softened	Thermoplastic
4. Handle of utensil	become hard	Thermosetting plastic
5. Electric switch	become hard	Thermosetting plastic
6. Meals plate	become hard	Thermosetting plastic
7. Coffee mug	become hard	Thermosetting plastic

TS Board Telangana SCERT Class 8 Physics Solutions 2nd Lesson Friction Textbook Questions and Answers.

TS 8th Class Physics 2nd Lesson Questions and Answers – Friction

Reflections on concepts

Question 1.
Explain the types of fractions with suitable examples?
Answer:
I know four kinds of frictions. They are Static Friction: When a force is applied to an object hut it does not cause it to move. Example: pushing on a wall.
Fluid Friction: Occurs when a object moves through a fluid, meaning either a liquid or gas. Example: sky diving, swimming.
Sliding Friction: Occurs when solid surfaces slide over each other.
Example: falling on the pavement.
Rolling Friction: Occurs when an object rolls over another (something with wheels or that is circular like a ball)
Example: riding a motorcycle.

Question 2.
A book placed on the surate of table. The book is pushed in one direction. Draw the forces acting on the book and explain.
Answer:

1. A book is placed on a table.
2. It is slowly pushed.
3. The book gets some speed in the direction of the push.
4. The book slowly decreases between the table finally stops. rushing the book.
5. Here the frictional force between the table and the book opposes the motion of the book.
6. The book finally stops because of this frictional force.
7. The weight of the book balances with normal reaction. Therefore there is no vertical moment for the book.
   W-N=O
8. Along Horizontal direction frictional force opposes the pushing force. The Net resultant force between these to make the book to move.

Here W = Weight of the book
N Normal reaction
F = Pushing force
f = Frictional force
Here W = N
No vertical motion for this book.
The Net force with which book moves is Net Force = F – f

Question 3.
Give few examples for sliding.
Answer:
Examples for sliding friction:
1. Skating on the snow
2. Stop the vehicles by applying brakes because of sliding friction between road and tyres of the vehicles.
3. We are able to write with pencil on a paper or with a chalk on blackboard because of sliding friction.

Question 4.
Explain how does lubrication reduce friction.
Answer:
When oil or grease (lubricant) is applied between the moving parts of a machine, a thin layer is formed between the moving surfaces and hence they do not directly rub against each other. The interlocking of irregularities is avoided to a great extent. Hence friction decreases and movement becomes smooth.

Question 5.
Explain with one example that Frictional force ¡s proportional to the Normal force.
Answer:

1. Connect a brick to Spring balance and measure the frictional force. It is nothing but reading of the Spring balance.
2. Now add another brick to the first one.
3. That means weight of the body is increased.
4. We can observe that the frictional force also increases.
5. Since we know that weight and normal reaction are equal. We can say that Frictional Force ∝ Normal Force.

Application of concepts

Question 1.
Explain why do sportsmen use shoes with spikes.
Answer:
Sportsmen use shoes with spikes. Because spikes provide the shoes better grip on the ground.

Question 2.
Would it be easier or difficult for you to walk on a marble floor with soapy water. Why?
Answer:
It is very difficult to walk on a soapy floor because soapy floor creates very less friction comparing with normal floor. So we can slip on such soapy floors.

Question 3.
What happens if we do not reduce friction in machines?
Answer:

1. In machine parts friction must he less for the free movement of them.
2. In order to reduce friction we need to apply some lubricating oil. Eg: Lubricating oil is applied in the motors, rollers, cycle pedals etc.
3. If we do not reduce the friction the wear and tear of the machine parts comes quickly and finally they will not move because of friction.

Question 4.
What purposes are surved by using bearings in machines? Explain with daily life examples.
Answer:

1. Bearings are used in Fans, Cycle Pedals, Skaters, etc.
2. Since the Bearings are spherical there is only rolling friction which is very less.
3. When we use these bearing the movement of the wheels are very free.
4. When we do not use these bearings it will be very difficult for the wheels to move.
5. Nowadays in sewing machines, pedestal fans, sofa sets also they are attaching wheels at the bottom so that we can move them freely. The wheels at the bottom are fixed with ball bearings.
6. It is always easier to pull the luggage fitted with rollers.

Question 5.
Draw a free-body diagram (FBD) to show various forces acting on a body which is sliding on an inclined plane.
Answer:

N – normal force
W – weight of the body
f – friction force

higher Order Thinking Questions

Question 1.
Do you agree with the statement Hfriction is both good and evil?’ Explain with examples.
Answer:
Friction is both good and evil.
I. Friction is good :

• Friction allows us to walk or run without slipping.
• Friction allows vehicles to travel on the road safely.
• To slow down or stop the vehicle we use brakes which use friction between road and tires of vehicles.
• Friction enables us to hold things with our hands.
• Friction helps us to sharpen a knife or other instruments.
• Friction helps us to fix a nail in the call.
• No building can be constructed if there is no friction.

II. Friction as an evil :

• Friction causes wearing and tearing the surfaces which are in contact.
• Friction causes worn-out the tires, which are dangerous because they can slide and skid easily.
• Friction produces heat in machine which can damage some parts of the machine.
• Friction also produces static electricity which is dangerous.
• Friction also causes wasting of energy and fuels.

Question 2.
Reducing friction to the lowest possible level in machine tools solves the problem of energy crisis and conserves biodiversity. How do you support the statement? Explain.
Answer:
If friction is more in machine tools, more fuel is consumed. This led to the wastage of fuel and causes energy crisis. If energy crisis formed, biodiversity in nature was damaged. So, reducing friction to the lowest possible level in machine tools solves the problem of energy crisis and saves the biodiversity.

Question 3.
Explain why sliding friction ¡s less than static friction.
Answer:
The interlocking of irregularities in the two surfaces which in contact causes friction force. When the object starts sliding the contact points on its surface do not get enough time to lock into the contact points on the floor (or other objects). So sliding friction is less than static friction.

Question 4.
Scientists designed the shape of aeroplane using the technique of reducing fluid friction by observing birds’ shape. How would you appreciate it?
Answer:

1. It is obvious that when objects move through fluids, the have to overcome friction acting on them.
2. In order to minimize the friction objects are given special shapes.
3. Scientists after observing the birds and fishes they thought of designing the aeroplanes in these shapes.
4. Birds and fishes have to move about in fluids all the time.
5. Their bodies must have evolved to shapes which would make them not to lose much energy in overcoming the friction.
6. The aeroplanes are made in this ship because they experience more drag and move freely.
7. They consume less fuel to fly in air, so as birds use less energy in overcoming the fluid frictional force.

Multiple Choice Questions

Question 1.
Which material do gymnasts apply on their hands to increase friction for better grip [ ]
a) Oils
b) Soap
c) Coarse substance
d) water
Answer:
c) Coarse substance

Question 2.
The relation between the change in the length of spring and the applied force is [ ]
a) Inversely proportional
b) Equal
c) Directly proportional
d) Never depends on the force
Answer:
c) Directly proportional

Question 3.
The bodies of birds and fishes must have evolved to shapes which would make them not to loose much energy in overcoming [ ]
a) Rolling friction
b) Static friction
c) Sliding friction
d) Fluid friction
Answer:
c) Sliding friction

Question 4.
Which of the following friction has self adjusting force [ ]
a) Sliding friction
b) Static friction
c) Rolling friction
d) Fluid friction
Answer:
b) Static friction

Suggested Experiments

Question 1.
Conduct an experiment to understand the nature of fiction and the concept of Static friction.
Answer:
Nature of friction and concept of static friction:
The faite which opposes the relative motion altivo surfaces of bodies in contact is called frictional force.
Static friction is the friction which comes into play when surfaces of the objects are at rest relative to each other.

Eg:

1. Push a heavy box which is kept on a floor with small force.
2. The box does not move because frictional force is equal to the applied force.
3. Even if applied force is increased the box still does not move, because the frictional force also increases which balances with applied force. So we can conclude that static frictional force is self-adjusting force.
4. After crossing the limit of static friction if the applied force is increased the box starts to move. Here the applied force crossed the limit of static friction.

Question 2.
Conduct an experiment to find out the effect of roughness on frictional force.
Answer:

1. A surface is said to be smooth surface if there are no irregularities.
2. A surface is said to be rough surface if there are some irregularities.
3. Lake an inclined smooth plane
4. Allow a pencil or pen or dIl other rolling body to roll down on it.
5. Find the distance travelled  the pencil on it
6. Repeat the same experiment on rough inclined plane
7. once again find the distance travelled by the object on rough inclined plane
8. It is observed that the distance travelled by the object on smooth inclined plane is more than on rough inclined plane
9. so we can conclude that the irregularities on a surface increases the frictional force which opposes the motion of the body.

Suggested Projects

Question 1.
Collect information about various new techniques being adopted by human beings to reduce energy losses due to friction. Prepare a report on it.
Answer:
Methods of Reducing Friction: there are a number of methods to reduce friction in which some are discussed here.
Use of Lubricants : (Cycle and door): The parts of machines which are moving oven one another must be properly lubricated by using oils and lubricants of suitable viscosity.

Use of Ball Bearings: In machines where possible, sliding friction can he replaced by rolling friction by using ball hearings.
Design Modification: Friction can he reduced by changing the design of fast-moving objects. The front of vehicles and airplanes made oblong to minimize friction.

Question 2.
Collect information about the substances using to reduce the friction in different machines and prepare a report on it.
Answer:
Methods of Minimising Friction:
Polishing: Friction in machines decreases by means of polishing the machine parts moderately.
Using Ball bearings: By using Ball bearings in rolling parts of the machines the frictional force decreases.
Using Lubricating Oils: Using Lubricating Oils like ‘2T’ oil, machine oil, etc. we can reduce the frictional force in machine parts. The machine parts will more freely.
Aerodynamic Model: Automobiles are manufactured in aerodynamic shape to reduce the friction due to fluid.

TS 8th Class Physics 2nd Lesson Friction Intext Questions

Think and discuss

Question 1.
Does friction oppose motion or relative motion of surfaces in contact? Discuss. (Tnt. P. No. 22) (Conceptual understanding)
Answer:
Relative motion

Question 2.
What observations and experiments can you cite to show the existence of friction? (Field investigation/ Experiments/Daily life applications)
Answer:
The following observations and experiments show the existence of friction.

• Fan comes to rest after switched off because of friction.
• Heat is produced, when two hands rubbed vigorou%Iv, because of friction.
• Marble from a inclined plane comes to stop after some distance on the horizontal floor because of friction.
• Wearing and tearing of machinery parts and shoes was because of friction.

Question 3.
When do we speak of sliding friction? (Text. P. No. 23) (Making hypothesis)
Answer:
Sliding friction comes into p1a when an object is sliding over another.

Question 4.
Does friction act on a table resting on the floor? (Text. P. No. 25) (Making hypothesis/ Field investigation)
Answer:
No. friction is not acting on a table standing on a floor. When a force is applied on table to move it then friction comes into play. The force applied is balanced by the force of friction.

Question 5.
If normal force is doubled, what happens to friction? Discuss. (laking hypothesis/ Conceptual understanding)
Answer:
Frictional force is proportional to the normal force. i.e., Friction u Normal force. So, if normal force is doubled, then friction ∝ also doubled.

Question 6.
Your friend says “it depends on area of contact’. How can you correct your friend through some experiments? (Communication through drawing, model making)
Answer:
I will correct my friend through the following experiment.

• Tie a string around a brick. Put the brick in horizontal position.
• Pull the brick by using a spring balance.
• Note down the reading of spring balance when brick just begins to move.

• Now turn the brick upright (less area) so that the contact area with the floor becomes small.
• Do the same experiment and measure the friction using spring balance reading.

• The frictional force is same in both cases and irrespective of area of contact of the bodies.
• So the frictional force is independent of the area of contact.

Question 7.
“Fiction is independent of weight, but depends on normal force between surfaces of contact where friction exists”. Do you agree with this statement? Discuss. (Conceptual understanding)
Answer:
Yes. As we increase the weight or applied a force pressing vertically, normal force increases. As normal force increases, frictional force also increases.

Question 8.
What important role does the friction play in the life of human beings and animals? (Text. P. No. 26) (Daily life applications/Field investigations)
Answer:

• Friction helps for human beings and animals for safe walking on the floor or ground.
• Friction is helpful to hold objects.
• Friction is helpful for animals for climbing trees and rocks.

In this way friction has played important role in the life of human beings and animals for getting food, walking and also for survival.

Question 9.
Why Is friction important for transport? (Daily life applications)
Answer:
Friction is important for transport because vehicle moves safely on roads due to friction. Tires of vehicles grooved. Grooves increase friction. This helps easy rolling of vehicles on the road. Boats and ships are also able to move through water because of friction. From these we conclude that friction is important for transport.

Question 10.
Can we reduce friction to zero? Explain. (Text. P. No. 28) (Making hypothesis /Conceptual understanding)
Answer:
Friction can never be entirely eliminated, No surface is perfectly smooth. Some irregularities are always there.

Question 11.
What purposes are served by bearings in machines? Explain with daily life situations. (Intonation skills/Conceptual understanding)
Answer:
To reduce friction between the rotating shafts of machine tools, we use ball bearings. In our daily life we use the fan to give air and cycle to go anywhere. Ball bearings will be used in both of them.

TS 8th Class Physics 2nd Lesson Friction Activities

Activity – 1:
Identifying forces acting on a body and effect of frictional force: (Text. P. No. 19)

Question 1.
How do you Identify forces acting on a body and effect of frictional force? (Field investigation/Experimentation)
Answer:
i) Gently push a book on a horizontal floor. Then the book acquires a certain speed in the direction of push. However the speed of the book gradually decreases and after some time it get stops.

ii) Two forces act on the book in the vertical direction. They are
a) Weight of the book (W) or gravitational force acting vertically down.
b) Normal force (N) or reaction force applied by the table.

The force applied by the table on the book is called frictional force.

Questions based on the above Activity-1

a. Why does the book stop after covering some distance?
Answer:
The frictional force between book and horizontal Floor opposes the relative motion of the book. So the book stops after covering some distance.

b. Why does the speed of the book change gradually?
Answer:
Due to the action of frictional force opposite to the motion of the book, the speed of the book changes gradually.

c. Is the book moving with uniform speed?
Answer:
No, book is not moving with uniform speed. The speed of the book decreases in the horizontal direction that means book travels with deceleration.

d. How many forces are acting on the book when it is pushed on the floor?
Answer:

• Frictional force applied by the floor in the horizontal direction.
• The force used to move the book.

Activity – 2 :
Observing the variation of friction: (Text. P. No. 22)

Question 2.
How do you conclude that friction Is a self-adjusting force? (Experiment/Making hypothesis)
Answer:

Push a heavy box which is kept on a floor F with less force to move horizontally the applied force on the box. Now gradually increase the applied force, the box still does not move, because the frictional force also increases accordingly and balances the increased applied force. From this experiment, we conclude that static friction is a self-adjusting force.

Activity- 3 :
Effect of roughness on frictional force: (Text. P.No. 23)

Question 3.
How do you prove that ‘Roughness effects the frictional force’? (Experiment/Field investigation)
Answer:
Effect of roughness on frictional force:

1. Set up one inclined plane on the horizontal floor.
2. Use a wooden board as inclined plane. Put a mark at any point A’ on the inclined plane.
3. Now lei a marble moves down from this point. Note the distance covered by the marble from the bottom of the inclined plane to point where it comes to stop.
4. Now spread a cloth over the floor. Make sure that there are no wrinkles in the cloth.
5. Do the same with marble and note down the distance. The distance is less when cloth is spread over the floor when compared the distance on the floor without cloth.
6. We can conclude that smoothness/roughness of the surfaces affect the distance travelled by marble.
7. The force of friction is greater for rough surfaces i.e. frictional force increases with roughness of the surfaces.

Questions based on the above Activity-3

a. What are your observations from this experiment?
Answer:
Frictional force increase with the increase in roughness of the surface.

b. In which case the distance is covered maximum?
Answer:
The distance covered by ball when there is no cloth on the floor is maximum.

c. In which case the distance is covered minimum?
Answer:
The distance covered by ball when there is cloth on the floor is minimum.

d. Why is the distance covered by the pencil cell different on different surfaces? Discuss the result.
Answer:
In first case due to lack of cloth on the floor and less frictional force ball covers more distance. In the second case the ball covers less distance when there is a cloth on the floor. Because frictional force is less.

Activity -4: Effect of area of contact in frictional force: (Text. P. No. 24)

Question 4.
How do you prove that the frictional force Is independent of the area of contact? (Expectation/ Field investigations)
Answer:

• Tie a string around a brick. Put the brick in horizontal position.
• Pull the brick by using a spring balance
• Note down the reading of spring balance when brick just begins to move.

• Now turn the brick upright (less area) so that the contact area with the floor becomes small.
• Do the same experiment and measure the friction using spring balance reading.

• The frictional force is came in both cases and irrespective of area of contact of the bodies.
• So the frictional force is independent of the area of contact.

Questions based on the above Activity-4

a. How many forces are acting on the brick in horizontal direction?
Answer:
There are two forces acting on the brick in horizontal direction one is frictional force and the other is applied force.

b. How does the frictional force vary with the change In the area of contact?
Answer:
Frictional force does not depend on the area of contact. So there is no change in frictional force with the change in contact forces of the bodies.

Activity -5: Effect of normal force in friction: (Text. P. No. 24)

Question 5.
Describe an experiment to know the effect of normal force on friction. (Experimentation)
Answer:

1. Tie a string around a brick. Pull the brick by using spring balance.
2. Note down the reading of spring balance when the brick just begins to move.
3. Scale of the spring balance gives directly the applied force in newtons.
4. Now put another brick over the first brick tied to the spring balance.
5. Measure the force of friction by the method described above.
6. From the above activity, we can understand that when we add a brick to the existing brick, it’s normal (once increases and hence frictional force is also increased.
7. So, frictional force is directly proportional to the normal force.

Activity -6
Friction produces heat: (Text. P. No. 25)

Question 6.
Describe some examples where heat ¡s produced due to friction. (Conceptual understanding/Application in daily life)
Answer:
Friction is the force which opposes the relative motion between the two surfaces and can also produce heat.
When we rub our hands together vigorously for few minutes, we feel hotness. When we strike a match stick against rough surface, it catches fire.

Activity -7:

Question 7.
How to reduce friction increasing and decreasing friction: (Text. P. No. 26)
Answer:

1. Take a spoon and how its head in the (broader portion) left hand and hold the mid portion of the spoon by the right hand and pull it towards the other end of the spoon.
2. Now you are noticing here friction increases gradually.
3. Now dip your right-hand fingers in water do it again as said above.
4. Now you are noticing here friction decreases gradually.
5. Thus friction can be advantageous in some cases and disadvantageous in other cases.

Questions based on the above Activity -7

a) Have you ever thought why the sole of your shoes is grooved as shown in figure?
Answer:
The sole of our shoes is grooved because it is done to provide better grip on the floor so that we can move safely.

b) Why do you need to change the lyres when its threading is worn out?
Answer:
We need to change the fires when its threading is worn out because the grip confliction between the tires and road in order to increase efficiency.

Activity- 8:
Effect of rollers on friction: (Text. P. No. 27)

Question 8.
Explain the effect of rollers on friction.
Answer:

• Pull a suitcase without rollers and pull a suitcase which has rollers.
• Try to push a book lying on the table. Now place Pushing a book on pencil the same book on two or three pencils. Push the book again.
• it is always easier to roll a body than to slide it over a surface.
• So rollers are used to reduce frictional force.

Activity -9:
Understanding the principle of ball bearings (Text. P. No. 28)

Question 9.
Explain the principle of ball bearings with an activity. (Field investigation)
Answer:

• Take two lids and rotate them by putting one on the top of the other.
• Now place two or three marbles on one lid and place the other lid on the top of the marbles.

 

• Now try to rotate the top lid. Comparing in the first case it is easy to rotate the lid in the second case.
• From the above experiment (activity) the principle of ball bearing is to reduce friction between the rotating shafts of machine tools, we use hail bearings. Ball bearings convert the sliding friction into rolling friction.

Activity – 10 :
Observing the fluid friction: (Text. P. No. 28)

Question 10.
How do you say that fluids exert force of friction on objects in motion through them? (Experinensation/ Field investigation)
Answer:

• Take a glass of water and stir it with a spoon.
• Water whirls around in glass stop stirring and observe.
• The whirling speed of water gradually decreases and after some time, the water stops whirling and comes to stable state.
• Because of the frictional forces between the liquid layers or between the liquid surfaces that is in contact with glass surface are responsible for stopping the rotation of the water.
• From the above experiment, we conclude that water and other fluids exerts force of friction on objects move through them.

Questions based on the above Activity – 10

a. Which force is responsible for stopping the rotation of the water?
Answer:
Due ro frictional force between the layers of surface of liquid and surface of glass water comes to rest.

Activity – 11 :
identifying factors influencing the fluid friction: (Text. P. No. 29)

Question 11.
Conduct an activity to show the factors influencing the fluid friction.
Answer:

• Take a tub of water. Trw to move your hand in water in the direction of fingers stretched.
• Now try to move your hand in the direction perpendicular to the open face of the hand.
• In second case (perpendicular to the open face) you feel more frictional force. (drag)
• From this we conclude that the frictional force on an object in a fluid depends on its speed with respect to fluid and on the shape of the object and nature of the fluid.

Lab Activity

Question 1.
Explain an activity to understand the nature of frictIon and the concept of static friction. (Text. P. No. 20) (Experimentation)
Answer:
Aim: Understanding nature of friction and the concept of static friction.
Material required: Toy trolley, small wooden block, inextensible string, weight hanger, weights pulley, and table.

Procedure: Take a small toy trolley and keep a small wooden block on it as shown in fig. Tie an inextensible string to the trolley and pass it over a pulley. And other end of the string is fixed to weight hanger. Take a small weight and keep it on weight hanger and observe the changes in motions of block and trolley.

1. Take a small toy trolley and keep a small wooden block on it as shown in the figure.
2. Tie an inextensible string to the trolley and pass it over a pulley.
3. Other end of the string is fixed to weight hanger. Take a small weight and kept it on weight hanger and observe the changes in The trolley accelerating left motions of block and trolley.
4. You may notice that the trolley with the block moves towards left with an acceleration.
5. The block is at rest with respect to the surface of the trolley, but it is in motion with respect to the surface of the table.
6. If you increase the weight on the hanger, the surface of the trolley tries to keep the block at rest with respect to its floor.
7. If we increase trolleys acceleration gradually, at certain limiting acceleration or limiting weight. the block comes into motion in the reverse direction.
8. Now there exists relative motion between the surface of the trolley and the block.

Friction: The force which opposes the relative motion of two surfaces of the bodies which are in contact is called frictional force.

TS Board Telangana SCERT Class 8 Physics Solutions 1st Lesson Force Textbook Questions and Answers.

TS 8th Class Physics 1st Lesson Questions and Answers – Force

I. Reflections on concepts
Question 1.
What is a force? What changes can be produced by a force?
Answer:
Force is a push or a pull. It Is an external cause which changes or tends to change the state of rest or motion.

• Force can change the shape of an object.
• Force can change the speed of motion.
• Force can change the direction of motion.
• Force can change the state of motion or rest.

Question 2.
Give two examples each for a contact force and a force at a distance.
Answer:
Contact force: Force is being applied by actually touching the body is called constant force
Eg:

• Muscular force
• Frictional force,

Noncontact force (or) Force at a distance: Force is being applied without touching the body is called non contact force or force at a distance.

Eg:

• Gravitational force,
• Magnetic force,
• Electrostatic force.

Question 3.
Explain Gravitational Force by giving a suitable example.
Answer:
Definition: The force exerted on a vertically projected body by earth is called gravitational force. Because of this force, only the body falls down to the ground.

Explanation:

1. Every object on the earth or close to earth will experience a gravitational pull.
2. This force of attraction exists between two bodies everywhere in the universe.
3. Since earth is having more mass all the bodies which are close to the earth are attracted towards it.
4. We cannot experience the gravitational force that exists between two persons and person with any table or blackboard because ills very small.

Eg:

1. The force between teacher and student in the classroom.
2. The force between student and blackboard.
3. The force between Earth and Moon.
4. The force between any two heavenly bodies.

Question 4.
Draw and explain a free-body diagram (FBD) to show all the forces acting on a car.
Answer:
Here Force F Applied by the Engine.
f = Frictional force applied by the road.
N₁ and N₂ ⇌ Normal forces
W → Weight of the car or Gravitational force.
The Net resultant force in vertical direction
F_net = N₁ + N₂ – W
The Net resultant force along Horizontal force. N,
F_Ne = F-f

Question 5.
Why do tools meant for cutting always have sharp edges?
Answer:
The effect of force depends on the area of contact on which the force is acting. When there is a decrease in the area of contact of the force or load then the effect of force increases and vice versa. So the tools meant for cutting always have sharp edges to acquire maximum effect of force.

Application of concepts

Question 1.
How can you differentiate between a contact force and a force at a distance?
Answer:

Contact force	Force at distance
1. Force is being applied by actually touching the body Eg: Muscular force, Frictional force.	1. Force is being applied without touching the body. Eg: Gravitational force, Magnetic force.

Question 2.
Find the net forces from the following diagrams.

Answer:
a) Total force from left to right = 10 + 8 = 18 N
Force from right to left = 12 N
Net force = 18-12 = 6 N from left to right.

b) Force from left to right = 8 N
Force from right to left = 8 N
Net force = 8- 8 = 0 N

c) Total force from left to right 8 + 6 14 N
Force from right to left = 0 N
Net force = 14 – 0 = 14 N from left to right.

d) Force in upward direction = 9 N
Force in downward direction = 8 N
Net force = 9 – 8 = 1 N in upward direction.

Question 3.
A man stand still on a level floor. What forces will act on him? Draw a free-body diagram (FBD) to show all forces acting on him.
Answer:
Two forces acting on a man standing on a level floor.

W – Weight (Gravitational force) 4, N Leri low
N- Normal force.

Question 4.
The surface area of an object is 20 m² and a force of 10 N is applied on it then what is the pressure?
Answer:
Pressure = \(\frac{\text { Force }}{\text { Area }} \)
P = \(\frac{F}{A}\)
P = \(\frac{10}{20}\)
= \(\frac{1}{2}\) = 0.5 N/m² or Pascal.

Question 5.
How do you appreciate the role of friction In facilitating our various activities?
Answer:
If there is no friction between any two surfaces in contact, then the present day civilization will be no more as we cannot even walk property on the ground. There will be no fabrics and garment, no construction of buildings and no future, even no fire for cooking and no vehicles. So friction is very necessary in our daily life. So, I appreciate the friction for its facilitation to us for doing various activities in our daily life.

Higher Order Thinking Questions

Question 1.
If you push a heavy box which is rest, you must exert some force to start its motion. However, once the box is sliding, you apply a lesser force to maintain that motion. Why?
Answer:
When a heavy box is at rest there is maximum frictional force between box and surface. So maximum force is used to move that box. Interlocking of irregularities in the two surfaces which are in contact cause friction force. When the box starts sliding, the static friction converts into sliding friction, which is less than static friction. So we need smaller force to maintain that motion.

Question 2.
Karthik Is observing the live telecast of a one-day cricket match. He noticed that motion of a roller on the pitch during lunch break. He thought about various forces acting on the roller and the net force when It is in motion. Many questions arose ¡n his mind regarding the direction of the net force. Can you guess what would be those questions?
Answer:
I think the following questions will be raised in his mind regarding the direction of the net force of the moving roller.

• Why does the roller move when it is pushed?
• What is the net force acting on the roller when it was pushed?
• What are the forces acting on the roller when it moves?
• Does the motion of the roller depend on the roughness and smoothness of the ground or not?

Question 3.
How do you increase the pressure by keeping (a) area unchanged and (b) force unchanged?
Answer:
We know that force acting on a unit area of a surface is called pressure.
Pressure = \(\frac{\text { Force }}{\text { Area }}\)
I will change the pressure by keeping —
area unchanged: If force acting on the same area of surface, the pressure also increases. So we can change the pressure by changing the force acting on that surface.
Pressure ∝ Force.
force unchanged: By increasing or decreasing the contact area or surface area on which the force is acting, there will be change in pressure acting on it without changing the force.

If the surface area is smaller the pressure will be greater and vice versa.
Pressure ∝ \( \frac{1}{\text { Area }}\)

Question 4.
Imagine that friction disappeared from the earth. What will happen? Explain.
Answer:
If the friction has disappeared from the earth.

1. We will not be able to walk or run on the ground.
2. Vehicles will not move if they are in rest. Vehicles will not stop if they are in motion.
3. We will not be able to hold the things.
4. Accidents will occur if there is no friction.
5. Without friction, no building could be constructed.

Multiple Choice Questions

Question 1.
Hoisting a flag is related to ( )
A) push
B) pull
C) Push and pull both
D) pressure
Answer:
B) pull

Question 2.
A person is pulling water from well. Which type of force it is ( )
A) Muscular force
B) Magnetic force
C) Friction force
D) Electrostatic force
Answer:
A) Muscular force

Question 3.
The force that a solid surface exerts on any object in the normal direction is called ( )
A) Muscular force
B) Normal Force
C) Tension force
D) Magnetic force
Answer:
B) Normal Force

Question 4.
let the forces F1 and F2 act on the table in opposite directions F₁ > F₂, the F_net = ( )
A) F₁ – F₂
B) F₁+F₂
C) 0
D) 2F₂ – F₁
Answer:
A) F₁ – F₂

Question 5.
A situation for effect of force leads to a permanent change in shape of object is ( )
A) Stretching Rubber band
B) Squeezing sponge
C) Spring
D) Breaking glass
Answer:
D) Breaking glass

Suggested Experiments:

Question 1.
Conduct an experiment to find the limiting forces that can be borne by different strings.
Answer:
Aim: To find the limiting force that can be borne by a string.
Material used: Spring balance, weights, light strings, weight hanger.

Procedure:

1. A spring balance is suspend from rigid support.
2. To it a weight hanger is connected.
3. Slowly increase the weights in the weight hanger in steps of 50 grams and note the readings of spring balance.
4. Repeat this experiment till the string breaks.
5. Repeat the experiments with various strings and find out the limiting force of each wire.

Question 2.
Design and conduct an experiment to test few ways how Friction may be reduced.
Answer:

1. Take a thick – heavy book. Push it on the surface of a table. You observe that book moves slowly with the force and covers a small distance.
2. Now take three pencils. Place them parallel to one another on the table and place the book over them.
3. Push the book again with the same force. The book moves a larger distance over the rolling pencils. Rolling pencils reduce the friction.
4. In this way we can reduce the friction by using rollers.

Question 3.
Conduct an experiment to determine the change in effect of force with an area of contact.
Answer:

1. We know pressure = Force/Area and Its ST unit is N/ met² (or) Pascal.
2. Take a pencil. and push its rounded end on %roUr palm.
3. Now push from the other side of the pencil gently so that sharp end is on your palm.
4. We notice that the effect of force depends on the area of contact on which force is acting.
5. When there is decrease in area of contact force, or load then the effect of force Increases and vice versa.
6. ln case of porters keeping luggage on Turbance, School bags straps have more width are some more examples where the force depends on area of contact.

Suggested Projects

Question 1.
Collect pictures to illustrate contact forces, force at a distance and prepare a report.
Answer:
Contact forces:

Forces at a distance:

Question 2.
Classify the actions In your daily life into
i) actions where we exert force which appears as a push
ii) actions where we exert force which appears as a pull
iii) actions which involve both push and pull
Answer:
i) Pushing a heavy ooden table.
ii) Hoisting a Flag
iii) Erasing Blackboard with duster.

Question 3.
Observe the situations of electrostatic forces in your daily life and prepare a report.
Answer:

1. When we keep our hand, near TV monitors, when TV is playing the hairs odour hand are attracted towards the monitors.
2. When glass rod is rubbed with silk cloth glass rod get positive charge and silk gets negative charge.

TS 8th Class Physics 1st Lesson Force Intext Questions

Think and discuss

Question 1.
A book placed on a table is at rest. Is the force of friction acting on it or not? Explain.
Answer:
When the book is at rest, there is no frictional force acts on it, because frictional force comes to play when we try to move it. But a normal force acting on book acts in upward direction by the table.

Question 2.
A system of two bodies A and B are placed as shown in figure. How many forces are acting on A and B respectively?
Answer:
The forces acting on A:

1. Gravitational force (Downward direction)
2. Weight of B (Downward direction)
3. Normal force by floor (Upward).

The forces acting on B:

1. Gravitational force (Downward)
2. Normal force by A (Upward direction)
3. Normal force by floor (Upward)

Question 3.
Why it is necessary to separate a contact force into a normal force and a frictional force? Give at least two reasons.
Answer:
It is very useful to separate a contact force into a normal force and a frictional force. It is useful to calculate the net force acting on the body. To calculate the minimum force required to move a body.
Eg: If a body is at rest means normal force and frictional force are equal and opposite. You have to use force which is more than the frictional force, If it is frictional force, N is normal force and F is the applied force.
F_net = F = f (X-axis direction)
F_net = N = w (Y-axis direction)

Question 4.
A cricket ball of mass ‘m’ is thrown upward with some initial speed. If the air resistance Is neglected, what forces are acting on the ball when it reaches
(a) half of its maximum height and
(b) Its maximum height?
Answer:
a) When the ball reaches half of its maximum height three forces acting on it.

• Force of push acting upward.
• Friction force by air surrounding the ball.

b) When the ball reaches its maximum height two forces acting on it. Normal force or frictional force by air.

Question 5.
two Identical bars, in which one is steel and the other Is a magnet, are painted with same colour. How can you tell which one Is magnet by using only these two bars?(don’t break the bars)
Answer:
If you freely suspend the bars, the magnets come to rest in North-South direction. The steel bar comes to rest in any direction. In this way we can identify the magnet.

Question 6.
Play arm wrestling with your friend. How can you explain the winning of the game by using the concept of net force? Name forces acting on arm and their direction while playing the game. Try to draw FBD for this situation. What forces can do?
Answer:
We know that if two forces act in opposite directions the net force is equal to the difference between the two force. In arm wrestling game, if the two opponents apply same force none of them can move out of the ring.

If one of the opponent’s forces is more than the second one, second person moves out from the ring, then the first person is the winner. If first person is thrown out from the ring by second person, then the second person is the winner. Here the net force acts in the direction of the force applied by the winner.

Question 7.
Does pressure have direction? Explain.
Answer:
Pressure has both magnitude and direction.
Pressure = \(\frac{\text { Force }}{\text { Area }} \)
Since force has direction, pressure also has direction.

TS 8th Class Physics 1st Lesson Force Activities

Activity – 1:
Identiing Dush or pull: (Text. P. No. 1)

Question 1.
“Observe the following table and identify the actions involving push or pull or both. (Conceptual understanding/Information Skills)

a) List three more activities where we exert force which appears as a push. (Conceptual understanding)
Answer:
1. To move the car which is at rest we apply force which appears as a push from back side of the car.
2. We push the table to move front.
3. To close the door we use push as a force.

b) List three more activities where we exert force as a pull. (Conceptual understanding)
Answer:
1. To lift the water from well we use pull as force.
2. To open the door we use pull as a force,
3. We pull the thread of the bow to release an arrow.

c) State three actions which involve both push and pull. (Conceptual understanding)
Answer:
1. To make chapati we use both pull and push on rolling pin.
2. We use both push md pull in ironing the clothes.

Activity -2:
Preparing a list of examples for muscular force: (Text P.No.3)

Question 2.
List at least ten activities where we apply muscular force to perform various tasks. (Information skills and Projects)

Activity where we apply muscular force

1. Lowering a basket

2. Brushing

3. Bathing

4. Eating

5. Driving

6. Walking

7. Lifting the school bag

8. Writing

9. Cutting vegetables

10. Playing

a. Do you feel your muscles get tightened while performing any physical activity? What could be the reason for it?
Answer:
The muscles which are at backside of shoulder will contract if we throw an object to front. In the same way when we lift an object then also our muscles contracted. If we stress a smooth ball with our palms then also muscles tightened it.

Activity -3:
Observing the changes in any muscle while working:

Question 3.
Discuss an activity to observe the changes in any muscle while working. (Experimentation/Application to daily life)
Answer:
Muscles are normally arranged in opposition so that as one group of muscles contract or shortens, another group relaxes or lengthens. For example if you throw a ball the muscles in the chest and front of the shoulder contract to pull the arm forward, while the muscles in the back and rear of the shoulder also undergo contraction to slow the motion down to avoid injury. This shows that our muscles undergo some changes while working.
a) Why does the ball stop?
Answer:
The frictional (once between ball and floor opposes the motion of the ball. That is why ball stops after traveling some distance.
b) Is there any hidden force which brings it to stop?
Answer:
Yes, frictional force helps the ball to stop.

c) Why does the speed of bicycle decrease gradually? (Application to daily life, concern to biodiversity)
Answer:
The speed of bicycle decreases gradually because there is frictional force between lyres and road which opposes the motion of the bicycle.

d) Is there any force acting on It which tends to slow down its speed?
Answer:
Yes, there is frictional force on it which tends to slow down its speed

Activity -4: Observing the motion of a ball on different surfaces:

Question 4.
Roll a ball on different surfaces and observe the motion of ball discuss your observation. (Field investigation/ Experimentation/Making hypothesis)
Answer:
Take a ball. Try to roll the ball on different surfaces like carpet, rough roads, smooth floor etc. The motion of the ball is different on different surfaces. The force offering resistance seems to be more on the rough surfaces than on the smooth surfaces. From this we conclude that fractious force depends on the nature of surfaces which are in contact.
a) If we roll a ball on different surfaces like carpet, rough, roads, smooth or etc then on which surface ball rolls farther?
Answer:
Bail travells more distance on smoother surfaces. The frictional force which opposes the motion of the body is less on smoother surface.

Activity-5 :
Observing the motion of objects in an inclined Diane

Question 5.
Write your observation while moving different objects move on inclined planes. (Experimentation)
Answer:

• Take a tray. Place a small ice cube, eraser, and a rupee coin to stay in line on one end of the tray.
• Now slowly lift this end of the tray as shown in the figure. It forms an inclined plane.
• If you observe, ice cube moves lastly on the inclined plane, then one rupee coin, and finally eraser, move slowly.
• From the above experiment, we conclude that the force of friction is different for different substances while they are moving on the same inclined plane.

Activity -6:
Observing the magnetic force:

Question 6.
How do you prove that like poles repel and unlike poles attract each other? Which type of force is magnetic force? (Experimentation/Making hypothesis)
Answer:

• Take a sewing needle. Rub it with a bar magnet several times always moving the magnet in the same direction. After some time the needle acts like a magnet.
• With the help of a magnetic compass, you can identify the north and south poles of the needle.
• Pin a red-colored foam ball to the south pole and white ball to north pole of the needle; then drop it in a bowl of water it floats.
• Make another needle in the same way. Float both of them side by side facing the like ends.
• You observe they repel each other.
• Float them side by side facing the unlike ends. You observe they attract each other.
• From the above experiment, we conclude that Like poles repel and unlike poles attract each other.
• This action of pull or push results due to a magnetic force.
• Here magnet can attract or repel another magnet without any contact with the second magnet. So magnetic force is a non-contact force.

Activity – 7:
Observing electrostatic forces

Question 7.
Conduct an experiment/activity to observe the electrostatic forces? (Experimentation)
Answer:

• Take a balloon. Inflate it and tie tip the open end.
• Cut a paper into small pieces and place them on the
• balloon with a paper and bring the balloon near to pieces of paper.
• You observe paper pieces are attracted by the balloon.
• When the balloon is rubbed with a paper it acquires an electrostatic charge on its surface.
• The balloon is now said to be a charged body. When it is brought nearer to the pieces of paper. they acquire opposite charge and attracted b the balloon.
• The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.
• This force comes into play even when the bodies are not in contact. So electrostatic force is an example for the force at a distance.

Activity 8:
Visualizing magnetic field:

Question 8.
How do you visualize the magnetic field using a bar magnet and iron filings? (Experimentation)
Answer:

• Take a bar magnet and place it on a table, Place a thin white paper over it.
• Sprinkle the fine powder of iron (iron filings) on the paper. Tap the table or paper gently.
• You observe a pattern of iron filing around the bar magnet.
• Rotate the magnet in different directions and do the same. In every case pattern of iron filing around the bar magnet is formed.
• Iron filings set themselves in a pattern because they are affected by the magnetic force of the field created by thE bar magnet.
• Thus, the space around the magnet where its influence can be detected is called the ‘magnetic field’.

Activity- 9:
Effects of net force acting on a table:

Question 9.
Explain an activity to know the effect of different forces on net force acting on an object (Experimentation/Field investigation)
Answer:

• Take a heavy table which you can move only by pushing hard.
• Try to push it all by yourself. If the table do not move, then ask your friend to help in pushing it in the same direction. Now the table moves in the direction of force.
• Here net force acting on the table is equal to the sum of forces Since they act in the same direction.
• Now push the same table, but ask your friend to push it from the opposite side. The table doesn’t move if you both apply equal forces. Net force acting on the table is zero.
• When forces act on a body only in straight line are in s.me directions, the net force is the sum of all forces acting on the body. F_net = F₁ + F₂
• When forces act on a body in a straight liiw are in opposite directions, the net force is equal to difference between the two forces.
  F_net = F₁ + (- F₂) = F₁ – F₂.

Activity – 10;
Effects of stretched rubber bands on fingers:

Question 10.
Effects of stretched rubber bands on fingers. Show that the net force will act if there are more than one force is acting on the same object.
Answer:

1. Take a rubber band, stretch it using your fingers.
2. When you stretch the rubber band it exerts force on your fingers and you feel the force of pull on your finger.
3. Add another rubber hand around your fingers and stretch both together to the same length.
4. We feel by increase the number of rubber bands around our fingers and the force exert on our fingers is more.
5. Rubber band has F units and the force exerted by the second rubber band is F units. Then the net force of two rubber bands is F_net = F + F = 2F units

 

Activity – 11 :
Effect of force on change of the state of motion of an object and its direction.

Question 11.
Explain with an activity how the force affects the change of the state of motion of an object and its direction. (Experimentation)
Answer:

1. Place a football on the ground. The ball will remain there in the state of rest unless someone kicks the ball.
2. Kick the ball, it starts moving, kick the moving ball in the same direction, the speed of the bail increases.
3. Place your hand or leg against the ball, then the hail may be stopped or may be changed its direction of motion.
4. From this we conclude that the (orce changes the direction of motion and state of the body.

Activity-12:
Effects of net force on direction of moving object

Question 12.
Conduct an activity to show the effects of net force on direction of moving object.
Answer:

1. Hit a carom coin with the striker.
2. We can observe that in each case the direction of the coin changes.
3. We hit the coin with the striker not only the coin changes its direction, but also the strikes changes its direction too.
4. From this we can say that the net force stops a moving or makes a stationary object move and also changes the speed and direction of a moving object.

Activity – 13:
Effects of force on the shape of an object:

Question 13.
In the table given below, some situations are given. Complete the table and write your conclusion. – (Project work/Making hypothesis)
Answer:

From the above table we can understand that the force not only changes the state of motion of an object but also the shape of an object. It may change the shape temporarily or permanently, which is based on the nature of the object and the force applied on it.

Activity – 14 :
Chance in effect of force with area of contact:

Question 14.
How the effect of force changes with area of contact. (Experimentation/Field investigation)
Answer:
i. Take a pencil. Just push its rounded end on ‘our palm. There is less pain because less force acts on your palm.
ii. Now push from the other side of the pencil so that the sharp end is on your palm. Then you feel pain because more force is acting on your palm.
iii. From this you might have noticed that effect of force depends on area of contact on which the force is acting.
iv When there is a decrease in the area of contact of the force, then the effect of force increases and vice versa.

a) What is pressure? Write the units of pressure? (Conceptual understanding)
Answer:
The force acting on a unit area of a surface is called pressure.
Pressure- Force / Area.
SI. unit of pressure is Newton/meter² or N/m².
CCS unit of pressure is Dyne / cm².

Activity – 15:
Identifying effects of force:

Question 15.
How can you say that the contact area on which force is acting changes the effect of force? (Experimentation/Field investigation)
Answer:

• Take two trays and fill trays with lime powder.
• Take two rectangular bricks of equal mass and similar shape.
• Keep one brick vertically in one tray and the other brick horizontally in another tray.
• You may notice that the brick standing vertically sinks deeper in lime powder than the brick standing horizontally.
• Since the masses are same, the force applied on lime powder by them also same on both the trays.
• The difference lies in the surface area of the brick in contact with the lime powder, and this is responsible for the brick sinks in the lime powder.
• From the above we can see that for a given force if the surface area is smaller, the pressure will be greater.
• If we use larger area, we are spreading out the force, and the pressure becomes smaller.

Lab Activity

How do you find the Ìimiting force that can be borne by a string?
Answer:
Aim: To find the limiting force that can be borne by a string.
The material used: Spring balance, weights, light strings, weight hanger.
Procedure:

• A spring balance is suspend from rigid support.
• To it a weight hanger is connected.
• Slowly increase the weights in the weight hanger in steps of 50 grams and note the readings of spring balance.
• Repeat this experiment till the string breaks.
• Repeat the experiments with various strings and find out the limiting force of each wire.

a) What do you observe from the readings when it is pulled up and released to
move down?
Answer:
When it is pulled up the reading of spring balance increases that means apparent weight of the object increased.

b) Is the string broken when the whole system is pulled quickly up?
Answer:
If the whole system is pulled quickly up, the string may be broken.