AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

AP State Board new syllabus 8th Class Physics Guide 10th Lesson Combustion and Flame Textbook Exercise Questions and Answers.

AP 8th Class Physical Science 10th Lesson Questions and Answers Combustion and Flame

8th Class Physics 10th Lesson Combustion and Flame Questions and Answers (Exercise)

Question 1.
List conditions under which combustion can take place.
Answer:

  • Combustion takes place in the presence of air (oxygen) only.
  • Combustion takes place when the fuel reaches its ignition temperature only.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 2.
Fill in the blanks.

a) Burning of wood and coal causes of ………… air.
Answer: pollution

b) A liquid fuel, used in homes is …………
Answer: kerosene

c) Fuel must be heated to its ………… before it starts burning.
Answer: ignition temperature

d) Fire produced by oil cannot be controlled by …………
Answer: water

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 3.
Explain how the use of CNG in automobiles has reduced pollution in our cities.
Answer:

  • CNG (Compressed Natural Gas), is a cleaner fuel.
  • It produces the harmful produces in very small amounts.
  • Now day the use of diesel and petrol as fuels in automobiles is being replaced by CNG.
  • So, it has been reducing pollution in our cities.

Question 4.
Compare LPG and wood as fuels.
Answer:

LPG Wood
1. It is gaseous fuel. 1. It is solid fuel.
2. It has high calorific value. 2. It has low calorific value.
3. It produces the harmful produces 3. It produces the harmful produces in
in very small amounts. very high amounts.
4. It can be stored in cylinders. 4. It can’t be stored in cylinders.
5. It can send easily anywhere through the pipe lines. 5. It cannot send easily anywhere through the pipe lines.
6. It doesn’t cause deforestation. 6. It causes deforestation.
7. Its ignition temperature is low’ 7. Its ignition temperature is high.
8. Combustion starts quickly. 8. Combustion starts slowly.

Question 5.
Give reasons.
a) Water is not used to control fires involving electrical equipment.
b) LPG is a better domestic fuel than wood.
c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
Answer:
a) If electrical equipment is on fire, water may conduct electricity and causes electrical shock to those trying to do use to control the fire. Water is not used to control fires involving electrical equipment.

b) LPG is a less pollutant and it does not release smoke. But, burning of wood releases smoke and causes ill health to households. LPG has low ignition temperature and catches fire easily. But wood takes much heat to start combustion. LPG in cylinder requires less area to store. But wood requires more area. So, LPG is a better domestic fuel than wood.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

c) When we heat the piece of paper which is wrapped around an aluminium pipe, the given heat transfers to the aluminium. Hence the ignition temperature of the piece of paper does not rise quickly. So, the piece of paper does not catch fire.

Question 6.
Make a labelled diagram of a candle flame.
(OR)
Draw the diagram that shows different zones of candle flame.
Answer:
AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame 3

Question 7.
Name the unit in which the calorific value of a fuel is expressed.
Answer:
The calorific value of a fuel is expressed in a unit called kilojoule per kg (kJ/kg).

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 8.
Explain how CO2 is able to control fires.
Answer:

  •  CO2, being heavier than oxygen, covers the fire.
  • Since the contact between the fuel and oxygen is cut off, the fire is controlled.
  • When released from the cylinder, CO2 expands enormously in volume and cools down.
  • So, it not only forms a blanket around the fire, it also brings down the temperature of the fuel.

Question 9.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.
Answer:

  • The heap of green leaves contains water.
  • So, it requires more heat to get the ignition temperature.
  • Whereas dry leaves do not contain water and catch fire quickly.

Question 10.
Which zone of a flame does a goldsmith use for melting gold and silver and why?
Answer:
Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver, because the outerinost zone is a very hot portion than inner or middle portions of the flame.

Question 11.
In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.
Answer:
Calorific value = kilo joule per kg .
4.5 kg of a fuel gives 180,000 kJ
1 kg of the fuel gives = ?
= 180000/4.5
= 40000 kJ/kg
∴ The calorific value of the fuel =40000 kJ/kg

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 12.
Can the process of rusting be called combustion? Discuss.
Answer:

  • Combustion takes place when a fuel catches fire in the presence of oxygen at a particular temperature.
  • Rusting of iron is not combustion, because iron is not a fuel and it does not catch fire in the presence of air.

(Note: The process of rusting of iron is oxidation, but not combustion)

Question 13.
Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer:
Ramesh water will get heated in a shorter time because the outermost part of the flame is a very hotter part than the yellow part of the candle flame.

Extended Learning – Activities and Projects

Question 1.
Survey the availability of various fuels in your locality. Find out their cost per kg and prepare a tabular chart showing how many kJ of various fuels you can get for every rupee.
Answer:

S.No. TYPE OF FUEL COST PER LITRE/KG Calorific value Per kg (approx.)kJ COST PER KJ Rs.
1. LPG 72/- 55 Rs.1.30
2. Petrol 110/- 45 Rs.2
3. Deisel 98/- 45 Rs.2.17
4. Kerosene 60/- 45 „ Rs.1.33
5. Wood 10/- 20 Rs.0.50
6. Coal 50/- 30 Rs.1.66

Question 2.
Find out the number, type and location of fire extinguishers available in your school, nearby shops and factories. Write a brief report about the preparedness of these establishments to fight fire.
Answer:

S.No. Location No. of fire Extinguisher Type
1) School 1 CO2
2) Factory 10 CO2, DCP
3) Cinema hall 8 CO2, DCP
4) Shopping mall 9 CO2, DCP

Preparedness :

  • Staff of various organizations has been given proper training in firefighting.
  • Fire extinguishers are ready to use.
  • Wind directions balloons are also fixed at the top of the buildings.
  • Special fire exits Routes are marked.
  • Alarms are also fixed.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 3.
Survey 100 houses in your area. Find the percentage of households using LPG, Kerosene, wood and cattle dung as fuel.
Answer:
Do it yourself.
Survey form :

S.No. Name of the house-hold LPG/kerosene/wood/cattle dung as fuel

Percentage of

  • LPG : …………….
  • Wood : …………….
  • Cattle dung : …………….
  • Kerosene : …………….

Question 4.
Talk to people who use LPG at home. Find out what precautions they take in using LPG.
Answer:
Precautions taken by the people who use LPG at home :

  • Off the regulator after usage of gas every time.
  • Check the pipe regularly for leakages.
  • Use branded pipes only.
  • Use a lighter to ignite.
  • Don’t keep flammable substances near the stove.
  • Clean burners regularly.
  • Don’t leave the flame without cooking.
  • Use pressure cookers.
  • Don’t place the stove under the gas cylinder.
  • If any leakage is found open the windows and doors. But don’t switch off or on the electrical appliances.
  • Don’t pour the hot water on the cylinder.
  • Don’t put the cylinder horizontally.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Question 5.
Make a model of a fire extinguisher. Place a short candle and a slightly taller candle in a small dish filled with baking soda. Place the dish at the bottom of a large bowl. Light both the candles. Then pour vinegar into the dish of baking soda. Take care. Do not pour vinegar on the candles. Observe the foaming reaction. What happens to the candles? Why? In what order?
Answer:
Observations :

  • The short candle puts off first.
  • Then the taller candle puts off next.

Reason :
When baking soda is reacted with vinegar
it releases carbon dioxide gas in the bowl. CO2 goes up slowly from the bottom and reaches the shorter candle first. So, the shorter candle puts off first.
AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame 4

8th Class PS 10th Lesson Questions and Answers (Lab Activities)

Activity – 1

Question 1.
How do you classify the materials like straw, matchsticks, kerosene oil, paper, iron nails, stone pieces, glass etc., into combustible and non-combustible?
Answer:

  • Collect some materials like straw, matchsticks, kerosene oil, paper, iron nails, stone pieces, glass etc.
  • Under the supervision of your teacher try to burn each of these materials one by one.
  • If combustion takes place mark the material combustible, otherwise mark it noncombustible.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Combustible and Non-combustible Substances

Material Combustible Non-combustible
Wood
Paper
Iron nails
Kerosene oil
Stone piece
Straw
Charcoal
Matchsticks
Glass

Activity – 2

How do you prove that air is necessary for combustion?
Answer:
Procedure :

  • Fix a lighted candle on a table.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame 5

Case-a :

  • Put a glass chimney over the candle and rest it on a few wooden blocks in such a way that air can enter the chimney.
  • Observe what happens to the flame.

Case – b :

  • Now remove the blocks and let the chimney rest on the table.
  • Again, observe the flame.

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Case – c:

  • Finally, put a glass plate over the chimney.
    Watch the flame again.

Observations :

  • The candle burns freely in case (a) when air can enter the chimney from below.
  • In case (b), when air does not enter the chimney from below, the flame flickers and produces smoke.
  • In case (c), the flame finally goes off because the air is not available.

Conclusion :
We find that air is necessary for combustion.

Question 3.
How do you prove that the burning of charcoal takes place in the presence of air only ?
Answer:

  • Place a piece of burning wood or charcoal on an iron plate or Tawa.
  • Cover it with a glass jar or a tumbler, or a transparent plastic jar.
  • Observe what happens.
  • Charcoal stop burning after sometime due to lack of air.

Conclusion : The burning of charcoal takes place in the presence of air only.

Activity – 4

How do you demonstrate the concept of ignition temperature with an activity?
Answer:

  • Make two paper cups by folding a sheet of paper.
  • Pour about 50 mL of water in one of the cups.
  • Heat both the cups separately with a candle.
  • The empty paper cup burns quickly.
  • The paper cup with water does not burn but heats up.
  • If we continue heating the cup, we can even boil water in the paper cup.
  • The heat supplied to the paper cup is transferred to water by conduction.
  • So, in the presence of water, the ignition temperature of paper is not reached.
  • Hence, it does not burn.

Activity – 5.

Recall your experience of burning a magnesium ribbon in Class VII. If you do not have experience of burning the remaining Items in table, you can do that now. Record your observations and mention whether on burning the material forms a flame or not.
Materials forming Flame on Burning

S.No. Material Forms flame Does not form flame
1. Candle
2. Magnesium
3. Camphor
4. Kerosene Stove
5. Charcoal

Answer:

S.No. Material Forms flame Does not form flame
1. Candle yes no
2. Magnesium yes no
3. Camphor yes no
4. Kerosene Stove yes no
5. Charcoal no yes

AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame

Activity – 5

Question 6.
How do you prove that the substances which vapourize during burning, give flames?
Answer:
AP 8th Class Physics 10th Lesson Questions and Answers Combustion and Flame 6

  • Light a candle.
  • Hold a 4-5cm long thin glass tube with a pair of tongs and introduce its one end in the dark zone of a non-flickering candle flame.
  • Bring a lighted matchstick near the other end of the glass tube.
  • You can see a flame caught at this end of the glass tube after a while.
  • Notice that the wax near the heated wick melts quickly.
  • The vapours of wax coming out of the glass tube be the cause of the flame produced.
  • We can say that the substances which vapourise during burning, give flames.

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