AP 8th Class Physics 4th Lesson Questions and Answers Synthetic Fibres and Plastics

AP State Board new syllabus 8th Class Physics Guide 4th Lesson Synthetic Fibres and Plastics Textbook Exercise Questions and Answers.

AP 8th Class Physical Science 4th Lesson Questions and Answers Synthetic Fibres and Plastics

8th Class Physics 4th Lesson Synthetic Fibres and Plastics Questions and Answers (Exercise)

Question 1.
Explain why some fibres are called synthetic.
Answer:
Some fibres are called synthetic because they do not occur in the nature. Generally, they are obtained by chemical processing of petrochemicals, e.g. nylon, polyester, acrylic etc.

Question 2.
Rayon is different from synthetic fibres because
(a) it has a silk-like appearance.
(b) it is obtained from wood pulp.
(c) its fibres can also be woven like those of natural fibres.
Answer:
Rayon is obtained from wood pulp.

Question 3.
Fill in the blanks with appropriate words.
a) Synthetic fibres are also called ………….. or ………….. fibres.
b) Synthetic fibres are synthesised from raw material called ……………
c) Like synthetic fibres, plastic is also a ……………
Answer:
a) man-made, artificial
b) petrochemicals
c) polymer

Question 4.
Give examples which indicate that nylon fibres are very strong.
Answer:
Nylon fibres are very strong. Thus, they are used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.

Question 5.
Explain why plastic containers are favoured for storing food.
Answer:
Advantages of storing foods in plastic containers are as follows:

• Plastics do not react with food items,
• Plastics are strong, light and durable
• Plastics do not get rusted,
• Plastic containers are airtight
• They are easy to handle

Question 6.
Explain the difference between thermoplastic and thermosetting plastics.
Answer:
Difference between thermoplastics and thermosetting plastics are as follows.

Thermoplastics	Thermosetting plastics
1) There are the plastics, which get deformed easily on heating. E.g: Polythene and PVC.	1) These are plastics, which when moulded once, cannot be softened by heating. E.g: Bakelite and melamine.
2) These are used for making toys, combs, various types of containers, etc.	2) In thermosetting plastics, bakelites are used for making electrical switches, handle of various utensils etc.  Melamaine are used for making floor tiles, kitchenwares and fabrics which resist fire.

Question 7.
Explain why the following are made of thermosetting plastics.
a) Saucepan handles,
b) Electric plugs/switches / plug boards
Answer:
a) Saucepan handles are made of thermosetting plastics because it is a bad conductor of heat and do not get heated up while cooking.
b) Electric plugs/switches / plug boards are made of thermosetting plastics because it is bad conductor of electricity.

Question 8.
Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled.’
Telephone instruments, plastic toys, cooker handles, carry bags, ball point pens, plastic bowls, plastic covering on eletrical wires, plastic chairs, electrical switches.
Answer:
Materials are categorised below:

Can be recycled	Cannot be recycled
i) Plastic toys ii) Carry bags iii) Plastic bowls iv) Ball point pens v) Plastic chairs vi) Electric wires with plastic covering	i) Cooker handles ii) Electric switches iii) Telephone instruments

Question 9.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer:
The absorbing capacity of synthetic fibres is less than cotton fibres, so the synthetic fabric soaks less water than cotton fabric. In summers we have extensive sweating which must be soaked up by our clothings. Since synthetic fabric is poor in this property we prefer clothes in summer.

Question 10.
‘Give examples to show that plastics are noncorrosive in nature.
Answer:
Examples given below shows that plastics are non-corrosive in nature.

• They do not react with the chemical or other items stored in the containers of it.
• They do not decompose when left in open for a long period.
• They do not react with any substances. That is why, they are used to store various kinds of materials.
• Plastics do not react with air and water, so it will not show corrosion.

Question 11.
Should the handle and bristles of a toothbrush be made of the same material? Explain you answer.
Answer:
No, handle and bristles of a toothbrush should not be made of the same material because the handle should be hard while bristles should be made of the soft materials. Bristles should be soft so that it does not harm the gum of teeth. Handle should be made of hard material so that it gives the firm grip.

Question 12.
‘Avoid plastics as far as possible’. Comment on this advice.
Answer:
We should avoid plastics as far as possible because plastics are non-biodegradable materials. Plastics take several years to decompose this cause environmental pollutions. Burning of plastics releases poisonous gases into the atmosphere causing air pollution.

Question 13.
Match the terms of column A correctly with the phrases given in column B.

(i) Polyester	(a) Prepared by using wood pulp
(ii) Teflon	(b) Used for making parachutes and stockings
(iii) Rayon	(c) Used to make non-stick cookwares
(iv) Nylon	(d) Fabrics do not wrinkle easily

Answer:

Question 15.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
Activity is given below that shows that thermoplastic is a poor conductor of electricity. Activity: Take two wires. One wire is kept naked and another wire has plastic covering. Make two circuits, one with naked wire and another with plastic covering. We will feel shock with naked wire while plastic covered wire will not give any shock.

Extended Learning – Activities and Projects

Question 1.
Have you heard of the campaign : “Say No To Plastics”. Coin a few more slogans of this kind. There are certain governmental and non-governmental organisations who educate the general public on how to make wise use of plastics and develop environment friendly habits. Find out organisations in your area which are carrying out awareness programmes. If there is none, form one.
Answer:
Yes. Few such slogans may be – ‘Use Jute bags’, ‘Re-use plastics’. Conserve India, Jana Vignana Vedika, Vigyan Bharthi’ are some NGOs educating the general public on how to make wise use of plastics.

Question 2.
Organise a debate in the school, Children may be given an option to role play as manufacturers of synthetic fabrics or those of fabrics from natural soures. They can then debate on the topic ‘My Fabric is Superior’.
Answer:
My Fabric is Superior
A fibre is a kind of thread which is strong and flexible. All fabrics are made from either natural fibres or artificial fibres. Those fibres which are obtained from natural sources are called natural fibres.

While a synthetic fibre is made up of a long chain of small units joined together to form a polymer. We already have natural fibres to make clothes, bags, curtains. No doubt, natural fibres are beautiful and comfortable but they are not very much durable. The clothes made of synthetic fibres are attractive as well as durable. Synthetic fibres are cheaper than the clothes made of natural fibres.

A lot of dresses made up of synthetic fibres have become very popular because of the following reasons.

• Chemical resistance
• Resistant to weather,
• Light weight
• Strong and durable
• Toughness
• Insulation

Another advantage of synthetic fibres is that we can make fabrics having desired properties. Synthetic fibres are used in making parachutes, mattresses, umbrella etc. So we can say that synthetic fibres are superior to natural fibres for us.

Question 3.
Visit five families in your neighbourhood and enquire about the kind of clothes they use, the reason for their choice and advantages of using them in terms of cost, durability and maintenance. Make a short report and submit it to your teacher.
Answer:
Activity for home.

Question 4.
Devise an activity to show that organic waste is biodegradable while plastic is not.
Answer:
Take some waste materials of both types. Dig two small pits of about metre deep. Put these wastes in the pits. We see that organic waste has either been degraded or started degrading while the plastic waste has not started degrading.

8th Class PS 4th Lesson Questions and Answers (Lab Activities)

Activity – 1

To compare the tensils strength of different fibers of the same thickness and the same length.
Answer:
Method :

• Take an iron stand with a clamp. Take a cotton thread of about 60 cm length.
• Tie it to the clamp so that it hangs freely from it as shown in Fig.
• At the free end suspend a pan so that weight can be placed in it.
• Add weight one by one till the thread breaks (In place of weights you may use marbles)
• Note down the total weight required to breake the thread. This weight indicates the strength of the fibre.
• Repeat the same activity with threads of wool, polyestert silk and nylon.
• Tabulate the data as shown in table. Arrange the threads in order of their increasing strength.

S.No.	Type of Thread/Fibre	Total weight required to break the thread
1.	Cotton	12gm
2.	Wool	70 gm
3.	1 Silk	50 gm
4.	Nylon	100gm

Observation : You observe that nylon thread holds maximum number of marbles before it breakes, followed silk, cotton and wool (least strong). The thread which holds the maximum number of weights is the strongest.
Precaution : All threads should be of the same length and almost the same thickness.
Conclusion: Tensile strength of nylon (Synthetic fibre) is more than that of silk, cotton and wool.

Activity – 2

To observe and compare the amount of water absorbed by natural and synthetic fibres.
Answer:
Method: Take two cloth pieces of the same size roughly half a metre square each. One of these should be from natural fibre. The other could be a synthetic fibre.

Soak the pieces in different mugs each containing the same amount of water. Take the pieces out of the containers after five minutes and spread them in the sun for a few minutes. Observe the amount of water left in each mug and the fabric that dries up faster.

Observation : You will observe that the mug in which the natural fabric was dipped will have less water as compared to the mug in which the synthetic fabric was dipped. The synthetic fabric will dry faster as compared to the natural fabric as it absorbs, less water.

Conclusion : Natural fibres absorbs more water as compared to artificial fibres.