NCERT Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics are prepared by subject professionals and it includes the solution to all the questions present in the NCERT class 8 Science textbook. All the NCERT solutions are framed in a systematic manner according to the latest CBSE class 8 science syllabus (2020-21). All the solutions present in this study material includes detailed explanations, more examples, formulas, tips and tricks, Important questions.
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NCERT Solutions for Class 8 Science Chapter 3 : Fibres and Plastics
1. Explain why some fibres are called synthetic.
Some fibres are called as synthetic fibres because they are man-made fibres prepared by using chemicals. Nylon, rayon, acrylic, polyester etc. are some of the examples of synthetic fibre.
2. Mark ( ) the correct answer.
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.
Option (b) is the correct answer.
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 __________ .
(a) Synthetic fibres are also called artificial or man-made fibres.
(b) Synthetic fibres are synthesised from raw material called petrochemicals.
(c) Like synthetic fibres, plastic is also a polymer.
4. Give examples which indicate that nylon fibres are very strong.
Examples which indicate that nylon fibres are very strong are:
They are used for making parachutes and ropes for rock climbing.
They are used in making seat-belts, shiny nets, tyre cord, a string for sports rackets and musical instruments.
5. Explain why plastic containers are favoured for storing food.
Plastic containers are favoured for storing food because of the following reasons:
(i) Plastic does not react with the food stored in them.
(ii) Plastic is lightweight and very strong.
(iii) Plastic is easy to handle and safe.
6. Explain the difference between thermoplastic and thermosetting plastics.
These plastics softened on heating and can be bent easily. They do not lose their plasticity. Examples: polythene, PVC, etc.
Thermosetting plastics These plastics when moulded once can’t
be softened again.
They lose their plasticity.
Examples: melamine, bakelite, etc.
7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
(a) Thermosetting plastics are bad conductors of heat and so they do not get heated up while cooking. That is why thermo setting plastics are used for making saucepan handles.
(b) Thermosetting plastics are bad conductors of electricity and thus electric current does not pass through them. This is the reason why thermosetting plastics are used for making electric plugs/switches/plug boards.
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 electrical wires, plastic chairs and
Can be recycled
Plastic toys carry bags, plastic bowls,
plastic covering on electrical wires, plastic
Cannot be recycled
Telephone instruments, cooker handles,
ballpoint pens, electrical switches
9. Rana wants to buy shirts for summer. Should he buy cotton shirts or
shirts made from synthetic material? Advise Rana, giving your reason.
Rana should buy cotton shirts. This is because cotton can hold more moisture than the synthetic clothes. In summers cotton shirts can easily soak the sweat and hence, cotton clothes are much better than the clothes made from synthetic material.
10. Give examples to show that plastics are noncorrosive in nature.
Examples to show that plastics are noncorrosive in nature are:
They do not rust when exposed to moisture or air.
They do not decompose if left in open for a long period.
11. Should the handle and bristles of a tooth brush be made of the same
material? Explain your answer.
No, the handle and bristles of a toothbrush should not be made of the same material. The bristles should be made of the soft material because our gums are soft and they should not be harmed. On the other hand, the handles should be made up of hard material so that it can give a firm grip.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Plastics must be avoided as far as possible. Plastics are made up of non-biodegradable materials. When the plastic is burnt, a lot of poisonous fumes are released into the atmosphere which causes air pollution. The plastic materials when eaten up by the animals (like cows), choke their respiratory system causing the death of the animal. The waste plastic articles thrown carelessly might get into drains and sewers, and block them. In a nutshell, plastics can be considered a threat to our environment.
13. Match the terms of column A correctly with the phrases given in
(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 cookware
(iv) Nylon (d)Fabrics do not wrinkle easily
Polyester Fabrics do not wrinkle easily
Teflon Used to make non-stick cookware’s
Rayon Prepared by using wood pulp
Nylon Used for making parachutes stockings
14 ‘Manufacturing synthetic fibres is actually helping conservation of
The manufacturing of synthetic fibres is helpful in the conservation of forests. This is because if we use natural fibres, the raw materials for them have to be derived from the plants, which require cutting off lots of trees. Thus, manufacturing synthetic fibres proves to be helpful in the conservation of forests.
15. Describe an activity to show that thermoplastic is a poor conductor of
We design a circuit in order to show that thermoplastic is a poor conductor of electricity.
We need a bulb, some wires, a battery, a piece of metal and a plastic pipe (as shown in the figure below).
After setting the circuit, switch on the current. It will be observe that the bulb glows in the former case. In the latter case, the bulb does not glow.
Hence a plastic pipe (which is a thermoplastic) is shown to be a poor conductor of electricity.