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SEBA Class 8 Science Chapter 17 Synthetic Fibres And Plastics
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Synthetic Fibres And Plastics
Chapter: 17
PART – II
EXERCISE
1. Explain why some fibres are called synthetic.
Ans: Synthetic fibres are called so because they are man-made and produced through chemical processes, usually from raw materials like petroleum. These fibres are not naturally occurring and are designed to mimic or improve upon the properties of natural fibres like cotton, silk, or wool.
2. Mark (✓) the correct answer.
(i) 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.
Ans: (b) It is obtained from wood pulp.
3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called _______ or ________ fibres.
Ans: Man-made or artificial.
(b) Synthetic fibres are synthesised from raw material called_________.
Ans: Petroleum.
(c) Like synthetic fibres, plastic is also a__________.
Ans: Polymer.
4. Give examples which indicate that nylon fibres are very strong.
Ans: Nylon fibres are used for making parachutes and ropes for rock climbing. These examples indicate that nylon fibres are very strong. Moreover, Nylon fibre is actually stronger than steel wire.
5. Explain why plastic containers are favoured for storing food.
Ans: Plastic containers are preferred for food storage because they are non-reactive and would not react with the food’s ingredients.
6. Explain the difference between thermoplastic and thermosetting plastics.
Ans: (a) Saucepan handles: Thermosetting plastics are used for saucepan handles because they are heat-resistant and will not deform under high temperatures.
(b) Electric plugs/switches/plug boards: These are made of thermosetting plastics to ensure they do not melt or catch fire due to electrical current and heat.
7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles.
Ans: Thermosetting plastics are used for saucepan handles because they are heat-resistant and will not deform under high temperatures.
(b) Electric plugs/switches/plug boards.
Ans: Electric plugs/ switches/ plug boards are saucepan is made of thermosetting plastic because it is a bad conductor of electricity.
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, electrical switches.
Ans:
| Can be recycled: | Cannot be recycled: |
| Telephone instruments | cooker handles |
| Plastic toys | ball point pens |
| carry bags | |
| ball point pens | |
| plastic chairs | |
| electrical switches. | |
| plastic covering on electrical wires |
9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Ans: Rana should buy cotton shirts. It is because cotton is a bad conductor of heat. It does not allow the outer heat to enter in our body and thus protects our body from heat. It also has more capacity to hold moisture than the synthetic clothes. Synthetic fibres tend to trap heat and moisture, making them less comfortable in summer.
10. Give examples to show that plastics are noncorrosive in nature.
Ans:Plastics are non-corrosive in nature, they do not react even if they come in contact with strong chemicals. For example, plastic pipes used in plumbing systems do not corrode like metal pipes.
11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Ans: No, the handle and bristles of a toothbrush should be made of different materials. The handle of a toothbrush should be hard and strong, so it should be made from plastic. while the bristles should be made of nylon (flexible and soft) to effectively clean teeth without causing harm.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Ans: While plastics are useful in many applications, but plastics add to the environmental pollution. They cannot be burnt as when burnt, they release poisonous gases. Plastic bags thrown in the garbage dump are swallowed by animals like cows. These plastic bags choke their respiratory system and can even prove fatal.
13. Match the terms of column A correctly with the phrases given in column B.
| A | 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. |
Ans:
| A | B |
| (i) Polyester. | (d) Fabrics do not wrinkle easily. |
| (ii) Teflon. | (c) Used to make non-stick cookwares. |
| (iii) Rayon. | (a) Prepared by using wood pulp. |
| (iv) Nylon. | (b) Used for making parachutes and stockings. |
14. ‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Ans: If we use synthetic fibres, we do not require to cut trees down and hence helps in conservation of forest. Since synthetic fibres are obtained from petrochemicals, they have very well substituted the use of natural fibres like cotton, silk, wool and jute which are obtained from plants and animals.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Ans: Activity:
(i) Take a simple electric circuit containing a battery, a bulb, and connecting wires.
(ii) Cut a small piece of thermoplastic material (like a piece from a plastic ruler or bottle cap).
(iii) Connect it between the wires in place of a conductor and complete the circuit.
Observation: The bulb does not glow, showing that electricity does not pass through the thermoplastic.
Conclusion: Thermoplastics are poor conductors of electricity because they do not allow electric current to pass through them.
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