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NCERT Solutions Science for Class 8 Chapter 3 SYNTHETIC FIBRES AND PLASTICS

class8 science Chapter 3

NCERT Solutions Science for Class 8 Chapter 3 SYNTHETIC FIBRES AND PLASTICS

science for class 8 Chapter 3 question answer

1. Explain why some fibres are called synthetic.
Answer : Some fibers are called synthetic because these types of fibers are made by man by joining small units. These small units are chemical substances. which join together to form polymers.

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.
Answer : (b) it is obtained from wood pulp.     (✓)

3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called natural 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.
Answer : Nylon fibre really so strong that we can make nylon parachutes and ropes for rock climbing.

5. Explain why plastic containers are favoured for storing food.
Answer : Plastic containers are used to store food, which has three main advantages.

• Plastic is nonreactive.
• Plastic is lightweight, strong and durable.
• Plastic is a poor conductors of heat.

6. Explain the difference between thermoplastic and thermosetting plastics.
Answer : the difference between thermoplastic and thermosetting plastics

Thermoplastic	Thermosetting plastics
Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics.	some plastics which when moulded once, can not be softened by heating. These are called thermosetting plastics.
Thermoplastic is a good conductor of heat.	Thermosetting plastics is a poor conductors of heat.
This plastic can be reused and recycled.	Its reuse and recycle is not possible.
Examples of thermosetting plastics – Plastics used in toys, combs and various types of containers.	Examples of thermosetting plastics are Bakelite and melamine. They are used in electrical switches, handles of various utensils, etc.

7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer :
(i) Why the saucepan handle is made of thermosetting plastics?
Thermosetting plastic is a poor conductor of heat. Along with this, it does not melt on fire. Due to which it is used in making the hands of Dekchi.

(i) Why the Electric plugs/switches/plug boards are made of thermosetting plastics?
Thermosetting plastic is a poor conductor of electricity. Thus there is no risk of electric shock. Along with this, it does not melt on fire. Due to which it is used in making electrical plug/switch/plug board.

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.
Answer –

Can be recycled	Cannot be recycled
Telephone instruments, cooker handles, plastic bowls, plastic chairs, electrical switches	Plastic toys, carry bags, ball point pens, plastic covering on electrical wires, plastic chairs

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 – We would recommend Rana to buy cotton shirts during summers. Because sweat comes less in cotton clothes and absorbs sweat. Cotton shirts dry quickly. It doesn’t get hot quickly. Does not stick on the body.

10. Give examples to show that plastics are noncorrosive in nature.
Answer – When metals like iron are exposed to moisture and air, they rust. But plastics do not react with water and air. They do not corrosion easily. Therefore, they are non-corrosive in nature, so they are used to store various types of substances, including many chemicals.

11. Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer – No, the brush handle and the bristles should not be made of the same material. The handle of the brush should be of strong material so that it can be used well. On the contrary, the bristles should be of soft, soft material so that there is no damage to the teeth and gums in the mouth.

12. ‘Avoid plastics as far as possible’. Comment on this advice.
Answer : Plastic is a biodegradable material. Which is not easily decomposed by natural processes. Naturally, plastic takes many years to decompose, it is not eco-friendly. It causes environmental pollution. In addition, when a material made of plastic is burnt, it takes a long time to burn completely. This process pollutes the environment by emitting a large amount of toxic fumes. Therefore, we should avoid the use of plastic as far as possible and use bags made of cotton or jute.

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

Answer :

	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.
Answer – Synthetic fibers are manufactured by chemicals in factories. For which there is no need to cut forests and kill animals. Which helps in the conservation of forests.

15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer – Plastics that can be easily broken are called thermoplastics. Such as – PVC and polythene.
activity : By connecting wires to the positive and negative parts of a cell, connecting a bulb and a thermoplastic object to it, the bulb does not light up. But when the thermoplastic object is removed from this activity, the bulb burns out. From this it can be concluded that thermoplastic is a poor conductor of electricity and does not allow electricity to be affected from inside.