Class 8 Science Assam || Chapter 17 - Synthetic Fibers And Plastics || Ncert || SEBA

NCERT Solutions – Class 8 Science
Chapter 3: Synthetic Fibres and Plastics

Exercise Questions

Class 8 · Science · Chapter 3

Q1. Explain why some fibres are called synthetic.

Solution:

They are called synthetic because they are made by humans in factories from chemicals, not taken directly from plants or animals.

Q2. 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.

Solution:

The correct option is (b) it is obtained from wood pulp.

Q3. Fill in the blanks with appropriate words.

(a) Synthetic fibres are also called __________ or __________ fibres.

(b) Synthetic fibres are synthesised from the raw material called __________.

(c) Like synthetic fibres, plastic is also a __________.

Solution:

(a) artificial, man-made

(b) petrochemicals

(c) polymer

Q4. Give examples which indicate that nylon fibres are very strong.

Solution:

• Parachutes and rock‑climbing ropes are made of nylon.
• Seat belts, fishing nets and tyre cords use nylon.
• Many sports rackets have nylon strings.

Q5. Explain why plastic containers are favoured for storing food.

Solution:

Plastic does not react with food, so food remains safe and its taste does not change easily in plastic containers.

Q6. Explain the difference between thermoplastic and thermosetting plastics.

Solution:

Thermoplastics	Thermosetting plastics
Can be bent easily.	Cannot be bent; may break on bending.
Soften on heating and can be reshaped.	Do not soften on heating and cannot be reshaped.

Q7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards

Solution:

(a) They do not get soft on heating and do not pass heat easily, so they are safe to hold.

(b) They do not conduct electricity and do not melt easily, so they are safe for electrical use.

Q8. Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.

Solution:

Can be recycled	Cannot be recycled
Plastic chairs	Cooker handles
Plastic bowls	Electrical switches
Plastic toys	Telephone instruments
Plastic covering on electrical wires
Carry bags
Ballpoint pens

Q9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.

Solution:

He should buy cotton shirts because cotton absorbs sweat and helps to keep the body cool.

Q10. Give examples to show that plastics are non-corrosive in nature.

Solution:

Strong cleaning liquids are stored in plastic bottles instead of metal ones because plastic does not rust or get damaged by chemicals.

Q11. Should the handle and bristles of a toothbrush be made of the same material? Explain your answer

Solution:

No. The handle should be hard and strong to hold, but the bristles should be soft and flexible to clean teeth gently.

Q12. ‘Avoid plastics as far as possible’. Comment on this advice.

Solution:

Plastics do not rot, so they stay in the environment and cause pollution.

When burnt they give poisonous gases, and plastic bags can choke animals if swallowed.

Q13. Match the terms of column A correctly with the phrases given in column B

A: (i) Polyester (ii) Teflon (iii) Rayon (iv) Nylon

B: (a) Prepared by using wood pulp (b) Used for making parachutes and stockings (c) Used to make non-stick cookware (d) Fabrics do not wrinkle easily

Solution:

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

Q14. ‘Manufacturing of synthetic fibres is actually helping conservation of forests’. Comment.

Solution:

Synthetic fibres reduce the use of plant‑based fibres, so fewer trees need to be cut.

This helps in saving forests.

Q15. Describe an activity to show that thermoplastic is a poor conductor of electricity

Solution:

Make a circuit with a battery, bulb and wires. Put a metal piece in the gap: the bulb glows.

Now put a plastic piece in place of metal: the bulb does not glow, showing plastic is a poor conductor of electricity.