EVENTS CONVENT HIGH SCHOOL
04/10/2021 CLASS-8 SESSION 2021-22
SUBJECT :SCIENCE
CHAPTER-3
SYNTHETIC FIBRES AND PLASTICS
______________________________________
Question 1.Explain why some fibres are called synthetic.
Answer:
Some fibres are called synthetic fibres because they are made by man using chemicals.
Question 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.
Question 3.Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called ____ or ____ fibres.
(b) Synthetic fibres are synthesised from a raw material called _____
(c) Like synthetic fibres, plastic is also a _____
Answer:
(a) man-made, artificial fibres
(b) petrochemicals
(c) polymer
Question 4.Give examples which indicate that nylon fibres are very strong.
Answer:
The following examples indicate that nylon fibres are very strong.
(i) They are used for making parachutes and ropes for rock climbing.
(ii) They are used in making seat-belts, fishing nets, tyre cord, a string for sports rackets and musical instruments.
Question 5.Explain why plastic containers are favoured for storing food.
Answer:
Plastic containers are favoured for storing food because of the following reasons:
(i) the plastics do not react with the food stored in them.
(ii) the plastics are lightweight and are strong.
(iii) they are easy to handle and safe.
Question 6.Explain the difference between thermoplastic and thermosetting plastics.
Answer:
| Thermoplastics | Thermosetting plastics |
| (i) These plastics softened on heating and can be bent easily. | (i) These plastics when moulded once, can’t be softened again. |
| (ii) They do not lose their plasticity. | (ii) They lose their plasticity. |
| (iii) Examples are polyethene, PVC, etc. | (iii) Examples are bakelite and melamine. |
Question 7.Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plugboards
Answer:
(a) Since, thermosetting plastics are a bad conductor of heat and do not get heated up while cooking, they are used for making saucepan handles.
(b) Since thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics, they are used for making electric plugs/switches/plugboards.
Question 8.Categorise the materials of the following products into ‘can be recycled’ and ‘can not be recycled’.
Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.
Answer:
| Can be recycled | Cannot be recycled |
| Plastic toys carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs. | Telephone instruments, cooker handles, ballpoint pens, electrical switches. |
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:
He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. In summers we have extensive sweating which is easily soaked by cotton shirts and hence, cotton clothes are much better than the clothes made from synthetic material.
Question 10.Give examples to show that plastics are non-corrosive in nature.
Answer:
The literal meaning of non-corrosive is resistant to get destroyed by chemical action.
Following are the examples that show that plastics are non-corrosive in nature.
- Plastic containers do not react with items stored in it.
- They do not get rusted when exposed to moisture and air.
- They do not decompose when left in open for a long period.
Question 11.Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.
Answer:
No, the handle and bristles of a toothbrush should not be made of the same material. This is because our gums are soft and the bristles should be made of soft material so that it does not harm the gums. On the other hand, the handles should be made up of hard material so that it can give a firm grip.
