Synthetic Fibres and Plastics - Solutions

CBSE Class–VIII Science
1. Explain why some fibres are called synthetic.
Since man-made fibres are obtained by the synthesis of petrochemicals, so they are called synthetic fibres.

2. Mark ( ✓ ) the correct answers :
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.
(b) Synthetic fibres are synthesized from raw material called __________ .
(c) Like synthetic fibres, plastic is also a ___________ .
Ans: (a) Synthetic fibres are also called artificial or man-made fibres.
(b) Synthetic fibres are synthesized from raw material called polymer.
(c) Like synthetic fibres, plastic is also a petrochemicals.

4. Give examples which indicate that nylon fibres are very strong.
They are used to make parachutes and ropes for rock climbing.

5. Explain why plastic containers are favored for storing food.
Ans: The main advantages of using plastic for storing food are -
a. Plastic has light weight.
b. Good strength.
c. Easy to handle.

6. Explain the difference between thermoplastic and thermosetting plastics.
Thermosetting plastics
(i) These are the plastics which become soft on heating; they can be melted repeatedly by heating.
(ii) These are used for making toys, combs and various types of containers.
(iii) Ex- polythene, PVC, polystyrene, etc.
(i) These are the plastics which do not become soft on being exposed to moderately high temperatures.
(ii) Used for making electrical switches and handles of various utensils.
(iii) Ex- Bakelite, melamine etc.

7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plug/ switches /plug boards
Ans: (a) Saucepan Handles: Saucepan handles are made from the thermosetting plastics because these are bad conductors of heat. They do not bend or deform on heating.
(b) Electric plug/Switches/Plug BoardsElectric plug/switches/plug boards are made from thermosetting plastics because thermosetting plastics are bad conductor of heat and electricity also. Hence it is used to make such articles.