Class 8 - Science
Chapter 3 - Synthetic Fibres and Plastics
Top Block 1
Question :1. Explain why some fibres are called synthetic.
Answer :
Since man-made fibres are obtained by the synthesis of petrochemicals, they are called synthetic fibres.
Question :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.
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 synthesized from raw material called ———–.
(c) Like synthetic fibres, plastic is also a —————-.
Answer :
Fill in the blanks with appropriate words.
(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.
Question :4. Give examples which indicate that nylon fibres are very strong.
Answer :
They are used to make parachutes and ropes for rock climbing.
Question :5. Explain why plastic containers are flavored for storing food.
Answer :
The main advantage of using plastic for storing food are-
a. Plastic has light weight.
b. Good strength.
c. Easy to handle.
Question :6. Explain the difference between thermoplastic and thermosetting plastics.
Answer :
| Thermoplastic | Thermosetting plastics |
|---|---|
| 1. These are the plastics which get deformed easily on heating and can be easily bent. | 1. These are the plastics which when molded once cannot be softened by heating. |
| 2. These are used for making toys, combs and various types of containers. | 2. Used for making electrical switches and handles of various utensils. |
| 3. Ex- polythene, PVC. | 3. Ex- Bakelite, melamine etc |
Mddle block 1
Question :7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plug/ switches /plug boards
Answer :
(a) Saucepan handles: Saucepan handles are made from the thermosetting plastics because these are bad conductors of heat and electricity. They do not bend or deform on heating.
(b) Electric
