Question: What are synthetic fibres or artificial fibres? Give the types of synthetic fibres with examples.
Answer: Synthetic fibres are man-made fibres prepared from chemicals, mainly petrochemicals, instead of natural sources. They are also called artificial fibres.
The main types are:
(i) Rayon – made from wood pulp
(ii) Nylon – strong and elastic fibre
(iii) Polyester – used in clothes like Terylene
(iv) Acrylic – used as a substitute for wool.
Question: What are Natural fibres ? Give the types of Natural fibres with examples.
Answer: Natural fibres are fibres obtained from plants or animals. They are not man-made.
Types of natural fibres:
(i) Plant fibres – e.g., cotton and jute
(ii) Animal fibres – e.g., wool and silk
Question: Write the characteristics of synthetic fibres.
Answer: The Characteristics of synthetic fibres are:
(i) They are strong and durable.
(ii) They are light in weight and easy to handle.
(iii) They are elastic and do not wrinkle easily.
(iv) They are less absorbent and dry quickly.
(v) They are resistant to chemicals and moths.
(vi) They are usually cheaper than natural fibres.
Question: Write the differences between synthetic fibres and natural fibres.
Answer: The Differences between Synthetic Fibres and Natural Fibres are:
|
Synthetic Fibres |
Natural Fibres |
|
Made by humans using chemicals. |
Obtained from plants and animals. |
|
Examples: nylon, polyester, acrylic. |
Examples: cotton, wool, silk. |
|
Strong and durable. |
Less strong compared to synthetic fibres. |
|
Do not decompose easily. |
Biodegradable in nature. |
|
Can melt on heating. |
Do not melt, may burn instead. |
Question: What is a polymer ?
Answer: A polymer is a large molecule formed by joining many small repeating units called monomers. These units link together to form long chains. Polymers can be natural, like rubber, or synthetic, like plastic.
Question: What are petrochemicals ?
Answer: Petrochemicals are useful chemical substances obtained from petroleum and natural gas. They are used to make products like plastics, synthetic fibres, detergents, and medicines. These materials are widely used in our daily life.
Question: What is a biodegradable material? Give one example.
Answer: A biodegradable material is a substance that gets decomposed naturally by microorganisms like bacteria. These materials do not harm the environment much.
Example: vegetable waste or paper.
Question: What is a non-biodegradable material ? Give one example.
Answer: A non-biodegradable material is a substance that is not easily broken down by natural processes like the action of bacteria. These materials remain in the environment for a long time.
Example: Plastic.
1. Explain why some fibres are called synthetic.
Answer: Some fibres are called synthetic fibres because they are made by human beings. Natural fibres like cotton, wool and silk come from plants or animals. But synthetic fibres are prepared from chemicals by people in factories. Therefore, they are known as synthetic or man-made fibres.
2. Mark ( Right Sign ) 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.
[ Rayon is made from wood pulp, which comes from plants. That is why it is different from other synthetic fibres that are made only from chemicals. ]
3. Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called __________ or __________ fibres.
(b) Synthetic fibres are synthesised from raw material called __________ .
(c) Like synthetic fibres, plastic is also a __________ .
Answer: (a) Synthetic fibres are also called man-made or artificial 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 fibres are very strong. They are used for making ropes for rock climbing, parachutes and car seat belts. These things need very strong materials. Even a nylon thread is stronger than a steel wire, which shows that nylon fibres are very strong .
5. Explain why plastic containers are favoured for storing food.
Answer: Plastic containers are favoured for storing food because they are light in weight, strong and easy to handle. They are also less expensive and convenient to use. Because of these advantages, plastic containers are commonly used to store water, milk, pickles and dry food.
6. Explain the difference between thermoplastic and thermosetting plastics.
Answer: The Difference between Thermoplastic and Thermosetting Plastics are:
|
Thermoplastics |
Thermosetting Plastics |
|
(i) These plastics soften when heated and can be bent or moulded easily. |
(i) These plastics do not soften on heating and cannot be remoulded. |
|
(ii) They can be reheated and reshaped many times. |
(ii) Once they are set, they cannot be reshaped. |
|
Example: Polythene, PVC |
Example: Bakelite, Melamine |
7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer: (a) Saucepan handles are made of thermosetting plastics because these plastics do not soften on heating. They can tolerate high heat and do not melt easily, so the handles remain safe to hold while cooking.
(b) Electric plugs, switches and plug boards are made of thermosetting plastics like Bakelite because Bakelite is a poor conductor of heat and electricity. This helps to prevent electric shocks and damage due to heat.
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: The categorisation of the materials is:
|
Can be Recycled |
Cannot be Recycled |
|
Plastic toys |
Cooker handles |
|
Carry bags |
Electrical switches |
|
Ball point pens |
Telephone instruments |
|
Plastic bowls |
|
|
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: Rana should buy cotton shirts for summer. Cotton is a natural fibre that absorbs sweat and allows air to pass through easily. This keeps the body cool and comfortable in hot weather. Synthetic fibres do not absorb sweat well, so they may feel uncomfortable in summer.
10. Give examples to show that plastics are noncorrosive in nature.
Answer: Plastics are non-corrosive because they do not react with water and air. For example, plastic containers are used to store water, pickles and many chemicals. Also, plastic pipes are used to carry water and chemicals because they do not rust or get damaged easily like metals.
11. Should the handle and bristles of a tooth brush 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.
The handle should be made of a hard and strong material so that it is easy to hold and does not bend. The bristles should be made of a soft and flexible material so that they can clean the teeth properly without harming the gums.
12. ‘Avoid plastics as far as possible’. Comment on this advice.
Answer: This advice is correct because plastics are non-biodegradable and do not decompose easily in nature. They can cause environmental pollution and harm animals and soil. Burning plastics also releases harmful gases. Therefore, we should reduce the use of plastics and use eco-friendly materials whenever possible.
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: (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: Manufacturing synthetic fibres helps in the conservation of forests because many natural fibres require plants and trees. Synthetic fibres are made from chemical substances instead of plants. So, using synthetic fibres reduces the cutting of trees and use of natural resources, which helps in protecting forests.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer: Take a small electric circuit with a battery, a bulb, and two connecting wires. Keep a small gap in the circuit between the wires. First, connect the gap with a metal object like a paper clip. You will observe that the bulb glows, showing that metal conducts electricity.
Now remove the metal object and place a piece of thermoplastic (like a plastic scale or pen body) in the gap. You will see that the bulb does not glow.
This activity shows that thermoplastic does not allow electric current to pass through it. Hence, thermoplastics are poor conductors of electricity (they are insulators).
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