Synthetic Fibres and Plastics NCERT Solutions Class 8 Science Chapter 3 with Answers

We have Provided the CBSE Solutions chapter-wise. Class 8 Science Chapter 3 Synthetic Fibres and Plastics with Answers by expert subject teacher for latest syllabus and examination. Students can take a free CBSE Solutions of Synthetic Fibres and Plastics. Each question has right answer Solved by Expert Teacher.

CBSE Solutions Class 8 Science Beehive Prose

Page No. 41

Exercise

Q1. Explain why some fibres are called synthetic.

Answer: Some fibres are called as synthetic fibers because these are manmade fibers prepared by using chemicals. These are made of small units that join together to form long chains. Some of the examples of synthetic fibres are nylon, rayon, acrylic, polyester etc.

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..

Answer (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 raw materials called __.
(c) Like synthetic fibres, plastic is also a _.

Answer: (a) artificial or man-made
(b) petrochemicals.
(c) polymer.

Q4. 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.

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

Answer: Plastic containers are most convenient for storing food because:

  • of their lightweight, good strength, lower price, and easy handling.
  • Most importantly plastic containers do not react with the food item that is stored in them, making them safe to store.

Q6. Explain the difference between thermoplastic and thermosetting plastics.

Answer: Thermoplastics can be softened on heating and can be bent easily whereas thermosetting plastics cannot be softened on heating and breaks when forced to bend.

Q7. Explain why the following are made of thermosetting plastics.

(a) Saucepan handles
(b) Electric plugs/switches/plug boards

Answer: (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 Boards: Electric 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.

Q8. Categorize 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: Can be Recycled : Toys, carry bags, plastic bowls, ball point pens, plastic chairs, plastic covering on electrical wires.

Cannot be Recycled : Cooker handles, electrical switches, telephone instruments.

Q9. 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 shirts made from cotton. This is because cotton is a good absorber of water. It can soak the sweat coming out of our body and expose it to the environment. Thus, it helps in evaporating the liquid (sweat), thereby cooling our body.

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

Answer: Plastics are noncorrosive in nature because it is a nonreactive substance. It does not react with air, water, minerals and other chemicals. So in present days most of the containers, utensils and laboratory equipments are made with plastics to store food, chemicals etc.

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

Answer: The handle and bristle of a toothbrush should not be made of the same material as the handle of the toothbrush should be hard and strong while the bristle should be soft and flexible.

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

Answer: Plastics must be avoided as far as possible. The materials made of plastics are non-biodegradable. The use of plastics has a bad effect on the environment. When the plastics are burnt, it releases a lot of poisonous fumes into the atmosphere causing air pollution. These plastic materials when eat up by the animals (like cows), choke their respiratory system. This can cause death of these animals. The waste plastic articles thrown here and there carelessly get into dirty water drains and sewers, and block them. In a nutshell, plastics can be considered a threat to our environment.

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

AB
(i) Polyester
(ii) Teflon
(iii) Rayon
(iv) Nylon
(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

Answer:

AB
(i) Polyester
(ii) Teflon
(iii) Rayon
(iv) Nylon
(d) Fabrics do not wrinkle easily
(d) Fabrics do not wrinkle easily
(a) Prepared by using wood pulp
(b) Used for making parachutes and stockings

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

Answer: It is true that manufacturing synthetic fibers is actually helping conservation of forests. As synthetic fibers are man-made, meaning they are made from chemicals like petrochemicals. Synthetic fibers are artificial fibers that can be made with or without using any natural raw material from plants or animals. Thus their existence has helped in the substitution of natural fibers like cotton, silk, wool, jute which are obtained from plants and animals. So it means that trees need not be cut down for their production, since there is a man-made alternative. This can aid in preventing deforestation as well.

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

Answer: A thermoplastic (or plastic) is a poor conductor of electricity as shown in Fig. 3.3.
If we place a piece of copper in the gap touching points A and B (in Fig. 3.3), we observe that bulb glow. If we place plastic in the gap between A and B, we observe that the bulb will not glow. It means plastic is a poor conductor.

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