NCERT Solutions for Class 8 Science Chapter 3 Synthetic Fibres and Plastics are prepared by subject professionals and it includes solutions to all the questions present in the NCERT Class 8 Science Textbook. All the NCERT Solutions are framed in a systematic manner, according to the latest CBSE Class 8 Science syllabus (2020-21).
The solution has answers to the questions on Synthetic Fibres and Plastics, their source, their uses, different types of fibres, natural fibres, artificial fibres, uses and qualities of plastics, problems caused due to waste produced by plastics, proper usage of fibre and plastics.
After studying NCERT Solutions you will be able to understand the topics covered in the chapter thoroughly. It is noticed that many questions are directly asked in previous year Class 8 examinations. In order to score good marks in the examination, students should study this material in-depth.
Exercises, Page - 41
1. Explain why some fibres are called synthetic.
Answer:
Some fibres are called as synthetic fibres because these are man-made fibres prepared by using chemicals. These are made of small units that join together to form long chains. Some of the examples of sunthetic fibres are nylon, rayon, acrylic, polyester etc.
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.
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) artificial, man-made
(b) petrochemicals
(c) polymer
4. Give examples which indicate that nylon fibres are very strong.
Answer:
Following are the examples which indicate nylon fibres are very strong :
- Parachutes and ropes of rock climbing are made of nylon
- Nylon is used in making seat belts, fishing nets and tyre cords
- Nylon is used in making sports accessories like racket.
5. Explain why plastic containers are favoured for storing food.
Answer:
Because plastic is non-reactive and will not react with the ingredients of the food items.
6. Explain the difference between thermoplastic and thermosetting plastics.
Answer:
The difference between thermosetting and thermoplastic are -
Thermosetting plastic :
- Cannot be bent, it will break if we attempt to be bend thermosetting plastic
- On heating thermosetting plastics, it cannot be softened. This is the reason it can not be reshaped once it is molded.
Thermoplastic :
- Thermoplastic can be bent easily.
- On heating the thermoplastics, it becomes softened and can be molded and reshaped easily.
7. Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer:
(a) Thermosetting plastics are used to make saucepan handles because they are bad conductors of heat and also on heating, these plastics do not get softened.
(b) Bakelite is a kind of thermosetting plastic which is a bad conductor of heat and electricity. Because of this property it is used for making electric plugs, switches, plug boards etc.
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:
Can be recycled :
Platic chairs, plastic bowls, plastic toys, The plastic covering on electrical wires, carry bags, ball point pens
Cannot be recycled :
Cooker handles, electrical switches, telephone
9. Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic materials ? Advise Rana, giving your reason.
Answer:
Rana should buy a cotton shirt for the summer and not a synthetic shirt. Cotton is a good absorber of water. So it can soak the sweat coming out of the body and expose it to the environment. Thus, it helps in evaporating the sweat and helps in cooling our body.
10. Give examples to show that plastics are noncorrosive in nature.
Answer:
Plastics are non corrosive in nature, they do not react even if they come in contact with strong chemicals. For example, the cleaning chemicals that we use at home are stored in plastic bottles, instead of metal containers.
11. 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 tooth brush 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.
12. 'Avoid platics as far as possible'. Comment on this advice.
Answer:
We should avoid plastics as far as possible because plastics are non biodegradable in nature. Once introduced into the environment they cause pollution. If burnt they release poisonous gases and the plastic bags thrown in the garbage dumb are swallowed by animals choke their respiratory system and causes fatalities in animals.
13. Match the terms of column A correctly with the phrases given in column 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:
The manufacturing of synthetic fibres is the helpful in the conservation of forests because if we use natural fibres, the raw materials for them have to be derived from the plants, which require cutting off lots of trees. This proves to be helpful in the conservation of the forests.
15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer:
In order to show that thermoplastic is a poor conductor of electricity, we will design a circuit. For that, we need a bulb, some wires, a battery, a piece of metal and a plastic pipe (as shown in the figure below). After setting the experiment switch on the current, you will observe that the bulb glows in the former case. In the latter case, the bulb does not glow . Hence a plastic pipe (which is a thermoplastic) is shown to be a poor conductor of electricity.
