Andhra Pradesh SCERT Class 8 Semester 1 Physical Science chapter 4 Synthetic Fibres and Plastics
Andhra Pradesh SCERT has recently updated its curriculum and a new semester system has been introduced in the course. Here we have provided complete solutions according to the new semester-wise syllabus. In this page you will find complete solutions of the 4th chapter Synthetic Fibres and Plastics of physical science class 8.
Board |
Andhra Pradesh SCERT |
Class |
8 |
Subject |
Physical Science |
Semester |
1st |
Chapter |
4: Synthetic Fibres and Plastics |
1.) Explain why some fibres are called synthetic.
Ans: Synthetic fibres are those fibres that are made artificially in other words man made. Fibres like rayon and nylon are example of synthetic fibres.
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.
3.) Fill in the blanks with appropriate words.
(a) Synthetic fibres are also called (?) or (?) fibres.
Ans: Synthetic fibres are also called artificial or man-made fibres.
(b) Synthetic fibres are synthesised from raw material called (?).
Ans: Synthetic fibres are synthesised from raw material called petrochemicals.
(c) Like synthetic fibres, plastic is also a (?).
Ans: Like synthetic fibres, plastic is also a polymer.
4.) Give examples which indicate that nylon fibres are very strong.
Ans: Nylon fibres are used in making ropes for rock climbing and parachutes. This indicates that the nylon fibres are very strong.
5.) Explain why plastic containers are favoured for storing food.
Ans: there are numerous reasons why plastics are favoured for storing food. Plastics are lightweight, sturdy and cost effective. They can be moulded into any beautiful and convenient shapes. Another man reason is that the plastics are not very reactive so they do not react with the food which makes a very safe option. These are the reasons why plastic containers are favoured for storing foods.
6.) Explain the difference between thermoplastic and thermosetting plastics.
Ans: Thermoplastics are a variety of plastic that easily gets deformed on heating. This material is used to make plastic bottles and toys. PVC and Polythene are examples of thermoplastics.
On the other hand thermosetting plastics do not get affected by heating once it is moulded. These kinds of plastics are used to make electrical equipment and kitchen appliances making them more fire resistant. Bakelite and melamine are examples of thermosetting plastic.
7.) Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
Ans: The thermosetting plastics do not change their shape or compromise their structural integrity under heat once it is moulded. The saucepan gets extremely hot while cooking. For that reason the handle of the saucepan must withstand that heat without getting deformed. Thermosetting plastics are also bad conductor of heat so even when the pan gets hot the handle stays cool and useable.
(b) Electric plugs/switches/plug boards
Ans : As we already know that the thermosetting plastics are poor conductor of heat and do not react to heat after its moulded. Electric plugs, switches and plug boards are designed to withstand extreme heat to prevent any fire. Bakelite is a type of thermosetting plastic that is used to make electrical equipments.
8.) Categorise the materials of the following products into ‘can be recycled’ and ‘cannot be recycled’.
Ans: Here we have categorised the given products into two categories can be recycled and cannot be recycled
Can be Recycled |
Cannot be Recycled |
1) Plastic toys |
1) Telephone instruments, |
2) Carry bags, |
2) Cooker handles |
3) Ball point pens |
3) Electrical switches. |
4) Plastic bowls, |
|
5) Plastic covering on electrical wires |
|
6) 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.
Ans: Rana should buy cotton shirt for the summer use.
The reason is cotton cloth can absorb water more efficiently than synthetic cotton. So the cotton can absorb the sweat released by body during summer making it more comfortable. This can be tested by putting one synthetic and one cotton cloth in two bowls of water. We would see that the cotton cloth absorbed more water than the synthetic cloth.
10.) Give examples to show that plastics are noncorrosive in nature.
Ans: Plastics are not very reactive material. They do not react with its surroundings. For example plastic bags take around 20 years to decompose when left in the open. This proves that plastics are noncorrosive in nature.
11.) Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Ans: The handle and the bristles of a tooth brush should not be made with the same material. If they were made of same material it would become useless. The handle of a toothbrush must be strong and sturdy for a better control of the brush. On the other hand the bristles of the brush must be flexible and bendy so they do not hurt our gums or teeth. They both need different kind of plastics for their different purpose. Handles are made from plastics for their sturdiness and the bristles are made from nylon for their flexibility.
12.) ‘Avoid plastics as far as possible’. Comment on this advice.
Ans: The advice given above is a very good advice if we want to stop polluting the earth. Plastics do not degenerate completely in the nature as they are noncorrosive. After hundreds of year plastics turn into small microscopic piece of plastics and keep polluting the atmosphere.
13.) Match the terms of column A correctly with the phrases given in column B.
Column A |
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 cookware |
(iv) Nylon |
(d) Fabrics do not wrinkle easily |
Column A |
Column B |
(i) Polyester |
(d) Fabrics do not wrinkle easily |
(ii) Teflon |
(c) Used to make non-stick cookware |
(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.
Ans: In some ways we can say that manufacturing synthetic fibres is actually helping in conservation of forests. Synthetic fibres like polyester and nylon are completely man made products. They are not acquired from animals or from forests. This fights the deforestation to some extent.
15.) Describe an activity to show that thermoplastic is a poor conductor of electricity.
Ans: The coverings of the electrical wires have plastic covers which show that they are poor conductor of electricity.
Also See: Andhra Pradesh Class 8 Physical Science Chapter 3 Solutions