Gujarat Board GSEB Textbook Solutions Class 8 Science Chapter 3 Synthetic Fibres and Plastics Textbook Questions and Answers, Notes Pdf.
Gujarat Board Textbook Solutions Class 8 Science Chapter 3 Synthetic Fibres and Plastics
Gujarat Board Class 8 Science Synthetic Fibres and Plastics Textbook Questions and Answers
Explain why some fibres are called synthetic.
Some fibres are called synthetic fibres because they do not occur in the nature.
Tick (4) 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.
(b) It is obtained from wood pulp.
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 ______
(a) man-made, artificial.
Give examples which indicate that nylon fibres are very strong.
Nylon fibres are strong, so they are used for making parachutes and ropes for rock climbing.
Explain why plastic containers are favoured for storing food.
Advantages of plastic containers:
- Plastics do not react with food items.
- Plastics are strong and light.
- They are easy to handle and safe.
Explain the differences between thermoplastics and thermosetting plastics.
- These are the plastics which get deformed easily on heating and can be bent easily.
- Examples: Polythene and PVC.
- These are used for manufacturing toys, combs, car grills and various types of containers.
- These are the plastics which when moulded once, cannot be softened by heating.
- Examples: Bakelite and Melamine.
(a) Bakelite is used for making electrical switches, handles of various utensils etc.
(b) Melamines are used for making floor tiles, kitchenware and fabrics, which resist fire.
Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
(a) The saucepan handles are made of thermosetting plastics, because it is a bad conductor of heat and do not get heated up while cooking.
(b) Electric plugs/switches/plug boards are made up of thermosetting plastics, because it is a bad conductor of electricity. Electric current does not pass through such plastics.
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.
Can he recycled: Toys, carry bags, plastic bowls, ball point pen, plastic chairs, electric wire covering.
Cannot be recycled: cooker handles, electric switches, telephone instruments.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Rana should buy cotton shirts for summer because cotton is a bad conductor of heat. It does not allow the transmission of heat from or to the body, thus protects body from heat. It also has more capacity to hold moisture than the synthetic clothes. So, it retains the sweat of the body and keep it cool.
Give examples to show that plastics are noncorrosive in nature.
Plastics are noncorrosive in nature:
- They do not react with any substance.
- Plastics do not react with air and water, which are essential for corrosion.
- They do not show any chemical reaction.
Should the handle and bristles of a toothbrush be made of the same materials? Explain your answer.
No, handle and toothbrush bristles should not be made of same material. This is because, handle needs to be hard, while bristle’s need to be soft. Handle should be made up of a material which provides firm grip and bristles should be made up of soft material, which do harm the teeth.
‘Avoid plastics as far as possible’. Comment on this advice.
Plastics are non-biodegradable materials. So use of plastics is harmful for our environment. Plastics cannot be completely disposed off. Thus, plastics should be avoided as far as possible.
Match the terms of Column A correctly with the phrases given in Column B.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Natural fibres required the raw materials from plants and animals. So they required cutting of trees and killing of animals. Synthetic fibres are made up of chemicals and these chemicals are synthesised in laboratory. So manufacturing synthetic fibres helps in actually conservation of forests.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Observe some electrical wires. They have a plastic covering over them, which do not conduct electricity. Also handles of screw drivers are made up of a plastic. These observations show that plastics are poor conductor of electricity.