Class.8-Chapter.3-Synthetic Fibres & Plastics -NCERT Solutions
Question 1
Some fibres are called synthetic. Why
Some fibres are called synthetic. Why
Answer
Some fibres are made in factories and hence they are called synthetic.
Some fibres are made in factories and hence they are called synthetic.
Question 2
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
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
(b) It is obtained from wood pulp
Question 3
Fill in the blanks with appropriate words:
(a) Synthetic fibres are also called ______ or _______ fibres.
(b) Synthetic fibres are synthesized from raw material called ________.
(c) Like synthetic fibres, plastic is also a __________ .
Fill in the blanks with appropriate words:
(a) Synthetic fibres are also called ______ or _______ fibres.
(b) Synthetic fibres are synthesized from raw material called ________.
(c) Like synthetic fibres, plastic is also a __________ .
Answer
a) man-made or artificial
b) petrochemicals
c) polymer
a) man-made or artificial
b) petrochemicals
c) polymer
Question 4
Give examples which indicate that nylon fibres are very strong.
Give examples which indicate that nylon fibres are very strong.
Answer
Nylon is used in making ropes which are used for heavy-duty purposes; like mountaineering and in parachute. These usages show that nylon fibres are very strong.
Nylon is used in making ropes which are used for heavy-duty purposes; like mountaineering and in parachute. These usages show that nylon fibres are very strong.
Question 5
Explain why plastic containers are favoured for storing food.
Explain why plastic containers are favoured for storing food.
Answer
1. Plastic is a non-reactive and non-corroding material.
2. Plastic containers do not change the flavour or quality of food.
3. They are light weighted and easy handling is possible with them Due to this, plastic containers are favoured for storing food.
1. Plastic is a non-reactive and non-corroding material.
2. Plastic containers do not change the flavour or quality of food.
3. They are light weighted and easy handling is possible with them Due to this, plastic containers are favoured for storing food.
Question 6
Explain the difference between the thermoplastic and thermosetting plastics.
Explain the difference between the thermoplastic and thermosetting plastics.
Answer
|
Thermoplastic
|
Thermosetting plastic
|
|
The shape of
thermoplastic can be easily changed by heating again
|
The shape of thermosetting
plastic cannot be altered once it has been mould into a particular shape
|
|
Thermoplastic
is used in making toys, combs, containers, etc.
|
Thermosetting
plastic is used for making those items which need to withstand high
temperature; such as handles of cooking utensils
|
Question 7
Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Explain why the following are made of thermosetting plastics.
(a) Saucepan handles
(b) Electric plugs/switches/plug boards
Answer
|
Saucepan
handles
|
Saucepan
handles have to withstand high temperature during cooking and thermosetting
plastic is ideal for that. Also they are bad conductor of heat
|
|
Electric
plugs/switches/plug boards
|
Electric
plugs/switches/plug-boards need to be durable and should withstand continuous
use over many years. Moreover, in case of some heating due electric current;
they should not melt. Hence, these devices are made from thermosetting
plastic.
Also they are bad conductor of heat and electricity |
Question 8
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)
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
|
Plastic toys,
carry bags, ball point pens, plastic bowls, , plastic covering on electrical
wires, plastic chairs
|
|
Cannot be
recycled
|
Telephone
instruments, cooker handles, electrical switches
|
Question 9
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Rana wants to buy shirts for summer. Should he buy cotton shirts or shirts made from synthetic material? Advise Rana, giving your reason.
Answer
Cotton has better absorbent property than synthetic fibre. During summer, cotton cloth can absorb sweat. The sweat would give cooling effect to the body, due to evaporation. Thus a cotton shirt would be much more comfortable than a shirt made from synthetic fibre. Hence, Rana should buy cotton shirts for summer.
Cotton has better absorbent property than synthetic fibre. During summer, cotton cloth can absorb sweat. The sweat would give cooling effect to the body, due to evaporation. Thus a cotton shirt would be much more comfortable than a shirt made from synthetic fibre. Hence, Rana should buy cotton shirts for summer.
Question 10
Give examples to show that plastics are non corrosive in nature.
Answer
a. Pickles usually come packed in plastic sachets or glass bottles. Pickles contain acids, yet no harm is done to the plastic sachet.
b. Sanitary cleaners and some acids; which are used as bathroom cleaner are sold in plastic bottles.
The above examples show non-corrosive nature of plastic.
Give examples to show that plastics are non corrosive in nature.
Answer
a. Pickles usually come packed in plastic sachets or glass bottles. Pickles contain acids, yet no harm is done to the plastic sachet.
b. Sanitary cleaners and some acids; which are used as bathroom cleaner are sold in plastic bottles.
The above examples show non-corrosive nature of plastic.
Question 11
Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.
Answer
The handle and bristles of a tooth brush should be made of different materials as they server different purpose
Material which is used for making toothbrush handle should be hard and flexible as the handle has to withstand lot of stress and has to reach every corner of mouth.
Material which is used for making bristles should be soft, flexible yet durable as the bristles should not damage the tooth or gum but should last longer.
The handle and bristles of a tooth brush should be made of different materials as they server different purpose
Material which is used for making toothbrush handle should be hard and flexible as the handle has to withstand lot of stress and has to reach every corner of mouth.
Material which is used for making bristles should be soft, flexible yet durable as the bristles should not damage the tooth or gum but should last longer.
Question 12
‘Avoid plastics as far as possible’. Comment on this advice.
‘Avoid plastics as far as possible’. Comment on this advice.
Answer
Plastic has gained popularity because of its versatile nature. But because of its unmatched popularity; in terms of variety of usage; it has turned into a curse as well. Here are some of the disadvantages
a. We are creating too much of plastic waste around us.
b. Plastic is non-biodegradable and many forms of plastic cannot be recycled. This is creating a burden on the environment around us. They take several years to decompose
c. They cannot be easily burnt and if burnt release poisonous gas
Hence, the statement, “Avoid plastics as far as possible” is a correct statement.
Plastic has gained popularity because of its versatile nature. But because of its unmatched popularity; in terms of variety of usage; it has turned into a curse as well. Here are some of the disadvantages
a. We are creating too much of plastic waste around us.
b. Plastic is non-biodegradable and many forms of plastic cannot be recycled. This is creating a burden on the environment around us. They take several years to decompose
c. They cannot be easily burnt and if burnt release poisonous gas
Hence, the statement, “Avoid plastics as far as possible” is a correct statement.
Question 13
Match the terms of column I correctly with the phrases given in column II.
Match the terms of column I correctly with the phrases given in column II.
Answer
|
Column I
|
Column II
|
|
Polyester
|
Fabrics do not wrinkle easily
|
|
Teflon
|
Used to make non stick cookware
|
|
Rayon
|
Prepared by using wood pulp
|
|
Nylon
|
Used for making parachutes and stockings
|
Question 14
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
‘Manufacturing synthetic fibres is actually helping conservation of forests’. Comment.
Answer
Forests provide many important raw materials from which we make various useful items. This means we have to cut lot of trees which means deforestation. Many things which were earlier made from forest produce are now being made from synthetic fibres.
Examples
1. plastic chairs have replaced wooden chairs in a big way.
2. wooden cartons and crates have been replaced by plastic cartons and crates.
The way plastic has replaced wood from many items, it is definitely minimizing the need to cut forests. Thus, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.
Forests provide many important raw materials from which we make various useful items. This means we have to cut lot of trees which means deforestation. Many things which were earlier made from forest produce are now being made from synthetic fibres.
Examples
1. plastic chairs have replaced wooden chairs in a big way.
2. wooden cartons and crates have been replaced by plastic cartons and crates.
The way plastic has replaced wood from many items, it is definitely minimizing the need to cut forests. Thus, it can be said that manufacturing synthetic fibres is actually helping conservation of forests.
Question 15
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Describe an activity to show that thermoplastic is a poor conductor of electricity.
Answer
For this, take a discarded plastic toy, a torch which is in working order. Switch the torch on to check that it is in working condition. From the plastic toy, cut a small piece about the size of a coin. Now insert this coin between two cells of the torch. Then tighten the lid of the torch. Now, switch on the torch. You will notice that the bulb does not glow. This happens because the plastic coin; between two cells; does not allow current to pass between two cells. This shows that thermoplastic is a poor conductor of electricity.
For this, take a discarded plastic toy, a torch which is in working order. Switch the torch on to check that it is in working condition. From the plastic toy, cut a small piece about the size of a coin. Now insert this coin between two cells of the torch. Then tighten the lid of the torch. Now, switch on the torch. You will notice that the bulb does not glow. This happens because the plastic coin; between two cells; does not allow current to pass between two cells. This shows that thermoplastic is a poor conductor of electricity.
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