Ncert solution class 8 science ch 3 Synthetic Fibres and Plastics.

Ncert solution class 8 science ch 3 Synthetic Fibres and Plastics.
science book

questions 1 to 5.

Q 1. Explain why some fibres are called synthetic.
AnswerThere are some fibers that are made by humans using chemicals. These are called synthetic fibers. These are made up of small units that join together to create long chains. Examples of synthetic fiber are rayon, nylon, polyester, acrylic, etc.

Q 2. Mark the correct answer.
rayon is different from synthetic fibres because:
Answer:  it is obtained from wood pulp.

Q 3. Fill in the blanks:-
Answer: (a) artificial and man made
(b) petrochemicals
(c) polymer

Q 4.Give example which indicate that nylon fibres are very strong.
AnswerNylon fibers are very strong. It is used to make ropes to climb the rocks and
To create a parachute. Their use shows that the nylon fiber has high tensile strength.

Q 5.Explain why plastics container are favoured for storing food.
AnswerThere are features to make plastic friendly to store food items:
(i) Light weight
(ii) Low cost
(iii) good strength
(iv) Easy Handling

 questions 6 to 10.

Q 6. Explain the difference between thermoplastic and thermosetting plastics.
Answer: Thermosetting plastic:- it cannot be bent cannot be softened by heating so,it cannot be reshaped once moulded.
Thermo plastic:- it can be bent can be softened by heating so,it can be reshaped.

Q 7.Explain why the followings are made of thermosetting plastics.
Answer: (a) Saucepan handles:-it is made of thermostate plastics because these plastics are not soft on heating. Apart from this, thermosetting such as backlit is a bad conductor of plastic heat.
(b) Electric plugs/switches/plug boards:-The thermostat, such as Beclight, is a poor conductor of heat and electricity. Therefore, they are used to make electrical plugs, switches, plug boards,

Q 8.Categorize the material of the following product into ‘can be recycled’ and ‘cannot be recycled’.
Answer: cannot be recycled:- Telephone instrument, Cooker handle, Electrical switch.
Can be recycled:- plastics toys, plastic chairs,carry bags,ball point pens,plastic covering on electrical wire,plastic bowls.

Q 9.Rana want to buy shirt for summer. 
Should he buys cotton shirts or shirts made from synthetic material? 
Advise Rana, giving your reason.
Answer: Rana should buy cotton shirts. This is because cotton is a good absorber of water. It is sweating from our body and can expose it to the environment. Thus, this liquid helps in evaporation, which causes our body to cool down.

Q 10.Give example to show that plastics are non-corrosive in nature.
Answer: Plastic is not spoiled even when exposed to strong chemicals. This is due to their non-responsive nature with most materials. For example, cleaning chemicals used at home are kept in plastic bottles instead of metal containers.

 question 11 to 15.

Q 11.Should the handle and bristle of a tooth brush be made of the same material?
Explain your answer.
AnswerNo. Tooth brush handles and Bristol are made up of different materials. Toothbrush should be hard and strong, while Bristol should be soft and flexible.

Q 12. ‘Avoid plastics as far as possible’. Comment on this advice.
AnswerPlastics are non-biodegradable. After appearing once in the environment, they take many years to disintegrate. Plastic add to environmental pollution. When burnt, they can not be burnt, they release toxic gases. Plastic bags thrown in the garbage dump are swallowed by animals like cows. These plastic bags suppress their respiratory system and can prove deadly. Therefore, we should avoid plastic as much as possible.

Q 13. Match the following .
     Column I                         Column II
(i) polyster ----------------- fabrics do not wrinkle easily.
(ii) Teflon-------------------- used to make non-stick cookware.
(iii) Rayon------------------- prepared by using wood pulp.
(iv) Nylon--------------------- used for making parachutes and stockings.

Q 14.‘Manufacturing synthetic fibre is actually helping conservation of forests’. Comment.
AnswerRaw materials mainly for natural fiber are obtained from plants and this means that many trees are used for cutting. It leads to deforestation. But raw materials of synthetic materials are mainly petrochemicals. Therefore, construction synthetic fiber helps in the conservation of the forest.

Q 15. Describe an activity to show that thermoplastic is a poor conductor of electricity.
AnswerWe will prepare a circuit to see that thermoplastic is a poor operator of electricity.
We need bulbs, some strings, a battery, a piece of metal, and a plastic pipe. Set the circuit with metal and then with plastic pipes (as shown in Figures).
After turning on, you will see that the bulb shines in the prior case. In the latter case, the bulb does not shine. Therefore, a plastic pipe (which is thermoplastic) is considered a poor cone.


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