Class 8 Science Past Paper Questions PDF

**Question 4.\ Give examples which indicate that nylon fibres are very strong.\ Answer:\ The following examples indicate that nylon fibres are very strong.\ (i) They are used for making parachutes and ropes for rock climbing.\ (ii) They are used in making seat-belts, fishing nets, tyre cord, a strin...

**Question 4.\ Give examples which indicate that nylon fibres are very strong.\ Answer:\ The following examples indicate that nylon fibres are very strong.\ (i) They are used for making parachutes and ropes for rock climbing.\ (ii) They are used in making seat-belts, fishing nets, tyre cord, a string for sports rackets and musical instruments.** **Question 5.\ Explain why plastic containers are favoured for storing food.\ Answer:\ Plastic containers are favoured for storing food because of the following reasons:\ (i) the plastics do not react with the food stored in them.\ (ii) the plastics are lightweight and are strong.\ (iii) they are easy to handle and safe.** **Question 6.\ Explain the difference between thermoplastic and thermosetting plastics.\ Answer:** **Thermoplastics** **Thermosetting plastics** -------------------------------------------------------------------- -------------------------------------------------------------------- **(i) These plastics softened on heating and can be bent easily.** **(i) These plastics when moulded once, can't be softened again.** **(ii) They do not lose their plasticity.** **(ii) They lose their plasticity.** **(iii) Examples are polyethene, PVC, etc.** **(iii) Examples are bakelite and melamine.** **Question 7.\ Explain why the following are made of thermosetting plastics.\ (a) Saucepan handles\ (b) Electric plugs/switches/plugboards\ Answer:\ (a) Since, thermosetting plastics are a bad conductor of heat and do not get heated up while cooking, they are used for making saucepan handles.\ (b) Since thermosetting plastics are a bad conductor of electricity and the electric current does not pass through such plastics, they are used for making electric plugs/switches/plugboards.** **Question 8.\ Categorise the materials of the following products into 'can be recycled' and 'can not be recycled'.\ Telephone instruments, plastic toys, cooker handles, carry bags, ballpoint pens, plastic bowls, plastic covering on electrical wires, plastic chairs, electrical switches.\ Answer:** **Can be recycled** **Cannot be recycled** --------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------- **Plastic toys carry bags, plastic bowls, plastic covering on electrical wires, plastic chairs.** **Telephone instruments, cooker handles, ballpoint pens, 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.\ Answer:\ He should buy cotton shirts. This is because cotton has more capacity to hold moisture than synthetic clothes. In summers we have extensive sweating which is easily soaked by cotton shirts and hence, cotton clothes are much better than the clothes made from synthetic material.** **Question 10.\ Give examples to show that plastics are non-corrosive in nature.\ Answer:\ The literal meaning of non-corrosive is resistant to get destroyed by chemical action.\ Following are the examples that show that plastics are non-corrosive in nature.** - **hey do not get rusted when exposed to moisture and air.** **They do not decompose when left in open for a long period.** **Question 11.** **Should the handle and bristles of a toothbrush be made of the same material? Explain your answer.** **Answer:** **No, the handle and bristles of a toothbrush should not be made of the same material. This is because our gums are soft and the bristles should be made of soft material so that it does not harm the gums. On the other hand, the handles should be made up of hard material so that it can give a firm grip.** **Question 12.** **'Avoid plastics as far as possible'. Comment on this advice.** **Answer:\ 1)Plastics must be avoided as far as possible. The materials made of plastics are non-biodegradable.** **2)The use of plastics has a bad effect on the environment.** **3)When the plastics are burnt, it releases a lot of poisonous fumes into the atmosphere causing air pollution.** **4)These plastic materials when eat up by the animals (like cows), choke their respiratory system. This can cause death of these animals.** **5)The waste plastic articles thrown here and there carelessly get into dirty water drains and sewers, and block them. In a nutshell, plastics can be considered a threat to our environment.** **Question 14.\ 'Manufacturing synthetic fibres is actually helping the conservation of forests'. Comment.\ Answer:\ In the manufacturing of synthetic fibres, we use only chemical substances and no natural materials, thus, in turn, we conserve forests.** **Question 15.\ Describe an activity to show that thermoplastic is a poor conductor of electricity.\ Answer:\ Arrange a circuit as shown in the given figure. Leave a gap between two ends of the wire. Place a thermoplastic in the gap. It is observed that the bulb does not glow. This shows that thermoplastic is a poor conductor of electricity.**