Q 1. Name other natural calamities except lightning and earthquake.
Ans. Winds, storms and cyclones.
Q 2. Mention the interactions of two types of charges.
Ans. Like charges repel each other while unlike charges attract each other.
Q 3. Name the device used to protect buildings from lightning.
Ans. Lightning conductor.
Q 4. What happens when two clouds with unlike charges approach each other?
Ans. Lightning strikes
Q 5. Who discovered the static electricity or lightning in clouds and when?
Ans. Benjamin Franklin in 1752.
Q 6. What happens when amber is rubbed with fur?
Ans. It develops the capacity to attract light objects.
Q 7. What happens when a glass rod and silk cloth are rubbed with each other?
Ans. The glass rod gets positively charged and silk cloth negatively charged.
Q 8. How are most earthquakes caused?
Ans. Most earthquakes are caused by the movement of earth’s plates.
Q 9. How is an earthquake caused?
Ans. It is caused by a disturbance deep inside the earth’s crust.
Q 11. What are the natural calamities caused by earthquakes?
Ans. Earthquakes can cause floods, landslides and tsunamis.
Q 12. Which kind of material is used to transfer charges from one body to another?
Ans. Metal conductor
Q 13. What is lightning? What causes lightning?
Ans. Lightning is also an electric spark, but on a huge scale. It is caused by the accumulation of charges in the clouds.
Q 14. What is an electric charge? What are charged objects?
Ans. When a plastic refill is rubbed with polythene it acquires a small electric charge. Similarly when a plastic comb is rubbed with dry hair, it acquires a small charge. These objects are called charged objects.
Q 15. What do you mean by electric discharge? How does it occurs?
Ans. When the negative and positive charges meet, streaks of bright light and sound are produced. This process is called electrical discharge. For example, electric discharge occurring between two or more clouds or between clouds and earth.
Q 16. How does electric discharge occur in clouds?
Ans. At the time of thunder negative charges are accumulated near the clouds and positive charges near the ground. When these charges meet, electric discharge takes place between the ground and clouds. In this process, a large amount of energy is released.
Q 17. What is an earthquake? How is it caused?
Ans. Sudden shaking and trembling of earth is called an earthquake. It is caused mostly due to the movement of earth’s plates inside the crust.
Q 18. What are fault zones? Name the fault zones in India.
Ans. Since earthquakes are caused by the movement of plates, the boundaries of the plates are weak zones where earthquakes are more likely to occur. The weak zones are also known as seismic or fault zones.
Q 20. In India the most threatened areas or fault zones are Kashmir, Western and Central Himalayas, the Indo-Gangetic Plain, Rann of Kutch, etc.
Ans. Tremors on the earth can also be caused when a volcano erupts, or a meteor hits the earth, or an underground nuclear explosion is carried out.
Q 21. What are seismic waves? How are these waves recorded?
Ans. The tremors produce waves on the surface of the earth. These are called seismic waves. These waves are recorded by an instrument called the seismograph.
Q 22. What is lightning? How does lightning strike?
Ans.
Lightning is an electric spark, but on a huge scale. It is caused by the accumulation of charges in the clouds.
When two clouds carrying opposite charges come very close to each other, the charges flow with great speed from one cloud to another through the air between them. Consequently, a very bright spark is produced. The spark caused due to the transfer of electric charge between two clouds causes lightning. It can occur when electric charges flow from one part of a cloud to another or from a cloud to the ground. Lightning is accompanied by large amounts of electric charges and very high temperatures. The huge amount of heat produced makes the air expand very suddenly what causes vibration to occur, resulting in a loud sound called thunder.
Q 23. Explain the process of electric discharge.
Ans. During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. By a process, the positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower 1 edges. There is accumulation of positive near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Finally negative and positive charges meet, producing streaks of bright light and sound called lightning and thunderstorm respectively. This process is known as electric discharge. This can occurs between two or more clouds, or between clouds and the earth.
Q 24. What are the measures we should adopt to protect against an earthquake?
Ans. We know that earthquakes cannot be predicted. It is, therefore, important that we should take necessary precautions to protect ourselves all the time as given below:
- In seismic zones it is advisable to make the structure of the buildings simple so that it is ‘Quake Safe’. Modern building technology can make it possible.
- In highly seismic areas, the use of mud or timber is better than using heavy construction materials.
- Since some buildings may catch fire, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order.
- If we are at home, we should take shelter under a table and stay there till the shaking stops. We should stay away from tall and heavy objects that may fall on us. If we are in bed, we should protect our head with a pillow.
- If we are at outdoors, we should find a clear spot, away from buildings, trees and overhead power lines and drop to the ground. If travelling in a car or a bus, do not come out and drive slowly to a clear spot.
Q 25. If aluminium strips of an electroscope are replaced by plastic strips and a charged body is brought in contact with the metal clip. What will happen?
Ans. The plastic strips will show repulsion. Charges from the charge body will be transfer from the metal rod to the plastic strips. As a result, similar charges will develop on the plastic strips and repulsion will occur
Q 26. If a charged plastic straw is brought near another uncharged plastic straw, what will happen?
Ans. They will attract each other due to presence of unlike charges on them.
Q 27. If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.
Ans. If air and cloud were good conductors of electricity then charge separation will not take place and hence lightning will not occur.
The strips of an electroscope diverge when a charged body is brought in contact with the metal clip.
Q 28. What will happen to the strips if we gently touch the metal clip with our hands?
Ans. The strips will collapse due to discharging of the charges through our hand.
Q 29. On a dry day, why do you get a slight shock on touching the screen of a television or computer monitor (with a picture tube)?
Ans. Electric charges accumulated on the screen of television or computer monitor get discharged through our body. Thus, we get a slight shock.
Q 30. What safety measures should be taken during lightning and thunderstorm?
Ans. The following safety measures are advisable to be adopted to protect from lightning and thunderstorm:
- No open place is safe. A house or a building is a safe place. If travelling by car or by bus, it is safe to stay inside with windows and doors of the vehicle shut.
- If we are outside, the following things are important to be kept in mind:
- Open vehicles, like motorbikes, tractors, construction machinery, fields, tall trees, shelters in parks, elevated places do not protect us from lightning strikes.
- Carrying an umbrella is not at all a good idea during thunderstorms.
- If no shelter is available and we are in an open field, we should keep away from all trees. We should stay away from poles or other metal objects. We should not lie on the ground. Sitting in a pose as given in the Fig. 15.8 is advisable.
- If we are inside the house, we should take care as advised further:
Lightning can strike telephone cords, electrical wires and metal pipes. During a thunderstorm, contact with these should be avoided.
It is safer to use mobile phones and cordless phones. However, it is not wise to call up a person with a wired phone. Bathing should be avoided. Electrical appliances should be unplugged.
Q 31. What is a lightning conductor? How does it work?
Ans.
Lightning conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the buildings during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground as shown in the figure. The rod provides easy route in the transfer of electric charge to the ground.
The metal columns used during construction, electrical wires and water pipes in the buildings also protect us to an extent. But we should not touch them during thunderstorm.
Q 32. What is an earthquake? What causes an earthquake?
Ans. An earthquake is a sudden shaking or trembling of the earth. It lasts for a very short time. It is caused by a disturbance deep inside the earth’s crust.
We know that tremors are caused by the disturbance deep down inside the uppermost layer of the earth called crust (Fig. 15.10). The outermost layer of the earth is fragmented. Each fragment is called a plate (Fig. 15.11). These plates are in continual motion. When they brush one another, or a plate goes under another due to collision (Fig. 15.12), they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.
Q 33. Make your own charge detector. Take a paper strip roughly 10 cm x 3 cm. Give it a shape as shown in Fig. 15.7. Balance it on a needle. Bring a charged body near it. Observe what happens. Write a brief report, explaining its working.
Ans.
When we touch one side of the paper with a charged body, paper strips will open. This is due to the two sides of paper strips get the same type of charge from the charged body and they repel each other.
Q 34. What damage is caused by lightning?
Ans. When lightning strikes a tree, it can burn up the tree. And when a person is hit by lightning during a thunderstorm, then electric energy passes through the body of the person due to which the person get severe burns and get killed. Thus, it can cause a lot of destruction by damaging property, trees and killing people.
Q 35. How can we determine if an object is charged or not?
Ans. An electroscope may be used to detect whether a body is charged or not. When the object is touched with the metal cap of an electroscope, both the metal cap and the leaves acquire the same charge from the charged object through the paper clip. It will cause the leaves to diverge showing that the object was charged.
Q 36. What is lightning conductor? How does it work?
Or
How does a lightning conductor protect a tall building
Ans. Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground.
Q 37. What are the various effects of an earthquake?
Ans. The various effects of an earthquake are:
- They can cause immense damage to buildings, bridges, dams and people. There can be a great loss to life and property.
- The earthquakes can cause floods, landslides and tsunamis.
- A major tsunami occurred in the Indian Ocean on 26th December 2004. All the coastal
areas around the ocean suffered huge losses.
Q 38. What will you do to protect yourself from lightning if you are in an open field?
Ans. If no shelter is available and we are in an open field, we should stay far away from all trees. We should stay away from poles or other metal objects. We should not lie on the ground instead we should squat low on the ground. We should place our hands on our knees with our head between the hands. This position will make us the smallest target to be struck.
Q 39. Explain why a charged balloon is repelled by another charged balloon
whereas an uncharged balloon is attracted by another charged balloon?
Ans. A charged balloon is repelled by another charged balloon because both the balloons have same type of charges and like charges repel each other. Whereas an uncharged balloon is attracted by another charged balloon because charged balloon induces opposite charges in the nearer end of the uncharged balloon by electric induction and unlike charges attract each other.
Q 40. Suppose you are outside your home and an earthquake strikes. What
precaution would you take to protect yourself?
Ans. If we are outside our home and an earthquake strikes, then
- We should try to find a clear spot, away from buildings, trees and overhead power lines.
Drop to the ground. - If we are in a car or a bus, we should not come out. We should ask the driver to drive
slowly to a clear spot. We should not come out till the tremors stop.