Q 1 – The process of transfer of charges from a charged object to the earth is called
(a) earthing
(b) lightning
(c) oscillation motion
(d) electron movement
Ans. (a) earthing
Q 2 – Which is not a natural phenomena?
(a) Earthquakes
(b) Cyclones
(c) Lightning
(d) Earthing
Ans. (d) Earthing
Q 3 – Lightning always follows
(a) a thunder
(b) rain pour
(c) the easiest path
(d) a straight path
Ans. (a) a thunder
Q 4 – Which is the surest test of charge on a body?
(a) Repulsion
(b) Lightning
(c) Combustion
(d) Insulation
Ans. (a) Repulsion
Q 5 – Which of the following can be charged by rubbing?
(a) Ebonite
(b) Plastic
(c) Amber
(d) All of these
Ans. (d) All of these
Q 6 – A device used to test whether an object is carrying charge or not is called ______.
(a) Electrometer
(b) Charge meter
(c) Electroscope
(d) Chargoscope
Ans. (c) Electroscope
Q 7 – To protect tall buildings from the damage of lightning, what can be done?
(a) Not to build tall buildings
(b) Install lightning conductors
(c) Install many TV antennas
(d) Have a roof top garden with tall trees
Ans. (b) Install lightning conductors
Q 8 – The power of an earthquake is expressed in terms of magnitude on a scale called
(a) Righter Scale
(b) Quake scale
(c) Richter Scale
(d) Earth Scale
Ans. (c) Richter Scale
Q 9 – The process of transferring charge from a charged body to earth is called
(a) transferring
(b) Processing
(c) Charging
(d) Earthing
Ans. (d) Earthing
Q 10 – During a thunderstorm which action may be done?
(a) Using Telephone having cord
(b) Switching on / off electric lights
(c) Using a mobile phone
(d) None of the above
Ans. (c) Using a mobile phone
Q 11 – It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as __________
(a) Negative
(b) Positive
(c) Neutral
(d) Can be any one
Ans. (b) Positive
Q 12 – Earthquake of which magnitude of the following cause the maximum damage?
(a) 3.0
(b) 8.0
(c) 5.0
(d) 4.0
Ans. (b) 8.0
Q 13 – Types of charges gained by rubbing objects are
(a) 3
(b) 2
(c) 4
(d) 1
Ans. (b) 2
Q 14 – Which of the following is not likely to cause tsunami?
(a) Nuclear explosion under sea
(b) Earthquake
(c) Volcanic eruption
(d) Lightning
Ans. (d) Lightning
Q 15 – If two charged objects are brought close to each other then
(a) they will attract each other.
(b) they will repel each other.
(c) they may attract or repel depending on the charges they carry.
(d) there will be no effect between them.
Ans. (c) they may attract or repel depending on the charges they carry.
Q 16 – The like charges
(a) repel each other
(b) attract each other
(c) no interaction takes place
(d) all of these
Ans. (a) repel each other
Q 17 – The epicenter of an earthquake is located
(a) deeper under the crust of the earth
(b) in the mantle of the earth
(c) on the surface of the earth
(d) in the core of the earth
Ans. (c) on the surface of the earth
Q 18 – The SI unit of electric charge is
(a) watt
(b) joule
(c) coulomb
(d) ampere
Ans. (c) coulomb
Q 19 – As per convention, what is the charge on a glass rod when it is rubbed with a silk cloth?
(a) Positive
(b) Negative
(c) Either (a) or (b)
(d) No charge
Ans. (a) Positive
Q 20 – What are the two natural calamities?
Ans.
- Lightning and
- Earthquake.
Q 21 – Name the two types of charges.
Ans.
- Positive; and
- Negative.
Q 22 – 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 23 – 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 24 – 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 25 – 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 26 – 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 27 – 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 28 – 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 29 – During construction of a building, the lightning conductor was a little shorter and cannot be buried in the ground. Would the lightning conductor be still effective? Explain.
Ans. No, it will not be effective. Since lightning conductor was not connected properly to the earth, therefore, the charge will not pass through to the earth.
Q 30 – n a dry day why do you get a slight shock on touching the screen of a television or computer monitor (with picture tube)?
Ans. Electric charges accumulated on the screen of television or computer monitor get discharge through our body. Thus, we get a slight shock.
Q 31 – Open a water tap. Adjust the flow so that it forms a thin stream. Charge a refill. Bring it near the water stream. Observe what happens. Write a short report on the activity.
Ans. We observe that water stream is attracted towards the charged refill. It is just like as pieces of papers are attracted by the charged comb. It so happens because water stream and the charged refill have dissimilar charges.
Q 32 – 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 33 – 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 34 – 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 35 – 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 36 – 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 37 – 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 38 – 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.
The strips of an electroscope diverge when a charged body is brought in contact with the metal clip. What will happen to the strips if we gently touch the metal clip with hands?
Ans. The strips will collapse due to discharging of the charges through our hand.
Q 39 – Draw a labelled diagram of a seismograph. Explain its working.
Ans. The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded by an instrument called the seismograph. The instrument is simply a vibrating rod, or a pendulum, which starts vibrating when tremors occur. A pen is attached to the vibrating system. The pen records the seismic waves on a paper which moves under it. By studying these waves, scientists can construct a complete map of the earthquake. They can also estimate its power to cause destruction.
Q 40 – State some precautions that people should take to protect themselves against earthquakes if they live in seismic zones of the country.
Ans. People living in seismic zones should take the following measures for protection against earthquakes:
- All the buildings in these zones should be designed so that they can withstand major tremors. Modern building technology can make it possible.
- In highly seismic areas, the use of mud or timber is better than the heavy construction material. Keep roofs as light as possible. In case the structure falls, the damage will not be heavy.
- It is better if the cupboards and shelves are fixed to the walls, so that they do not fall easily.
- Wall clocks, photo-frames, water heaters etc., should be mounted securely on the walls, so that in the event of an earthquake, they do not fall on people.
- Since some buildings may catch fire due to an earthquake, it is necessary that all buildings, especially tall buildings, have fire fighting equipment in working order