An electroscope is a device which is used to find if an object is:
(c) Free of cracks
Electric current is to be passed from one body to another. For this purpose the two bodies must be joined by:
(a) Cotton thread
(b) Plastic string
(c) Copper wire
(d) Rubber band
The movement of the earth’s plates causes:
Two charged objects are brought close to each other. Choose the most appropriate statement from the following options:
(a) They may attract
(b) They may repel
(c) They may attract or repel depending on the type of charges they carry
(d) There will be no effect
Which of the following is not likely to cause Tsunami?
(a) A major nuclear explosion under sea
(c) Volcanic eruption
The earth’s plate responsible for causing earthquakes is:
(a) The crust of the earth
(b) The mantle of the earth
(c) The inner core of the earth
(d) The outer core of the earth
Consider the list of terms given below:
(i) Seismic Zone
(ii) Fault Zone
(iv) Inner Core
The boundaries of the earth’s plate are known as:
(a) (i) & (ii)
(b) (i) & (iii)
(c) (iii) & (iv)
(d) (ii), (iii) & (iv)
The outermost layer of earth is called:
(b) Outer core
(d) Inner core
Major earthquakes are less likely to occur in:
(a) North East India
(c) Rann of Kutch
Consider the list of terms given below:
Earthquakes can cause:
(a) (i), (ii) & (iii)
(b) (ii) & (iv)
(c) (ii), (iii) & (iv)
(d) (iii) & (iv)
VERY SHORT ANSWER QUESTIONS (5)
State whether the following are True or False.
(a) Earthquakes occur all the time all over the world.
(b) The plates of the outermost layer of the earth are always in continuous motion.
(c) Tremors on the earth can also be caused by the eruption of a volcano.
(d) The process of electric discharge cannot occur between clouds and the earth.
(e) Bathing outdoors should be avoided during thunderstorm.
Is it possible to predict the occurrence of an earthquake?
No. It is not possible to predict the occurrence of an earthquake.
If a charged plastic straw is brought near another uncharged plastic straw, what will happen?
If a charged plastic straw is brought near another uncharged plastic straw, charged plastic straw will attract the uncharged one.
The aluminium strips in an electroscope as shown in the figure below are replaced by plastic strips and a charged body is brought in contact with the metal clip. What will happen?
The strips will not repel each other.
Plastic straws A and B are rubbed with dry cotton cloth. What will happen if they are brought near each other?
When plastic straws are rubbed with dry cotton cloth, they acquire similar charge. So, they repel each other.
SHORT ANSWER QUESTIONS (8)
During the construction of a building the lightning conductor was left hanging in the air by mistake. Would the lightning conductor be still effective? Explain.
A lightning conductor will work even when it is left hanging in the air. The lightning conductor has a sharp tip, through which current flows to the ground. Thus, even when it is hanging in the air, the sharp tip will be there above the building and hence be able to arrest lightning.
If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.
No, lightning would not have occurred. If cloud was a good conductor, it would not have stored charges and would have transferred all charges through air, therefore, lightning would not have taken place.
Identify the lightning conductor and the copper plate in the image below:
A - Lightning conductor
B - Copper plate
If the materials used for constructing a building were good conductors, do you think lightning will strike the building. Will the lightning conductor be still required to be installed in the building?
If the materials used for constructing a building were good conductors, all the work of a lightening conductor would have been done by the conducting material itself. Hence there would have been no need to install lightning conductor in the building.
You might have observed on a dry day that when you touch the screen of a television or computer monitor (with picture tube), you get a slight shock. Why does it happen?
The screen of the television gets electric charge accumulated on it. When we touch the screen, the accumulated charge gets discharged through our body. Thus, we get a slight shock.
Explain how does lightning conductor protects a building from getting struck by lightning.
Lightning conductor conducts the charge to the earth and does not allow the charge to accumulate on a building. Thus, it protects a building from being struck by lightning.
In an electroscope if a negatively charged body is brought in contact with the metal clip, the strips of the electroscope diverge. If now another charged object carrying equal amount of positive charge is brought in contact with the clip, what will happen?
The negative charge of the body will be neutralised if we brought another object carrying equal amount of positive charge in contact with it. As a result, the strips of the electroscope will collapse.
The strips of an electroscope diverge when a charged body is brought in contact with the metal clip. Now the clip is touched gently by our hand. What will happen to the strips? Explain.
As soon as we touch the clip by our hand, the charge present in the electroscope strips will get discharged and the strips will be back to their original state.
LONG ANSWER QUESTIONS (5)
Explain how lightning takes place?
Lightening is a spark that moves within a cloud, between clouds or between the cloud and the ground. It is produced during thunderstorm. During the development of a thunderstorm, air currents in the cloud move upwards and water droplets move downwards. The vigorous movement of air currents cause separation of charges. Due to the separation of charges, positive charges move up and negative charges move down. When two clouds carrying opposite charges approach each other, a large quantity of electric charge flows rapidly from one cloud to the other cloud through the air. This produces lightning.
Mention three precautions that you will take to protect yourself if earthquake strikes when you are inside the house.
The following precautions can be taken when an earthquake strikes:
(i) We should quickly move under the table, bed or desk and stay there until the shaking stops.
(ii) We should so stay away from tall and heavy objects as they may fall on us.
(iii) We should not use lifts as we might get stuck inside.
Explain why it is safer to use a wireless telephone instead of a landline telephone during lightning.
Landline telephone may become dangerous during lightening because atmospheric electric charge may discharge through landline telephone cords. Sometimes, it may even lead to death. So, it is safer to use wireless telephones that cannot carry the lightning discharge.
What precautions would you take if lightning occurs while you are outside the house?
If lightning occurs while one is outside the house, the following precautions can be taken:
· Move to an open space.
· Stay away from poles or other metallic objects.
· Stay away from tall trees and take shelter under short trees.
· Stay away from open vehicles, like motorbikes, cars, tractors, construction machinery, etc.
· Do not lie on the ground. Instead, squat low on the ground.
If the metal clip used in the electroscope is replaced by an ebonite rod and a charged body is brought in contact with it, will there be any effect on the aluminium strips? Explain.
There will not be any effect on the aluminium strips because the ebonite rod is an insulator and the charged body will fail to transfer any charge to the ebonite rod. As a result, there will be no charge on the aluminium strips.