Class 8 Science Chapter 12 Question Answers - Some Natural Phenomena

Q1: 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.

Q2: What is static charge? How does it differ from electric current?
Ans: The electric charges generated by rubbing are called static charges. The static charges do not move while charges move in electric current.

Q3: 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.

Q4: 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.

Q5: What is an earthquake? How is it caused?
Ans: Sudden shaking and trembling of the earth is called an earthquake. It is caused mostly due to the movement of the earth's plates inside the crust.

Q6: What is a lightning conductor? Where is it fixed?
Ans: A lightning conductor is a device used to protect buildings from the danger of lightning. It is fixed at the top of the building.

Q7: 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.

Q8: 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.

Q9: What is earthing? What is the application of earthing?
Ans: The process of transfer of charges from a charged object to the earth is called earthing. It is provided in buildings to protect from electrical shocks due to any leakage of electrical current.

Q10: What do you mean by electric discharge? How does it occur?
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.

Q11: 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.

Q12: 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 above 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.

Q13: 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.

Q14: What is a lightning conductor? How does it work?
Ans:
Lightening Conductor

• 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.

Q15: 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.

Q16: 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. below). The outermost layer of the earth is fragmented. Each fragment is called a plate (Fig. below). These plates are in continual motion. When they brush one another, or a plate goes under another due to collision (Fig. below), they cause disturbance in the earth’s crust. It is this disturbance that shows up as an earthquake on the surface of the earth.

Movements of earth's plates