Class 8 Science Chapter 12 HOTS Questions - Some Natural Phenomena

Q1: 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.

Q2: 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.

Q3: 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.

Q4: 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.

Q5: 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.

Q6: On 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.

Q7: Ms Neena, Science teacher of class VIII, taught children how to protect themselves and what to do during an earthquake. She even performed an earthquake drill in school for better understanding in children. Children enjoyed this drill and learned a lot from this.
(a) What to do during an earthquake if you are stuck indoor?
(b) What causes earthquakes?
(c) How you must keep yourself ready for an earthquake?
(d) What values of Ms Neena is shown here?
Ans: (a) The following must be done if someone had stuck indoor:

• Stay away from glass, windows, outside doors and walls.
• Stay away from anything that could fall such as lightning fixtures or furnitures.
• Get under a sturdy table/desk, hold it firmly and cover your head.
• Stay calm and do not panic. Stay inside until shaking stops and it is safe to go outside.

(b) Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake.
(c) We must keep ourself ready for an earthquake by:

• Having proper knowledge about do’s and don’ts during an earthquake.
• Keeping a disaster kit ready in the time of need.
• Helping needy and injured person after an earthquake.

(d) Ms Neena has future vision, scientific temperament, intelligent, compassionate, caring, dedicated, etc.

Q8: 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.

Q9: 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.

Q10: 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.