NCERT Class VIII Science Solutions: Chapter 15-Some Natural Phenomena Part 4

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Question 19:

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?

Answer:

No. There is no need to install lightning conductor in the building.

Question 20:

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?

Answer:

Electric charge gets accumulated on the screen. On touching the screen the charge discharges through our body. Thus, we get a slight shock.

Question 21:

Explain how does lightning conductor protects a building from getting struck by lightning.

Answer:

Lightning conductor does not allow the charge to accumulate on a building as it conducts the charge to the earth, protecting building from being struck by lightning.

Image of how to protect your building by lighting conductor

Image of How to Protect Your Building by Lighting Conductor

Image of how to protect your building by lighting conductor

Question 22:

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?

Answer:

If a positively charged object is brought in contact with the clip of an electroscope, the negative charge given earlier will be neutralised and the strips will collapse.

Question 23:

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.

Answer:

The charge that was in the electroscope strips will get discharged through our hand. The strips will come back to the original state.

LONG ANSWER QUESTIONS

Question 24:

Explain how lightning takes place?

Answer:

During the development of a thunderstorm, the air currents move upwards while the water droplets move downwards. These vigorous movements of air currents cause separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitudes of the accumulated charges become large, the air cannot resist their flow. As a result negative and positive charges meet producing a streak of bright light and sound, called lightning.

Question 25:

Mention three precautions that you will take to protect yourself if earthquake strikes when you are inside the house.

Answer:

  1. Take shelter under a table and stay there till the shaking stops.

  2. Stay away from tall and heavy objects that may fall on you.

  3. If you are in bed, do not get up. Protect your head with a pillow.