Class 8 Science NCERT Solutions for Chapter – 15 Some Natural Phenomena

Some Natural Phenomena

Question 1.
Which of the following cannot be changed easily by friction?

(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woolen cloth

Answer:
(b) A copper rod

Question 2.
When a glass rod is rubbed with a piece of silk cloth the rod

(a) and the cloth both acquire a positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire a negative charge.
(d) becomes negatively charged while the cloth has a positive charge.

Answer:
(b) becomes positively charged while the cloth has a negative charge.

Question 3.
Write T against true and F against false in the following statements.

(a) Like charges attract each other.
Answer:
False

(b) A charged glass rod attracts a charged plastic straw.
Answer:
True

(c) Lightning conductor cannot protect a building from lightning.
Answer:
False

(d) Earthquakes can be predicted in advance.
Answer:
False

Question 4.
Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.

Answer:
The crackling sound is heard because when the sweater is rubbed while taking it off, it acquires a small charge.

Question 5.
Explain why a charged body loses its charge if we touch it with our hand.

Answer:
Our body is a conductor of electricity. When we touch a charged body with our hand, the charged body loses charge to the earth through our body.

Question 6.
Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a Seismograph? Is it likely to cause much damage?

Answer:
The destructive energy of an earthquake is measured on a scale called the Richter scale. An earthquake that measures 3 on the Richter scale Will be recorded by a seismograph. However, it is not likely to cause much damage.

Question 7.
Suggest three measures to protect ourselves from lightning.

Answer:
(1) We should rush to a safer place like a house or building.

(2) If no proper shelter is available and we are in an open field then he/she should stay away from trees, poles, and other metal objects. We should not lie on the ground, instead, we should squat low on the ground i.e., a position where hands are put on knees with head between the hands.

(3) If we are inside the house, contact with telephone cords, electrical wires, and metal pipes should be avoided. Bathing should also be avoided to avoid contact with running water. Electrical appliances like computers, TVs, etc. should be unplugged.

Question 8.
Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

Answer:
A charged balloon is repelled by another charged balloon because both have the same charge. And we know similar charges repel each other. But a charged balloon attracts an uncharged balloon and lose its own charge to the other balloon.

Question 9.
Describe with the help of a diagram an instrument that can be used to detect a charged body.

Answer:
A device that is used to test whether an object is carrying a charge or not is known as an electroscope. A simple electroscope consists of a wide-mouthed bottle over which cardboard, slightly bigger in size than the mouth of the bottle, is placed. A hole is pierced in it. A metallic wire is inserted into the bottle through this hole. On which two strips of aluminum foil about 4 cm × 1 cm each is hung.
NCERT Solutions for Class 8 Science img 39

Question 10.
List three states in India where earthquakes are more likely to strike.

Answer:
The states that fall in seismic zones are more earthquake-prone. Jammu and Kashmir, Himachal Pradesh, and Gujarat are a few such states.

Question 11.
Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?

Answer:
If I am outside my home and an earthquake strikes :

  1. First I will find a clear spot, away from buildings, trees, and overhead power lines.
  2. If I am in a car or a bus, I will not come out. Instead, I will tell the driver to drive slowly to a clear spot and will not come out till the tremors stop.

Question 12.
The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.

Answer:
No, I would not carry an umbrella. Because the pointed rod of the umbrella can become a target of lightning.

InText Questions and Answers

15.2 Charging by Rubbing

Activity 5.2

Question 1.
Record your findings. You can add more items to the table.

Answer:

Objects RubbedMaterials Used for RubbingAttracts/does not Attract Pieces of PaperCharged Not  charged
RefillPolythene, woolen clothAttractsCharged
BalloonPolythene, woolen cloth, dry hairAttractsCharged
EraserWoolAttractsCharged
Steel spoonPolythene, woolen clothAttractsCharged
coinWoolen clothAttractsCharged
BallpenHairAttractsCharged

15.3 Types of Charges and their Interaction

Activity 15.3

Question 1.
What do you observe?

Answer:
Balloons repel each other.

Question 2.
Is there any effect on the refill in the tumbler? Do the two attract each other, or repel each other?

Answer:
Yes. They repel each other.

Question 3.
What happens if two charged objects made of different materials are brought close to each other?

Answer:
They attract each other.

Question 4.
Does it indicate that the charge on the balloon is of a different kind from the charge on the refill?

Answer:
Yes. The charges on the balloon and refill are different.

Question 5.
Can we say then, that there are two kinds of charges?

Answer:
Yes, there are two kinds of charges positive and negative.

Question 6.
Can we also say that the charges of the same kind repel each other, while charges of different kinds attract each other?

Answer:
Yes. It’s true.

Question 7.
What do you think would be the kind of charge on the plastic straw?

Answer:
Plastic straw would carry a negative charge.

15.4 Transfer of Charge

Activity 15.4

Question 1.
Observe what happens. Is there any effect on the foil strips?

Answer:
Yes. The strips become wide open.

Question 2.
Do foil strips behave in the same way in all cases?

Answer:
Yes.

Question 3.
Can this apparatus be used to detect whether a body is charged or not?

Answer:
Yes, it can be. Such a device is known as an electroscope.

Question 4.
Can you explain why the foil strip repel each other?

Answer:
The two paper strips acquire the same charges and that is why they repel each other.

Activity 15.5

Question 1.
Prepare a short report on the suffering of the people during and after the earthquakes.

Answer:
An earthquake is a sudden shaking or trembling of the earth. It is one of the most dreaded natural calamities. During an earthquake, the earth begins to tremble at once. This may result in immense damage to buildings, roads, bridges, dams, etc.

If the magnitude of an earthquake is high, it can cause a great loss of life and property. The area may get completely devastated and can even cause floods, landslides, and tsunamis,

Question 1.
What is an earthquake?

Answer:
An earthquake is a sudden shaking or trembling of the earth lasting for a very short time.

Question 2.
What happens when an earthquake occurs?

Answer:
The earthquake causes immense damage to buildings, bridges, dams, and people. There can be a great loss of life and property. An earthquake can cause floods, landslides, and tsunamis. Thousands of people may lose their lives.

Question 3.
What can we do to minimize its effects?

Answer:
To minimize its effect, it is advisable to make any construction simple so that it is ‘Quake Safe’. We should also take necessary precautions to protect ourselves from earth-quake when we are at home or outdoors.

Activity 15.6

Question 1.
Collect accounts of the devastation caused by the tsunami in India from your parents, or other elders in the family or in the neighborhood.

Answer:
A major tsunami occurred in the Indian Ocean on 26 December 2004, which affected India’s southeast coast, predominantly in the state of Tamil Nadu, as well as the territories of Andaman and Nicobar Islands.

Thousands of people died, and the coastal areas devastated completely. Many fishing communities were ruined by the tsunami, most notably the fishing town of Nagapattinam. Truly, it was one of the worst natural calamities, people have ever witnessed.

Question 4.
My grandmother told me that the earth is balanced on the horn of a bull and when the bull shifts it to the other horn, an earthquake takes place. How could it be true?

Answer:
This is false. In ancient times, people did not know the true cause of earthquakes. Their ideas were, therefore, expressed in mythical stories.

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