NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

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Some Natural Phenomena NCERT Solutions for Class 8 Science Chapter 15

Class 8 Science Chapter 15 Some Natural Phenomena Exercise Questions and Answers

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:
A crackling sound is heard while taking off a sweater made of synthetic fibre during winters because an electric discharge takes place between the body and the sweater. At the time of electric discharge, some energy is released. In this case, energy is released in the form of a crackling sound.

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 power of an earthquake is expressed in terms of its magnitude on a scale called the Richter scale.
Yes, it would be recorded by a seismograph. But 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:
We have seen that two balloons with similar charges on them, whether positive or negative, repel each other. Similarly, two balloons with dissimilar charges on them attract each other. So, similar charges repel each other while dissimilar charges attract each other.

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 are hung.

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

1. Kashmir
2. Rajasthan
3. Gujarat.

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:
Open vehicles, like motorbike, tractor, construction machinery, open cars are not safe. Open fields, tall trees in woods or isolated ones, shelters in a park, elevated places also do not protect from a lightning strike. Carrying an umbrella is not a good idea at all during a thunderstorm. If in a forest, take shelter under shorter trees.

If no shelter is available, you are in an open field; stay far away from a tall tree. Stay away from poles or other metal objects. Do not lie on the ground. Instead, squat low to the ground. Place your hands on your knees with your head between the hands. This position will make you the smallest target.

Class 8 Science Chapter 15 Some Natural Phenomena 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 Rubbed	Materials Used for Rubbing	Attracts/does not Attract Pieces of Paper	Charged Not  charged
Refill	Polythene, woolen cloth	Attracts	Charged
Balloon	Polythene, woolen cloth, dry hair	Attracts	Charged
Eraser	Wool	Attracts	Charged
Steel spoon	Polythene, woolen cloth	Attracts	Charged
coin	Woolen cloth	Attracts	Charged
Ballpen	Hair	Attracts	Charged

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.