Chapter 15: Some Natural Phenomena

                       Science

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                  Chapter 15: Some Natural Phenomena

              Class: VIII

                                               Exemplar Solutions

 

MULTIPLE CHOICE QUESTIONS

Question 1

An electroscope is a device which is used to find if an object is

(a) charged                        (c) free of cracks

(b) magnetic                       (d) hot

Answer 1 (a)

 

Question 2

Electric current is to be passed from one body to another. For this purpose the two bodies must be joined by

(a) cotton thread                 (c) copper wire

 (b) plastic string                 (d) rubber band

Answer 2 (c)

Question 3

The movement of the earth’s plates causes

 (a) cyclones      (c) earthquakes

 (b) lightning                        (d) thunderstorms

Answer 3 (c)

 

Question 4

Two charged objects are brought close to each other. Choose the most appropriate statement from the following options:

(a) they may attract

(b) they may repel

(c) they may attract or repel depending on the type of charges they carry

(d) there will be no effect

Answer 4 (c)

 

Question 5

Which of the following is not likely to cause Tsunami?

(a) A major nuclear explosion under sea

 (b) Earthquake

(c) Volcanic eruption

 (d) Lightning

Answer 5 (d)

 

Question 6

The earth’s plate responsible for causing earthquakes is

(a) the crust of the earth

(b) the mantle of the earth

(c) the inner core of the earth

(d) the outer core of the earth

Answer 6 (a)

 

Question 7

Consider the list of terms given below:

• Seismic Zone (iii) Mantle
• Fault Zone                  (iv) Inner Core

The boundaries of the earth’s plate are known as

(a) (i) & (ii)          (c) (iii) & (iv)

(b) (i) & (iii)         (d) (ii), (iii) & (iv)

Answer 7 (a)

Question 8

The outermost layer of earth is called

(a) mantle           (c) crust

(b) outer core      (d) inner core

Answer 8 (c)

Question 9

 Major earthquakes are less likely to occur in

(a) North East India                           (c) Rann of Kutch

 (b) Rajasthan         (d) Orissa

Answer 9 (d)

Question 10

Consider the list of terms given below

• Tsunami (iii) Floods
• Landslide (iv) Lightning

Earthquakes can cause

(a) (i), (ii) & (iii)         (c) (ii), (iii) & (iv)

(b) (ii) & (iv)              (d) (iii) & (iv)

Answer  10 (a)

VERY SHORT ANSWER QUESTIONS

Question 11

State whether the following are True or False.

(a) Earthquakes occur all the time all over the world.

(b) The plates of the outermost layer of the earth are always in continuous motion.

(c) Tremors on the earth can also be caused by the eruption of a volcano.

(d) The process of electric discharge cannot occur between clouds and the earth.

(e) Bathing outdoors should be avoided during thunderstorm.

Answer 11

(a) True (b) True (c) True (d) False (e) True

Question 12

Is it possible to predict the occurrence of an earthquake?

Answer 12

No

Question 13

If a charged plastic straw is brought near another uncharged plastic straw, what will happen?

Answer 13

The two will attract each other.

Question 14

The aluminium strips in an electroscope as shown in fig. 15.1 are replaced by plastic strips and a charged body is brought in contact with the metal clip. What will happen?

Answer 14

No divergence of strips will take place.

 

Question 15

Plastic straws A and B are rubbed with dry cotton cloth. What will happen if they are brought near each other?

Answer 15

They will repel each other.

SHORT ANSWER QUESTIONS

Question 16

During the construction of a building the lightning conductor was left hanging in the air by mistake. Would the lightning conductor be still effective? Explain.

Answer 16

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.

Question 17

If air and cloud were good conductors of electricity, do you think lightning could occur? Explain.

Answer 17

No, it will not occur. The charge separation cannot take place in conductors. Therefore charges will not accumulate on clouds and so lightning cannot take place.

Question 18

Identify the lightning conductor and the copper plate in Fig. 15.2.

Answer 18

A is the lightning conductor and B is the copper plate.

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 19

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 20

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 21

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.

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 prositive charge is brought in contact with the clip, what will happen?

Answer 22

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 23

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 24

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 magnitude 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 25

• Take shelter under a table and stay there till the shaking stops.
• Stay away from tall and heavy objects that may fall on you.
• If you are in bed, do not get up. Protect your head with a pillow.

 (If a child gives any other reasonable precautions, it should be accepted)

 

Question 26

Explain why it is safer to use a wireless telephone instead of a landline telephone during lightning.

Answer 26

Lightning is an electrical discharge. During lightning atmospheric electric charge may discharge through landline telephone wires and may become dangerous. Therefore it is safer to use a wireless telephone instead of a landline telephone during lightning.

Question 27

What precautions would you take if lightning occurs while you are outside the house?

Answer 27

• Stay away from poles or other metallic objects.
• Stay away from tall trees.
• Stay away from open vehicles like motorbikes, tractors, construction machinery etc. (If a child gives any other reasonable precautions, it should be accepted)

Question 28

 If the metal clip used in the electroscope is replaced by an ebonite rod and a charged body is brought in contact with it, will there be any effect on the aluminium strips? Explain.

Answer 28

The aluminium strips will not show any repulsion. The charged body will not transfer any charge to the ebonite rod as ebonite rod is an insulator. As a result there will be no charge on the aluminium strips and no repulsion will occur.