NCERT Exemplar Solution Class 8 Science Chapter 15

NCERT Exemplar Solution Class 8 Science Chapter 15

NCERT Exemplar Solution Class 8 Science Chapter 15 Some Natural phenomena all Questions Answer Solution. NCERT Exemplar Class 8 Science Chapter 15 Solution PDF.

NCERT Exemplar Solution Class 8 Science Chapter 15: Overview

NCERT Exemplar Solution Class 8 Science Chapter 15

Board

NCERT

Topic

Exemplar Problem Solution
Class

8

Subject

Science
Chapter

15

Chapter Name

Some Natural phenomena

NCERT Exemplar Solution Class 8 Science Chapter 15 Some Natural phenomena

Multiple Choice Questions

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

a) Charged

b) Magnetic

c) Free of cracks

d) Hot

Answer:- a) Charged

Electroscope is an device which is used to find out whether the object is carrying the charge or not.

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

b) Plastic string

c) Copper wire

d) Rubber band

Answer:- c) Copper wire

Because electrical charges can transferred from one charged body to another charged body through metal conductor. Thus these two bodies must be joined by a metal i.e copper wire.

3) The movement of the earth’s plates causes

a) Cyclones

b) Lightning

c) Earthquakes

d) Thunderstorms

Answer:- c) Earthquakes

Cyclones, lightning, and thunderstorms are also natural phenomena but these does not occurs due to the movement of earth’s plates. Earthquakes causes due to the movement of the earth plates in the crust.

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 changes they carry

d) There will be no effect.

Answer:- c) They may attract or repel depending on the type of changes they carry.

Like charges repel each other and the unlike charges attract each other. These are dependent over the charges they carry are same or not.

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:- d) Lightning

Tsunami is a natural phenomena which occurs in the sea. These occurs when there is Earthquakes, volcanic eruption, or nuclear explosion under the sea. But lightning atmosphere is not responsible for the tsunami.

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:- a) the crust of the earth.

Earthquake caused when there is disturbance occurs deep inside earth’s crust.

7) Consider the list of terms given below:

a) Seismic zone

b) Fault zone

c) Mantle

d) Inner core

The boundaries of the earth’s plate are known as

a) I and II

b) I and III

c) III and IV

d)II, III, and IV

Answer:- a) I and II

The boundaries of the earth plate are known as seismic zone and fault zone. These are the plates where Earthquakes occurs as these are weak zones.

8) The outermost layer of the earth is called

a) Mantle

b) Outer core

c) Crust

d) Inner core

Answer:- c) Crust

Crust is the outermost layer of the earth. These crust is not in the single piece. These is divided into fragments. These fragments are known as plates. Mantle, outer core, and inner core are present below the crust respectively.

9) Major earthquakes are less likely to occur in

a) North East India

b) Rajasthan

c) Rann of Kutch

d) Orissa

Answer:- d) Orissa

The fault  or seismic zone  are the weak zones where the earthquake occurs more times. These zones are not present near the Orissa. And thus there are less likely to occur major earthquakes.

10) Consider the list of terms given below.

a) Tsunami

b) Landslide

c) Floods

d) Lightning

Earthquakes can cause

a) I, II, and III

b) II and IV

c) II, III, and IV

d) III and IV

Answer:- a) I, II and III

Earthquakes occurs due to the movement of the earth plate in the curst. These is responsible for the tsunami, landslide and floods over the earth surface. But lightning in sky is not occur due to earthquake.

Very Short Answer Questions

11) State whether the following are True or False.

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

Answer:-  True

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

Answer:- True

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

Answer:- True

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

Answer:- False

The process of Electric discharge can occur between the clouds and the earth. Which is known as lightning.

e) Bathing outdoors should be avoided during thunderstorm.

Answer:- True

12) Is it possible to predict the occurrence of an earthquake?

Answer:- No. Earthquake is the natural phenomena, which cannot be yet predict accurately.

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

Answer:- When a charged Plastic straw is brought near another uncharged plastic straw they both will attract each other. Because both the charges are different and unlike charges attract each other.

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?

Fig. 15.1

Answer:-

Electroscope is the device which is used to find out whether the object is carrying charges or not. If the aluminium strip is replaced with the plastic then the strips will not show diversion. As plastic is bad Conductor of Electricity. It will bot show any diversion.

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

Answer:- Same charges repel each other and like charges attract each other. Here both the charges are same, rubbing of plastic straws with the cotton cloth will generate same  Electric charge in it. And thus these charges will repel each when they are brought together.

Short Answer Questions

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:- No. If it is hanged in air then it will not be effective. Earthing is the process in which the transfer of charges takes place through the charged body to the earth. But here the lightning conductor is left in the air and was not connected to the earth properly, thus the charge will not pass into the earth.

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

Answer:- No. Lightning would not occur in these case . Lightning takes place when there is collision of separated positive and negative charges over each. These charges could not be separated in the good Conductors. Thus in good Conductors charges will not be accumulated on clouds and if there is not accumulation of charges then there will not be Lightning.

18) Identify the lightning conductor and the copper plate in fig. 15.2

Fig. 15.2

Answer:-

A is showing the lightning conductor and

B is showing the copper plate.

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. lightning conductor dose not allow Electric charges to accumulate over the  building. lightning Conductor provide the path for transferring electric charge to the earth.  thus lightning conductor will not be required to installed in the building, if material is good conductor as it will provide the path for the Electric charge.

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:- We get a minute shock on the dry day, while touching screen of television, because the Electric charges get accumulated over the screen. as soon as we  touch the screen these charges discharge through our body. And we get  small shock.

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

Answer:- Lightning Conductor provide a suitable path for the Electric charges to transfer it to the earth. These process is also known as earthing. These lightning Conductor does not allow the charges to accumulate over the building. And thus it protects a building from getting stuck.

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:-  When the electroscope is charged with the negative charges it shows the diversion, but as soon as the equal amount of Positive charge is brought in contact with the strips then the electroscope will be neutralised by Positive and negative charges cancellation. And thus the strips which were diverse will collapse.

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:- When a charge body is brought in contact with metal clip and  the metal clip is touched by hands, then the charges over the metal clip will be discharged through our hand, due to these we can feel a minute shock and the diverged electroscope strips will be back into their original position.

Long Answer Questions

24) Explain how lightning takes place?

Answer:-  When there is thunderstorm, the current of air moves up and droplets of water move towards down. These tremendous movement of air causes the separation of the charges. Due to these process, which is yet not completely understand, the negative charges accumulated on the lower edge of the clouds while the positive charges accumulated over the upper edge of the clouds. Also the positive charges started accumulation on the ground. Normally the air is poor conductor of Electricity , when there is large amount of charges accumulated that the it will able to resist the flow. Then positive and negative charges comes in contact and produces streaks of light and tremendous sound. And these streaks are seen as Lightning. And these lightning process is also known as electric discharge.

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

Answer:- The precaution to be taken while earthquake sticks and you are inside the house are as below-

1) If you are at home then go below the table or bed and take shelter of below it up to the shaking stops.

2) Important thing is to protect your head by any material.

3) Keep distance from the heavy objects and tall pillars etc.

4) If you are outside the home then  get away from the buildings, electric power pillars, and tall trees.

5) Stay on the clear ground.

6) If you are travelling in the car or bus then do not come out of it and drive slowly to the

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

Answer:-It is not safe to use landline telephones during the lightning. Because lightning is the electrical discharged. From these lightning, electric discharged may occur through the landline’s wires and this can be dangerous for the human near it during the lightning Weather.

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

Answer:- The following precautions must be taken while lightning occurs and you are outside the house-

1) Keep distance from the trees, do not stand below any tree.

2) Keep distance from the electric poles and any other metallic objects.

3) Do not go close to the motorcycles , construction machinery , and tractors. These are not safe.

4) If you are standing in open place then squat low on the ground and keep your hands on the knees and put headbetween the hands. Stay in these position while lightning.

5) Search a safe place when there is thunder and lightning.

6) Contact with the telephone, television should be avoided.

7) All the electrical devices should be unplugged. But lights can be keep on.

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:- Metal conductor carries the charges from one charged body to the another body. But ebonite rod is an insulator therefore the charged body cannot transfer any charges to the ebonite rod. Therefore charge will not be reach to the aluminium strips and thus there will not be any repulsion by the strips.

Updated: April 28, 2021 — 2:18 pm

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