class8th Chapter 15 Some Natural Phenomena solutions

NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

Page No: 197

Exercise

1. Which of the following cannot be charged easily by friction?
(a) A plastic scale
(b) A copper rod
(c) An inflated balloon
(d) A woollen cloth
► (b) A copper rod

2. When a glass rod is rubbed with a piece of silk cloth the rod
(a) and the cloth both acquire positive charge.
(b) becomes positively charged while the cloth has a negative charge.
(c) and the cloth both acquire negative charge.
(d) becomes negatively charged while the cloth has a positive charge.
► (b) becomes positively charged while the cloth has a negative charge.

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

(a) Like charges attract each other. (T / F)
► False

(b) A charged glass rod attracts a charged plastic straw. (T / F)
► True

(c) Lightning conductor cannot protect a building from lightning. (T/F)
► False

(d) Earthquakes can be predicted in advance. (T / F)
► False

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

Answer

Sweater is made of wool and generally shirt we wear is made of cotton blended with some synthetic fibers. Constant friction between the shirt and sweeter lets transfer of electrons from one material to the other. This results in building of electric potential. When enough potential has been accumulated, while taking of the sweater it discharges and transfer of electrons take place. Passage of electrons through air in the forms of spark let out heat and sound energy. Thus we hear the crackling sound and in dark rooms we may see the spark lights as well.

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

Answer

When we touch a charged body, with our hand, the excess of accumulated charge or static charges on it, gets transfer to ground through our body. Thus the charged body loses its charge, and becomes neutral.

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 Richter Scale.

The reading of magnitude 3 on the Richter scale would be recorded by a seismograph.
If the Richter scale gives a reading of magnitude 3, then the earthquake is not likely to cause much damage. Generally, earthquake of magnitudes higher than 5 is considered destructive in nature.

7. Suggest three measures to protect ourselves from lightning.

Answer

Protective measures against lightning are:→ Stay indoor or under covered area.
→ Do not take bath during lightning.
→ Do not use any electrical appliances during lightning.

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 carry same charges and we know same charges repel each other whereas an uncharged balloon is attracted by charged balloon because unlike charges attract each other.

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

Answer

An electroscope can be used to detect whether a body is charged or not. The following figure shows a simple electroscope.

In an Electroscope, two metal foils are hanged with the help of a conductor in a glass jar with a lid. When a charged body touches this conductor, its charged gets transferred to the metal foil and they move apart due to like charges. This shows that an electroscope detects charges.

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

Answer

The three states in India where earthquakes are more likely to strike are Jammu and Kashmir,Gujrat, and Assam.

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

Answer

Some of the precautions are:

→ Try to move to an open space.
→ We should not take shelter under trees, buildings or overhead power lines.
→ If travelling in a bus or a car, then do not come out when an earthquake strikes. Ask the driver to drive in an open field.

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. We should not carry an umbrella in a thunderstorm. During thunderstorms, which are accompanied with lightning, electric discharge from the clouds can travel through the metallic rod of the umbrella. This may give an electric shock to the person who is carrying it. Hence, it is not safe to carry an umbrella during lightning.

Go Back To NCERT Solutions for Class 8 Science

Chapter 15 Some Natural Phenomena Class 8 Science NCERT Solutions

Chapter 15 NCERT Questions and Answers can be used to enrich knowledge and make lessons for learners more exciting. These are helpful in building a great foundation of concepts and make easy for the students to understand basics. In the examinations, you will can come up with better answers and lay out the main point effectively.

Class 8 Science Chapter 15 Some Natural Phenomena NCERT Questions and Answers – Topics

• Lightning

→ The Sparks that the Greeks Knew About

• Charging by Rubbing

• Types of Charges and Their Interaction

• The Story of Lightning

• Lightning Safety

→ Finding a Safe Place

→ Do’s and Don’ts during a Thunderstorm

• Earthquakes

→ What is an Earthquake?

→ What Causes an Earthquake?

→ Protection against Earthquakes

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

• Lightning is an electric spark caused by the accumulation of charges in the clouds.

• The electrical charge produced by rubbing is called static charge. There are two kinds of charges—positive charge and negative charge.

→ It is a convention to call the charge acquired by a glass rod when it is rubbed with silk as positive. The other kind of charge is said to be negative.

→ Charges of the same kind repel each other, while charges of different kind attract each other. When charges move, they constitute an electric current.

• Electroscope is a device that can be used to test whether an object is carrying charge or not. Electroscope consists of closely placed two metallic (aluminium) foils or strips. When both the strips are charged with similar charges, they repel each other and become wide open.

• The process of transferring of charge from a charged object to the earth is called earthing.

→ During lightning and thunderstorm no open place is safe.

→ Hearing thunder is an alert to rush to a safer place.

• Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground.

• After hearing the last thunder, wait for some time before coming out of the safe place.

• An earthquake is a sudden shaking or trembling of the earth lasting for a very short time. It is caused by a disturbance deep inside the earth’s crust.

• Earthquakes tend to occur at the boundaries of earth’s plates. These boundaries are known as fault zones.

• Destructive energy of an earthquake is measured on the Richter scale. The earthquake measuring 7 or more on Richter scale can cause severe damage to life and property.

Chapter 15 Some Natural Phenomena Class 8 Science Questions and Answers – MCQ Questions with answers

1. What is the purpose of an electroscope?

a) To detect and test small electric charges

b) To calculate the amount of electric charge flowing through the conductor

c) To find out the presence of antimatter

d) To test the presence of magnetic field

► a) To detect and test small electric charges

2. Earthquakes are caused by the

a) Tilting of earth axis

b) Movement of water inside

c) High pollution level

d) Movement of earth plates

► d) Movement of earth plates

3. The power of earthquake is measured in terms of

a) Fernier scale

b) Richter scale

c) Newton

d) Pascal

► b) Richter scale

4. Lightning occurred when two charges meet they are

a) both positive

b) both negative

c) one positive and other negative

d) none of the above

► c) one positive and other negative

5. Lightening strike could destroy

a) Life and property

b) Animals only

c) Plants only

d) Microbes only

► a) Life and property

6. When we remove polyester or woollen clothes in dark, we can see a spark and hear a crackling sound. Which of the following is responsible for it?

a) Static electricity

b) Current electricity

c) Positive charge

d) Negative charge

► a) Static electricity

7. Earthing is the process of transferring charge from charged object to

a) Opposite charge

b) Water

c) Earth

d) Neutral

► c) Earth

8. When you touch a charged body, the charge flows through you into the earth. What is this called?

a) Induction

b) Conduction

c) Capacitance

d) Earthing

► d) Earthing

9. Why is a lightning conductor installed on a building?

a) So that it collects the electric power present in the lightning

b) So that it repels the lightning that falls on the building

c) So that it forces the lightning to fall in an area where there are no buildings

d) So that it conducts electric charge to the ground when lightning strikes the building

► d) So that it conducts electric charge to the ground when lightning strikes the building

10. Which scientist showed that lightening and sparks from clothes is same phenomenon?

a) Isaac Newton

b) Rutherford

c) Alfred Noble

d) Benjamin Franklin

► d) Benjamin Franklin