NCERT Solutions for Class 8 Science Chapter 15 Some Natural Phenomena

In an earlier chapter, students learnt about friction. Now, they learn how friction produces charge and the types of charges and the rules of charge. This is important to understand the natural phenomena of lightning and how it occurs.

This chapter of NCERT solutions for class 8 science will expose students to the two natural phenomena that happen in the sky and on earth. They will learn in detail about why and how lightning and earthquakes occur.

✍ Download PDF of Class 8 Science Chapter 15 Solutiond



Question 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

Solution

(b) A copper rod

Friction can charge the non-conducting materials. Copper conducts electricity easily, so it cannot be charged easily by friction.


Question 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.

Solution

(b) The rod becomes positively charged, while the cloth has a negative charge.

Rubbing is a kind of friction that take place when objects are rubbed against each other. The charge acquire by the glass rod is positive and the charge acquired by the silk cloth is negative in nature.


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

(a) Like charges attract each other. (T / F)
(b) A charged glass rod attracts a charged plastic straw. (T / F)
(c) Lightning conductor cannot protect a building from lightning. (T/F)
(d) Earthquakes can be predicted in advance. (T / F)

Solution

(a) False

Like charges always repel each other.

(b) True. Plastic straw has surplus of electrons so it is negatively charged whereas the glass rod has deficiency of electrons so it is positively charged. So the glass rod will be attracted by the plastic straw.
(c) False. A lightning conductor all the electric charge to pass into the ground. Thus the extra charge that strikes the conductor gets transferred to the ground.
(d) False. Earthquake cannot be predicted in advance. No such device is available till now.


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

Solution:

During the removal of the sweater it is rubbed against our body and the sweater gets charged. Due to this the crackling sound is heard.


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

Water is present in our body in very large amount. When we touch the charged body with our hand. The charged particles move through our body to the ground and we get a shock.

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?


Solution:
Richter scale is used to measure the destructive energy of the earthquake. This scale has readings from 1 to 10. The reading would be recorded by the seismograph.

There will not be any severe damage. An earthquake of more than 5 is considered to be destructive.

Also get access to

NCERT Solutions for Class 8 Maths

Class 8 Maths Worksheets

Class 8 Maths Notes

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

Solution:

Some of the protective measures are given as follows:

We should keep ourselves away from electric poles, metal pipes, and overhead electrical wires.
We should not be in contact of running water.
We should keep ourselves in a completely closed place and remain seated there until the lightning is over.


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

Solution: Same types of charges always repel each other whereas different types of charges attract each other. The surface of the two balloons has the same type of charges, so they repel each other.

The uncharged balloons, when brought near each other, produce a charge on the other uncharged balloon but the nature of the charge is the opposite. Thus, two uncharged balloons attract each other.


Question 9: Describe with the help of a diagram an instrument that can be used to detect a charged body.
Solution:
An electroscope is used to detect the charge on a body.



The electroscope consists of a metal rod, aluminium foil, a metal disc. The aluminium foil is fixed to the end which is inside the flask. When a charged body is touched to the metal disc the aluminium strips move away from each other. This happens as the same kind of charge is transferred to the aluminium strip via the metal rod and we know similar charges repel each other. So this is the reason why two strips moves away from each other.

If an uncharged body is touched to the metal disc, then the strips of the aluminium foil will not move. They will remain as they were before.


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

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


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

Solution
The precautions that can be taken during an earthquake are as follows:

Try to stay away from buildings, electric poles, and trees.
Try to find an open place like a park or playground and stay there till the earthquake passes.


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.

Solution:
In a thunderstorm lightning takes place. The umbrella consists of a metallic rod that can pass the electric charge through it. This gives an electric shock to the person holding it. Thus, it is not safe to carry an umbrella during lightning.

Links to Other Resources for Class 8 Science

Other Class 8 Science Related Links
Understanding Structure and Functions of a Cell
Deforestation, Afforestation and Reforestation
Frictional Force Definition, and Types with Example
Compare LPG and Wood as Fuel
Water Pollution Causes and Effects with Example