NCERT Class 8 Science Chapter 15 - Some Natural Phenomena

Chapter 15 - Some Natural Phenomena

Select the correct option in Questions 1 and 2.
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.
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 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.
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 (T/F)
b) A charged glass rod attract 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)
Answer:
a) False
b) True
c) False
d) False

Question 4: Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Answer: When we take off a sweater during winters, sweater gets charged due to friction between the sweater and the body. This makes a crackling sound.

Question 5: Explain why a charged body loses its charge if we touch it with our hand.
Answer: The charges get conducted to the Earth through our body when we touch it and the charged body loses its charge. The process of transferring of charge from a charged object to the earth is called earthing.

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 a magnitude on a scale called the Richter scale. This scale has the reading from 1 to 10. Yes, it would be recorded by seismograph because this scale has the readings from 1 to 10. No, it isn’t likely to cause much damage because the earthquakes having magnitude higher than 5 are considered harmful in nature.

Question 7: Suggest three measures to protect ourselves from lightning.
Answer:
• Electrical appliances like computers, TVs, etc., should be unplugged. Electrical lights can remain on. They do not cause any harm.
• Bathing should be avoided during thunderstorms to avoid contact with running water.
• Stay away from poles or other metal objects. Do not lie on the ground. Instead, squat low on the ground. This position will make you the smallest target to be struck.

Question 8: Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Answer: The charge on the balloons have the same nature (i.e. either positive or negative) so they get repelled. Whereas when a charged balloon is brought near an uncharged balloon due to the induction of charges, it get charges which are opposite in nature with that of a charged balloon. Since, unlike charges attract each other, the uncharged balloon gets attracted by the charged balloon.

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

The aluminium foil strips receive the same charge from the charged refill through the paper clip (since metals are good conductors of electricity). The strips carrying similar charges repel each other and they become wide open. Such a device can be used to test whether an object is carrying charge or not. This device is known as electroscope. Thus, we find that electrical charge can be transferred from a charged object to another through a metal conductor.

Question 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 Gujarat, Assam and Jammu & Kashmir. 

Question 11: Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Answer:
• Move to open space. Find an empty spot away from buildings, trees and overhead power lines.
• If we are in a car or a bus, will not come out. Drive slowly to a clear spot and remain in it till the earthquake stops.

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: No, we shouldn’t carry an umbrella at all because parts of umbrella is made up of metallic objects that may cause electrical shock to the person carrying it. So an umbrella will increase the risk.