NCERT Solutions of Chapter: Some Natural Phenomena. NCERT Solutions along with worksheets and notes for Class 8.
Select the correct option in Questions 1 and 2.
(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.
Ans- 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 with 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.
Ans- becomes positively charged with 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)
(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)
Ans-
(a) Like charges attract each other (F)
(b) A charged glass rod attract a charged plastic straw (T)
(c)Lightning conductor cannot protect a building from lightning (F)
(d) Earthquakes can be predicted in advance (F)
(4) Sometimes, a crackling sound is heard while taking off a sweater during winters. Explain.
Ans- Our sweater rubs on our shirt continuously. As a result, both, gets charge with opposite charges. When we pull off our sweater the accumulation of opposite charges gets discharge and release light and sound. Therefore, a crackling sound is heard while taking off a sweater during winters.
(5)Explain why a charged body loses its charge if we touch it with our hand.
Ans- Our body is good conductor of electricity. Therefore when we touch the charged body the charge passes to earth. Hence, a charged body loses its charge if we touch it with our hand.
(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?
Ans- The destructive energy of an earthquake is measured on Richter scale.
Yes, it would be measured by a seismograph.
No, it will not be very destructive. The magnitude more than 7 is considered as a destructive earthquake.
(7) Suggest three measures to protect ourselves from lightning.
Ans– Three measures to protect ourselves from lightning are listed below:-
(a) Take shelter under a table and stay there till the shacking stops.
(b) Stay away from tall and heavy objects that may fall on you.
(c) If you are in bed, do not get up. Protect your head with pillow.
(8)Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?
Ans- If objects have like charge (either positive or negative) they will repel each other. If they have unlike charge (one positive and other negative) they will attract each other. Therefore, a charged balloon is repelled by another charged balloon because both have like charge. But an uncharged balloon is attracted by another charged balloon because they have unlike charge.
(9) Describe with the help of a diagram an instrument which can be used to detect a charged body.
Ans- An electroscope is used to detect a charged body.
Instrument
Place a cardboard piece on the mouth of the glass bottle. Pierce a hole in the card board. Take two aluminium foil piece and hang them on the paper clip. Put the aluminum foil sheets in the glass bottle. Rub a ball pen refill with polythene. Now, bring it near to paper clip. Aluminium foil sheet will repel each other. It can happen only because charge of refill transfers to paper sheet and through paper sheet aluminium foil sheet gets charged.
(10) List three state sin India where earthquakes are more likely to strike.
Ans- Kashmir, Gujarat and Rajasthan are the three states in India where earthquakes are more likely to strike.
(11) Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Ans- Precautions taken at the time of earthquake when outside the home are listed below:-
(a) Find a clear spot on the ground away from the buildings, trees and overhead power lines.
(b) Do not come out from a car. Move car slowly and try to reach a safe place.
(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.
Ans-No, I would not carry umbrella on the day when a thunderstorm is predicted. Metal is a good conductor of electricity. Therefore, lightning at the time of thunder can pass to me through metal rod of the umbrella and harm me.
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