# CLASS 8 SCIENCE CHAPTER-15 SOME NATURAL PHENOMENA

Question 1. Identify the one which does not charge by friction that easily?
(i) An inflamed balloon
(ii) A woolen cloth
(iii) A plastic scale
(iv) A copper rod
Solution : (iv) Copper rod
The materials which are non-conducting in nature can be charged by friction easily. Copper which is a highly conducting material cannot be charged that easily.

Question 2. When a silk cloth is rubbed with a glass rod, the rod
(i) and the cloth acquires positive charge.
(ii)and the cloth acquires negative charge.
(iii)becomes positively charged while the cloth is negative charged.
(iv)becomes negatively charged while the cloth is positively charged.
Solution : (iii) the rod becomes positively charged while the cloth is negatively charged.
When two objects are rubbed against each other, they acquire opposite charges. By the law of convention it is known that the rod acquires the positive charge and the cloth is acquires the negative charge

Question 3. State whether the following statement is true or false.
(i) Like charges attract each other.
(ii)A charged glass rod attracts a charged plastic straw.
(iii)The Building cannot be protected from lighting by lighting conductor.
(iv)Prediction of earthquakes can be done in advance.
Solution :
(i)False
Unlike charges attract each other while the like charges repel each other.
(ii) True
A charged plastic straw has a negative charge on its surface while the glass rod has positive charges on its surface. Unlike charges attract each other so, they both attract each other.
(iii) False
When lighting occurs, the atmospheric charges are transferred to the earth directly by lightning conductor. Therefore the building is protected from lighting.
(iv)False
Even though the earthquake causes are known, there is no instruments that is invented to detect them in advance. Therefore earthquakes cannot be predicted in advance.

Question 4. Sometime, a crackling sound is heard while taking off a sweater during winters. Explain.
Solution : The cracking sound is heard because when the sweater is rubbed while taking it off, it acquires a small charge.

Question 5. Explain why a charged body loses its charge if we touch it with our hand.
Solution : Our body is a conductor of electricity. When we touch a charged body with our hand, the charged body loses charge to the earth through our body.

Question 6. Name the scale on which the destructive energy of earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by seismograph? Is it likely to cause much damage?
Solution : The destructive energy of an earthquake is measured on a scale called Richter scale. An earthquake measure 3 on this scale will be recorded by a seismograph. Whoever, it is not likely to cause much damage.

Question 7. Suggest three measures to protect ourselves from lightening.
Solution :
(a) Hearing thunder, we should rush to a safer place like hours or building.
(b) If no proper shelter is available we and in open, never hide under a tree of electric pole.
(c) The telephone cord, electric wires and metal pipes should be avoided from touching.

Question 8. Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?In first case, a charged balloon repels another charged balloon as both have like charges and like charges repel each other.
Solution : In second condition, an uncharged balloon gets attracted towards a charged balloon because the charged balloon induces opposite charge on it. This process of inducing charge on an uncharged body by bringing it close to a charged body is known as induction.

Question 9. Describe with the help of a diagram an instrument which can be used to detect a charged body.
Solution : A device that is used to test whether an object is carrying charge or not is known as electroscope.

Question 10.  List three states in India where earthquakes are more likely to strike.
Solution : The three states in India where earthquakes are more likely to strike are Gujarat, Jammu & Kashmir and Assam.

Question 11. Suppose you are outside your home and an earthquake strikes. What precaution would you take to protect yourself?
Solution : Some precautions which can be taken when someone is outside and an earthquake strikes are:
(i) Try to find clear spot, away from buildings, trees and overhead power lines. Drop to the ground.
(ii) If travelling in a car or a bus, do not come out. Ask the driver to drive slowly to a clear spot and do not come out till the tremors stop.

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 : No, I would not carry an umbrella with me if there is a prediction about a thunderstorm. The reason is, an umbrella has a metallic rod, which serves as a good conductor for lightning to reach human body thereby causing him an electric shock. Hence, we should not carry an umbrella during lightning.

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