Q.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
Ans.
(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.
Q.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.
Ans.
(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.
Q.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.
Ans.
(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.
Q.4. While taking off the sweater sometimes crackling sound occurs. Explain
Ans.
Due to the friction between the sweater and the body when it is taken off, the woolen sweater gets charged. So, the crackling sound is heard in this process.
Q.5. When we touch a charged body it loses its charge. Explain why?
Ans.
The charges gets conducted to the earth through our body when we touch it and the conductor loses its charge. This phenomenon is known as electric discharge.
Q.6. Destructive energy of an earthquake is measured on what scale? An earthquake measuring 3 on this scale would be recorded by a seismograph?How much damage it is likely to cause?
Ans.
Richter scale is used to measure the destructive energy of an earthquake. The scale has a reading from 1 to 10.
An earthquake measuring 3 would be recorded by a seismograph.
Magnitude of scale 3 would not cause much damage. An Earthquake of magnitude 5 is considered destructive in nature.
Q.7. what are the ways to protect ourselves from lightning?
Ans.
Various ways to protect ourselves from lighting are:
(i) Always remain in a closed place and if you are in a car stay there until the lighting is over and keep the windows closed.
(ii) Never touch any electrical wires, telephone cables, metal pipes.
(iii) Never bath in running water, this may cause electric shock.
Q.8. When two charged balloon come close to each other they repel each other whereas when an uncharged balloon comes close to charged balloon it gets attracted. Why is that?
Ans.
The surface charge on the balloons are of same nature and since like charges attract each other, the two balloons are repelled. When a charged balloon is brought near an uncharged balloon due to the induction of charges, it acquires charges on its surface and these charges are opposite in nature with that of charged balloon. As unlike charges attract each other, the uncharged balloon gets attracted by the charged balloon.
Q.9. Draw an instrument which detects the charged body and describe it.
Ans.
The instrument used to detect the charged body is an electroscope.
It consist of a metal rod on which two leaves of aluminum foil are fixed to one end and a metal disc at the other end. The leaves are kept inside a conical flask and it is corked to isolate it from the atmospheric air.
When a charged body comes in contact with the metal disc, the aluminum leaves move away from each other because some charges gets transferred to aluminum leaves through the metal rod. This process is called charging by conduction. The charges on the leaves and the charged body are of same in nature and thus the leaves of aluminium repel each other. If the body is not charged then they would attract each other.
Q.10. In what three states of India, earthquake are prone to strike.
Ans.
Gujarat, Assam and Jammu & Kashmir are the three states where earthquake are more likely to strike.
Q.11. What precaution would you take to protect yourself when an earthquake occurs and you are outside?
Ans.
The following should be taken
(a) Find and go to an open field and stay away from buildings, trees, electric wire and poles.
(b) If you are in a car, then drive to an open field and do not come out of your car.
Q.12. You are supposed to go out on a particular day and the weather department has forecasted that a thunderstorm is likely to happen. Would you carry an umbrella? Explain.
Ans.
No, one should not carry an umbrella during a thunderstorm. Thunderstorm is accompanied by lighting and the charges might travel from the cloud to the metal rod on the umbrella and might cause electric shock to the person carrying it. So, it is not safe to carry an umbrella during lighting.
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