### Short Question Solution

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#### Kinematics

Introduction to Kinematics

# Electrostatics - Short Question Answers 1

1. Bits of paper are attracted to an electrified comb, even though they have no net charge. How is it possible?
When a comb runs through hair, it gets charged due to friction with hair. This charged comb when brought close to the paper, it induces an opposite charge on paper pieces and attracts to paper even though they have no net charge. If the hair is wet the friction between hair and comb is highly reduced and hence, the comb is less charged. Thus, in this case, it cannot attract paper.

2. What do you mean by quantization of charge? Explain.
The charges on any charged body are an integral multiple of the basic unit of charge. This basic unit of charge is taken as the charge on an electron or a proton which is equal to +- 1.6 * 10-19 C. Therefore, the charge on anybody is, Q = +- n e where e is the charge on an electron and n is any integer. This property of charge is known as quantization of electric charge.

3. We often experience sparks during winter nights while removing the clothes from our bodies. Why?
In winter season, our body is dry but not wet because of which friction is produced while removing clothes and we feel sparks due to it.

4. What is the magnitude of an electric field which will balance the weight of an electron on the surface of the Earth?
Let E be the value of electric field strength of an electron which will just balance its weight on the surface of the earth, then,
Electric force = Weight of an electron
or, eE = W
or, eE = meg
or, E = meg / e
Putting the values of me = 9.1 * 10-31kg, e = 1.6 * 10-19 C and g = 9.8 m/ s2 in the equation, we get
E = 5.68 * 10­-11 N/C

5. What is potential gradient? How is it related with the electric field intensity?
The rate of change of electric potential with respect to distance is called electric potential gradient. It is given as,
It is related with electric field intensity as, E = -dV/dr

6. Why does bodies get electrified when they are rubbed together for a while?
When two bodies are rubbed together for a while, there exists a transfer of electrons from one body to another body due to which one of them loses one electron and becomes positively charged whereas another body gains that electron and becomes negatively charged. So, this is how a body gets electrified when they are rubbed together for a while.

7. A man inside an electric cage does not receive an electric shock when it is highly charged. Why?
The potential at each point inside the cage is same, so the man does not get shock even when the cage is highly charged.

8. Why is it dangerous to sit under a tree when it is lightening?
Green tree is a good conductor of electricity. So, during lightning there is maximum possibility of the tree to be hit by it. So, it is dangerous to sit under a tree when it is lightning.

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