# Electric charge and electric field questions and answers

This page contains electric charge and field important questions along with their answers. This chapter comes under unit Electrostatics. These are the basic set of questions you must do in order to get good understanding of the subject and get good marks.

## Physics class 12 chapter 1 important questions

### Electric Charge

One Marks Questions

Question 1. How will the radius of a flexible ring change if it is given positive charge?

Answer : Increases due to repulsion

Question 2. A positively charged glass rod attracts a suspended ball of straw. Can we conclude that the ball is negatively charged?

Answer Yes, because unlike charges attract each other. When a positively charges glass rod attract a ball of straw this means that ball is negatively charged.

Question 3. How many protons will have the total charge of 1C.

Answer Solve using $q=ne$ and answer is $6.242\times 10^{18}$ protons

Question 4 Does the electric charge vary with the motion of the charged bodies as is the case with mass?

Answer No. The charge on an electron is always $-1.6\times 10^{-19}C$ irrespective of its speed.

Question 5 Give one example of conservation of charge.

Answer Opposite charges appear on two bodies that are being rubbed against each other. For example, when a glass rod is rubbed with a silk cloth, electrons are transferred from glass rod to silk cloth. The glass rod becomes positively charged and the silk cloth becomes negatively charged as it receives extra electrons from the glass rod. Here no charge is being created or destroyed. The net charge is still zero.

Question 6 Out of three charged bodies A,B and C, if A and B repel each other and B attracts C, then what is nature of force between A and C?

Answer A and B repel each other this means they both has same charge. Now B and C attract this means both B and C have opposite charge on them. There would be a force of attraction between A and C as both carries opposite charge.

Question 7 Does charge affect mass of a body?

Answer Yes, very slightly. During charging either a body loose electrons or gain electrons. This transfer of electrons does not bring observable changes in the mass of the body. This is because the mass of electron is very small as compared to the charged body under consideration.

Question 8 Vehicles carrying inflammable usually have metallic ropes touching the ground during motion. Why?

Question 9 What happens when an excess charge is placed on the surface of a conducting body?

Three Marks Questions

Question 1 Explain electrostatic shielding ? Give one example.

Question 2 The earth is receiving 9 protons, 9 positrons per minute per $cm^2$ of its area.?

1 amp = coulomb of charge per second

$Current = \frac{\text{Total charge}}{\text{time in seconds}}$

Charge of a proton $= 1.6 \times 10^{-19} C$

Charge of a positron $= 1.6 \times 10^{-19} C$

Total charge $= 18 \times 1.6 \times 10^{-19} = 2.88 \times 10^{-18} C$

1 minute = 60 seconds

Current $= \frac{2.88 \times 10^{-18}}{ 60} = 4.8 \times 10^{-20} amp$

This is the amount of current which is $1 cm^ 2$ is receiving.

Surface area of sphere $= 4 \pi r^2$

Surface area of the earth$= 4 \pi (6.4 \times 10^6)^2 = \pi \times 1.6384 \times 10^14 m^2$

$1 m = 100 cm\, 1 m^2 = 1 \times 10^4 cm^2$

Surface area of the earth in $cm^2 = \pi \times 1.6384 \times 10^{18}$

Total current $= 4.8 \times 10^{-20}\, amp/cm^2\, \times \pi \times 1.6384\times 10^{18} cm^2$

Total current $= \pi \times 7.86432 \times 10^{-2}$

The total current is approximately 0.247 amp