Question

On charging a soap bubble, its radius increases. This is because
A. because the charges on the surface of the bubble attract each other
B. because the pressure outside drops
C. because the charges on the surface of the bubble repel each other
D. None of the above

Answer 1

Hint: When the soap bubble is charged with a particular type of charge, the charges will get uniformly distributed over the surface of the soap bubble. When these charges are distributed uniformly, the electrostatic force between the charges starts to play their role and these charges attract each other if they are opposite and repel if they are the same.

Complete step by step answer:
When the bubble is not charged by any charge, the soap bubble holds its size due to the constant surface tension force on it.
But when the soap bubble is charged with a charge (may be positive or negative), these charges start to get uniformly spread over the surface of the soap bubble.
Since all the charges have the same charge (positive or negative), they start repelling each other and move away from each other. This movement of these charges away from each other causes the stretching of the surface of the bubble and increase in the size of the soap bubble.
There is a force of tension in the bubble to oppose the force of repulsion between the charges.
When the force of repulsion between the charges and the tension force gets balanced, the stretching of the bubble stops due to the equilibrium attained between the forces.

Therefore, the size of the soap bubble increases when it is charged due to the repulsion between the charges on the surface of the soap bubble.

Hence, the correct option is C.

Note:
The students may think that due to the charges present on the surface of the soap bubble, there should be the electrostatic force of attraction between the charges and the size of the soap bubble should decrease. But the repulsion between the like charges on the bubble surface are more strong than the electrostatic force of attraction between the charges. Hence, the soap bubble size increases.