Question

If a positive charge is given to a soap bubble, then its radius gets
A. radius decreases
B. radius increases
C. radius remains the same
D. decreases if the charges are negative.

Answer 1

Hint: The charge will get distributed uniformly on the surface of a soap bubble. Since there will be an external repulsive force because of the extra charge, there will be variation in the radius of the bubble. This is to attain the equilibrium condition.

Complete step-by-step solution:

When we take a look at the symmetry of the soap bubble, the charge will get distributed uniformly all over the surface of the bubble. The reason for such a phenomenon is as the like charges repel, they will tend to move even further apart. This can occur only in a way which is outward. This will take the soap surface also with them. And hence the increase in the restoring force of the soap film. And this surface tension will be equal to and the opposite of the electric force acting. And as a result of this, the equilibrium radius will be a new increased radius. This can occur in both positive and negatively charged bubbles due to their ionic similarity. Therefore we can conclude that when the soap bubble is given a positive charge or negative charge, then the radius of the soap bubble will increase.
Hence the correct answer is option B.

Note: We can see that the soap bubble will have two surfaces, the inner and the outer surface. This is because the surface tension will balance the outward force due to the pressure difference between the inside and the outside air of a soap bubble. The soap bubble is expanding in order to minimize surface tension.