Question

A soap bubble is given negative charge. Then its radius:
(a) decreases
(b) increases
(c) remains unchanged
(d) None of the above

Answer 1

If a bubble is charged then the charge is said to distribute uniformly on the surface of the charge. The uniform distribution of the charge is responsible for the minimization of the potential energy and no other distribution without making the change in the size of the bubble has lower energy.

Complete step by step answer: When we try to provide some charge on a soap bubble, then the repelling force between the charges acts and the charges try to be as far as possible to minimize the overall potential energy. The charges are uniformly distributed on the surface of the bubble. The hydrophilic ends of the soap molecules are usually in contact with the air. The outside and inside surfaces of the soap bubble and the iconic nature of the soap bubble helps in the uniform distribution of the charge on the surface of the soap bubble. If the charge on the soap bubble is negative, then the charges repel each other due to the electrostatic force. The negative charge will cause it to expand until the tension brings it into the equilibrium condition. In this case, the balancing force is the electrostatic force and the tension force. If the charge on the soap bubble is positive, then it will also be the same, and the radius of the bubble will increase.
Therefore, the radius of the soap bubble is increased and the correct option is option (b).

Note: A soap bubble is a spherical layer of soap film containing air or gas inside it. The soap film consists of two layers of soap molecules. One end of each soap molecule is always attracted to water and the other end of the soap molecule avoids the water.