In basic electrostatics, what happens to the size of a thin soap bubble when electric charge is placed on it and the charges spread uniformly over its surface?

Introduction / Context:
This question links electrostatics with surface tension in liquids. Soap bubbles are familiar from daily life, and understanding how they behave when charged helps you visualise the balance between electrical forces and surface tension forces on a thin liquid film.

Given Data / Assumptions:
• We have a thin spherical soap bubble in air.
• Some electric charge is placed on the bubble and spreads uniformly over its surface because the film behaves like a conductor.
• Temperature, external pressure and the amount of liquid making the film are assumed to remain the same initially.

Concept / Approach:
Two main forces act on the soap film. Surface tension tends to minimise the surface area, pulling the film inward and trying to reduce the radius. When charge is added, the like charges on the surface repel one another, producing an outward electrical pressure. The soap bubble reaches a new equilibrium when inward force from surface tension balances the outward electrostatic pressure. When you add charge, the outward pressure increases, so the radius must increase slightly to restore balance.

Step-by-Step Solution:
Step 1: Think of the bubble as a thin spherical conducting shell carrying charge on its surface. Step 2: On a charged conductor, the electric charges repel each other and reside on the outer surface, producing an outward electrostatic pressure. Step 3: The soap film already has inward pressure due to surface tension, which tries to make the bubble smaller. Step 4: When charge is added, the outward pressure increases while surface tension remains the same, so the bubble expands until a new equilibrium radius is reached. Step 5: Therefore, the net effect of placing charge on the soap bubble is that its radius increases.

Verification / Alternative check:
You can confirm this reasoning by recalling that in some physics demonstrations, a soap bubble is connected to a high voltage source, and observers notice a slight increase in size before the bubble may eventually burst if overcharged. This supports the idea that electrostatic repulsion stretches the film outward rather than shrinking it.

Why Other Options Are Wrong:
Its radius decreases: This would require the inward surface tension to dominate more strongly, but adding charge increases outward pressure, so the radius does not decrease.
The bubble bursts immediately: The bubble may burst if the charge is extremely high, but the question asks the general effect, which is initial expansion of the bubble.
The surface tension becomes zero: Surface tension is a property of the liquid and temperature. Charge does not make it zero; it only adds another force.
There is no appreciable change in size: Physics predicts a change in equilibrium radius because a new balance of forces is reached, so some increase must occur.

Common Pitfalls:
Students sometimes assume that any extra effect on the bubble will simply cause it to burst, without considering intermediate equilibrium states. Another common error is to ignore electrostatic pressure and think only of charge as a scalar quantity with no mechanical effect on the film. Remember that charges produce forces, and in this situation those forces act outward on the bubble surface.

Final Answer:
When electric charge is placed on a soap bubble, its radius increases because electrostatic repulsion stretches the film outward.