If a soap bubble, having radius r, is charged to a charge density `sigma` and its radius is increased to R, then R equal to___________[T is the surface tension].

Explanation

To solve the problem, we need to analyze the situation of a soap bubble that is charged and has its radius changed from \( r \) to \( R \). We will use the principles of electrostatics and the mechanics of fluids.

### Step-by-Step Solution:

1. **Understanding the Problem**:
- We have a soap bubble with an initial radius \( r \) and surface charge density \( \sigma \).
- The radius of the bubble is increased to \( R \).
- We need to find the relationship between \( R \), \( r \), \( \sigma \), and the surface tension \( T \).
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