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Two small spheres each carrying a charge $q$ are placed $r$ metre apart. If one of the spheres is taken around the other in a circular path of radius $r$, the work done will be equal to:

1. Force between them × r
2. Force between them × 2\pi r
3. Force between them / 2\pi r
4. Zero

Correct answer: Zero

Solution

The electrostatic force between charges is conservative, so work done depends only on initial and final positions. Since the sphere is moved around a closed circular path and returns to the starting point, the net work done is zero.

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