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A point charge q is located exactly at the centre of a cube of edge a. What is the electric flux passing through any one face of the cube?

1. q/(6*epsilon0)
2. q/(epsilon0*a²)
3. q/(4*pi*epsilon0*a²)
4. q/epsilon0

Correct answer: q/(6*epsilon0)

Solution

By Gauss's law the total flux through the closed cube is q/epsilon0. Since the charge is at the centre, the six faces are equivalent by symmetry, so each face receives one-sixth of the total flux.

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