Question

A charge q is placed at the center of the cube of side l. What is the electric flux passing through two opposite faces of the cube?

Ans. $\frac{1}{3}\frac{q}{{\epsilon }_0}$

Answer 1

We know that cube has six faces so,

Flux through each face = $\frac{q}{6{\epsilon }_0}$

In the question flux through the two opposite faces is asked so,

Flux through two opposite faces is

$\frac{q}{6{\epsilon }_0}+\frac{q}{6{\epsilon }_0}=\frac{q}{3{\epsilon }_0}$

Hence, answer is $\frac{1}{3}\frac{q}{{\epsilon }_0}$