Question

Two charges of magnitudes $-2Q$ and $+Q$ are located at points $(a,0)$ and $(4a,0)$ respectively. What is the electric flux due to these charges through a sphere of radius ${}^{\prime }3a^{\prime }$ with its centre at the origin?

Answer 1

By Gauss's law, the flux $\varphi =\frac{Q_{en}}{{ϵ}_0}$

Here the charge enclosed by sphere of radius 3a is $Q_{en}=-2Q$

Thus, $\varphi =\frac{-2Q}{{ϵ}_0}$