Q 12-01-151JEE MainJEE Main 2018 (15 Apr, Shift 1)Easy
A charge $Q$ is placed at a distance $\dfrac a2$ above the centre of a square surface of side length $a$. The electric flux through the square surface due to the charge would be?
Answer: (A) $\dfrac{Q}{6\varepsilon_0}$
Imagine a cube of side $a$ with the square as one face. A point $\dfrac a2$ above the centre of that face is the centre of the cube.
By Gauss's law, the total flux through the cube is $\dfrac{Q}{\varepsilon_0}$, and by symmetry it divides equally among the six faces:
$$\phi = \frac{Q}{6\varepsilon_0}$$
Solution by Sreeraj P, M.Sc Physics