- 2018: A charge Q is placed at the centre of a cube of side a. The electric flux through each face of the cube is: (A) Q/6ε0 (B) Q/8ε0 (C) Q/4ε0 (D) Q/ε0
The answer is (C).
The electric flux through a closed surface is given by Gauss’ law:
Φ = Q/ε0
In this case, the closed surface is a cube. The charge Q is located at the center of the cube, so the electric field lines will be radially outward from the charge.
The electric field lines will pass through each face of the cube, but they will not pass through the edges or corners of the cube. So, the total electric flux through the cube will be equal to the electric flux through each face of the cube.
The electric flux through each face of the cube is:
Φ = Q/4ε0
So, the total electric flux through the cube is:
Φ = 6 * Q/4ε0 = Q/2ε0
