Q 1.18: A point charge is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Fig. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)
Let us assume that the charge is at the centre of cube with edge 10 cm.
Using Gauss's law , we know that the flux of electric field through any closed surface S is times the total charge enclosed by S.
where, q = net charge enclosed and = permittivity of free space (constant)
Therefore, flux through the cube:
Due to symmetry, we can conclude that the flux through each side of the cube, , will be equal.