Question

a point charge q is kept at a small height above a large plane surface.find electric flux linked with the surface

Answer 1

A point charge Q is kept at a small height above a large plane surface. let's make a symmetrical shape by using this plane surface. we can use cubical shape to enclose charge because it is symmetrical and contains large plane surface too.

now we know, there are six faces in a cube. so, electric lines of force divided in six equal parts.

[ note : flux is independent of position of charge in gaussian surface, it just equally for all faces of gaussian surface.]

so, electric flux through each face of cube = (Q/6)/$\epsilon_0$ [ from Gauss theorem ]

= Q/6$\epsilon_0$

hence,electric flux linked with the plane surface = Q/6$\epsilon_0$