A hollow spherical shell of radius r has a uniform charge density `sigma`. It is kept in a cube of edge 3r such that the centre of the cube coincides with the centre of the shell. Calculate the electric flux that comes out of a face of the cube.

Explanation

Charge on the hallow sphere, `q=sigmaxx4 pi r^(2)`.
The flux through a single face of the cube, `phi^(1)=f/b=1/6. Q/epsi_(0) =(sigma xx 4 pi r^(2))/(6 epsi_(0))=(2pi r^(2) sigma)/(3 epsi_(0))`