Making use of the formulation and the soulution of the foregoing problem, find the magnitude fo the force exerted by the charges bound on the surface of the dielectric on the point charge `q`.

Explanation

The force on the point chagre `q` is due to the bound chagres. This can be calculated from the field at this charge after extracing out the self field. This image field is
`E_("image") = (epsilon -1)/(epsilon +1) (q)/(4pi epsilon_(0) (2l)^(2))`
Thus, `F = (epsilon - 1)/(epsilon +1) (q^(2))/(16pi epsilon_(0) l^(2))`