A hollow sphere `A` is taken with charge `Q` on it. Another conductor `B` with charge `q` is inserted into the cavity keeping `B` insulated from `A`. Show that the total charge on the outside the surface of A is `(Q + q).`

Explanation

Charge q inside the cavity would induce a charge -q on the inner side of cavity and a charge `+`q would appear on the outer surface making the total charge on this surface equal to `( Q + q ) `.