[twinklestar1012]

An outer shell of charge +Q is insulated by a light thread. There is an inner sphere inside which is earthed. The radii of the outer shell and inner sphere are b and a respectively. What is the potential of the inner sphere?

Initially, I thought the potential must be 0 because it is earthed, but when I do the integration (V = dE/ dr), I couldn't get it as 0

and i find it difficult to calculate the amount of induced charge on the inner sphere...

can anyone help me?

thanks!