A solid conducting sphere having charge Q is surrounded by an uncharged concentric conducting hollow spherical shell. Let the p.d. between the surface of the solid sphere and that of the outer surface of hollow shell be V. If now shell is given a charge - 3 Q, the new p.d. between the same two surfaces is?

Let potential at infinity equals to 0.R-radius of shell, r-radius of sphere Now, in first case, sphere has potential kQ/r. Shell has potential 0. Therefore,pd is kQ/r. Now after giving -3Q to the shell, potential of sphere becomes( kQ/r )-(3kQ/R). Potential of shell is -3 kQ/R. Therefore pd is (kQ/r - 3kQ/r)-(-3kQ/r)=kQ/r. That is, it remains same