A metal sphere of radius R, carrying charge 9, is surrounded by a thick concentric metal shell (inner radius a, outer radius b). The shell carries no net charge. Find the surface charge density at R; at 4, and at b. b) Find the potential at the center using infinity as the zero potential reference. Now the outer surface is grounded, which lowers the potential on the outer surface to zero (same infinity). How do your answers to a) and b) change?