A metal sphere of radius R, carrying charge +q = 3 nC, is surrounded by a thick concentric metal shell (inner radius a, outer radius b, as in Fig. 2.48). The shell carries no net charge. a) calculate the surface charge density at radius r =R b) calculate the surface charge density at radius r = a c) calculate the surface charge density at radius r = b d) calculate the electric field at each radius FIGURE 2.48