A hollow metal sphere has inner radius a, outer radius b, and conductivity sigma. The current I is radially outward from the inner surface to the outer surface.
a) Find an expression for the electric field strength inside the metal as a function of the radius r from the center.
b) Evaluate the electric field strength at the inner surface of a copper sphere if 0.70cm and 28A.
c) Evaluate the electric field strength at the outer surface of a copper sphere if 2.9cm and 28A?