Educator

Electric Potential, Part 4

• For a conductor, any excess charge must reside on the surface. Second, the electric field inside the conductor is zero. Third, E on the surface is perpendicular to the surface, and is given by sigma/epsilon_0, where sigma is the surface charge density. Fourth, the whole conductor is an equipotential region; i.e., all points on or within the conductor are at the same potential.
• If a conducting sphere has a total charge Q distributed on its surface, the potential inside the sphere is given by kQ/R, where R is the radius of the sphere.
• In a cavity within a conductor, the electric field is zero; if it were not, the inner surface of the conductor would not be an equipotential surface. The vanishing of E in the cavity explains why conductors are used as electrical shields.