A point charge q is placed at the center of a hollow conducting sphere with inner radius a and outer radius b. What is the electric field at a point between the inner and outer surfaces (a < r < b)?

Core Concept

In electrostatic equilibrium, the electric field inside a conductor is zero. The region between the inner and outer surfaces (a < r < b) is within the conducting material of the sphere. Therefore, the electric field in this region is zero. The charge q at the center induces an equal and opposite charge on the inner surface of the conductor, but the field within the conductor itself must be zero.