Consider an infinitely long hollow cylindrical wire, of inner radius R, and outer radius R2, and carrying a uniform current density amounting to a total current I. Use Ampère's law to determine the B-field in every point at a distance r from the wire's central axis, both within the wire as outside of it.

Consider an infinitely long hollow cylindrical wire, of inner radius R, and outer radius R2, and carrying a uniform current density amounting to a total current I. Use Ampère's law to determine the B-field in every point at a distance r from the wire's central axis, both within the wire as outside of it.