1. The problem statement, all variables and given/known data I have a coaxial cable with current density Jo in the center, with radius a, going in -z_hat direction. This generates a magnetic field. The outside of the cable, radius c, also carries a current density Jout going in the +z_hat direction. This generates its own magnetic field. Find the value of the outside current density to make the magnetic field 0 for r > c 2. Relevant equations I used Ampere's equation. 3. The attempt at a solution I do not use Ampere's equation explicitly (starting from dot product and such), but conclude that H = 0 if the net current = 0. and then find out Jout in terms of Jo. Is this correct thinking? I mean, if I drew a loop that was outside of the coaxial cable, the Inet would be 0, but there is still an H-field being contributed by both the current densities. How else would I go solving this problem then? Thanks!