Question

Find the current density on the conductor surface when a magnetic field H = 3cos x i + zcos x j A/m, for z>0 and zero, otherwise is applied to a perfectly conducting surface in xy plane.

(a) cos x i

(b) –cos x i

(c) cos x j

(d) –cos x j

This question was posed to me in an internship interview.

This key question is from Ampere Law in section Magnetostics of Electromagnetic Theory

Answer 1

Right option is (b) –cos x i

The best explanation: By Ampere law, Curl (H) = J. The curl of H will be i(-cos x) – j(0) + k(-z sin x) = -cos x i – zsin x k. In the xy plane, z = 0. Thus Curl(H) = J = -cos x i.