S is the surface of a lump of magnetic material.

Options

A. Lines of `vec(B)` are necessarily continuous across `S`.
B. Some lines of `vec(B)` must be discontinuous across `S`.
C. Lines of `vec(H)` are necessarily continuous across `S`.
D. Lines of `vec(H)` cannot all be continuous across `S`.

Answer

A, D

Explanation

The lines of `vec(B)` do not have a discontinuity upon a transition through the interface while the `vec(H)` lines have a dinuity due to surface magnetisation currents.