S is the surface of a lump of magnetic material.

Options

A. Lines of `vecB` are necessarily continuous across S.
B. Some lines of `vecB` must be discontinuous across S.
C. Lines of `vecH` are necessarily continuous across S.
D. Lines of `vecH` cannot all be continuous across S.

Answer

A, D

Explanation

Lines of B are necessarily continuous across S but inside the lump,
`H = B/mu = (B)/(mu_0 mu_r)`