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` can not be continuous across S

Answer

A, D

Explanation

The lines of magnetic field induction `vecB` are necessarily continuous across the surfaces S of a lump of magnetic material. Outside the lump of magnetic material, `H=B//mu_0` and inside the lump of magnetic material, `H=B//mu_0mu_r` where `mu_r` is the relative permeability of material. Thus the lines of H cannot all be continuous across surface S.