Magnetic field-line refraction at a permeability interface
= Magnetic field-line refraction at a permeability interface
For linear isotropic media with no free sheet current, continuity of normal $B$ and tangential $H$ gives $\tan\theta_2/\tan\theta_1=\mu_2/\mu_1$, where the angles are measured from the normal. It is a consequence of the two different magnetic <boundary conditions>, not continuity of every component of $B$.