The sine of an angle divided by its cosine equals the tangent of the angle. So \(\tan{\theta_{\mathrm{B}}} = n_2/n_1\), or
If the angle of incidence for unpolarized light is something other than \(\theta_{\mathrm{B}}\), the reflected ray is partly polarized. If unpolarized light strikes the boundary perpendicular to it, so \(\theta_1 = 0\), there is no change in polarization of the reflected light.