Question

State and prove Brewster's law.

Answer 1

Brewster found experimentally that the reflected and refracted rays are at right angles to each other, when light is incident at polarising angle.
$\therefore i_p+{90}^o+r={180}^o$
$r={90}^o-i_p$
From Snell's law, $\frac{\sin i}{\sin r}=\mu$
$\therefore \frac{\sin i_p}{\sin (90-i_p)}=\mu$
$\frac{\sin i_p}{\cos i_p}=\mu$
(or) $\mu =\tan i_p$
Tangent of the polarising angle is numerically equal to the refractive index of the medium.