Question

Explain polarisation of light by reflection and arrive at Brewster's law from it.

Answer 1

When unpolarised light is incident on the boundary between two transparent media, the reflected light is polarised with its electric vector perpendicular to the plane of incidence when the refracted and reflected rays make a right angle with each other.

Thus we have seen that when reflected wave is perpendicular to the refracted wave, the reflected wave is a totally polarised wave. The angle of incidence in this case is called Brewster’s angle and is denoted by $i_p$. We can see that $i_B$ is related to the refractive index of the denser medium. Since we have $i_p+r=\pi /2$,

We get from Snell’s law,

$\mu =\frac{sin{i}_p}{sinr}=\frac{sin{i}_p}{sin(\pi /2-i_p)}$

$\mu =\frac{sin{i}_p}{cos{i}_p}=tan{i}_p$

This is known as Brewster's Law.