Name: Brewster’s Law
Uploaded: 2019-07-19
Duration: 6 min 57 s
Description: Light is a transverse electromagnetic wave with electric field vectors vibrating in infinite directions perpendicular to the direction of propagation. Let's...

Question

What is polarisation by reflection. Deduce Brewster's law.

Accepted Answer

Polarisation By Reflection: If light incidents on a refractive surface so that the refracted light and the reflected light are at $90^{°}$ angle, then the reflected light will be linearly polarised, and the plane of polarisations will be parallel to the plane of the interface.

As per the Brewster’s Law, the maximum polarisation takes place when the angle is 90 degrees in between the reflected ray and refracted ray. The polarizations angle is called Brewster’s angle.

In this case $μ = \tan I_{p}$ where $I_{p}$ = Brewster 's angle

Refer to the figure , when light is incident at polarising angle $p$ on a refracting medium of refractive index $μ$ , Let $r$ be the angle of refraction, then according to the Snell's law.

$μ = \frac{\sin I_{p}}{\sin r}$ and from the brewster's Law $\frac{\sin I_{p}}{\sin r} = \tan p or \frac{\sin p}{\sin r} = \frac{\sin p}{\cos p} or \sin r = \cos p$

or $\sin r = \sin (90 - p) or r = 90 - p or r + p = 90$ .

Hence, when a ray of light incident at the polarising angle, the reflected ray is perpendicular to the refracted ray.

This is Brewster's law.

What is polarisation by reflection. Deduce Brewster's law.

Important Questions on Wave Optics

Learn and Prepare for any exam you want !