Name: Polarisation of Lightwaves
Uploaded: 2019-07-19
Duration: 3 min 1 s
Description: We know that light has dual nature. This video explains one of the most common optical phenomena, the wave nature of light and not the particle nature of light.

Question

State Brewster&rsquo;s law and show that when light is incident at polarizing angle, the reflected and refracted rays are mutually perpendicular to each other.

Accepted Answer

Brewster's law states that the tangent of the polarising angle is numerically equal to the refractive index of the medium at which partial reflection takes place.

let $i_{p}$ be the polarising angle, $μ$ be the refractive index of the medium and $r_{p}$ be the angle of refraction.

According to snell's law,

$μ = \frac{\sin i_{p}}{\sin r_{p}}$ ....(1)

Using Brewster's law: $μ = \tan i_{p}$ ....(2)

Using equation (1) and (2)

$\frac{\sin i_{p}}{\sin r_{p}} = \tan i_{p} \Rightarrow \frac{\sin i_{p}}{\sin r_{p}} = \frac{\sin i_{p}}{\cos i_{p}} \Rightarrow \sin r_{p} = \cos i_{p}$

$\sin r_{p} = \sin (90 ° - i_{p}) \Rightarrow r_{p} = 90 ° - i_{p} \Rightarrow r_{p} + i_{p} = 90 °$

The angle between reflected and refractive ray is given by,

$180 ° - i_{p} - r_{p} = 180 ° - (i_{p} + r_{p}) = 180 ° - 90 ° = 90 °$

Thus, the rays are perpendicular to each other.

State Brewster’s law and show that when light is incident at polarizing angle, the reflected and refracted rays are mutually perpendicular to each other.

Important Questions on Wave Theory of Light

Learn and Prepare for any exam you want !