Question

A ray incident from a material of refractive index, $n=\frac{4}{3}$ to that of $n=\frac{3}{2}$. Find $\theta$ so that reflected light is completely polarised.

• A. ${\tan }^{-1}\left(\frac{3}{2}\right)$
• B. ${\tan }^{-1}\left(\frac{9}{8}\right)$
• C. ${\tan }^{-1}\left(\frac{4}{3}\right)$
• D. ${\tan }^{-1}\left(\frac{8}{3}\right)$

Answer 1

The correct option is B ${\tan }^{-1}\left(\frac{9}{8}\right)$


Completely polarised light is possible when reflected light is $\perp$ to refracted light.
By Snell's law,
$\frac{4}{3}\sin \theta =\frac{3}{2}\sin (90-\theta )$
$\tan \theta =\frac{9}{8}$