When an unpolarized light falls at a particular angle on a glass… — Solution | JEE Physics

MCQEasyJEE 2026Diffraction & Polarisation

When an unpolarized light falls at a particular angle on a glass plate (placed in air), it is observed that the reflected beam is linearly polarized. The angle of refracted beam with respect to the normal is _. ( $\tan^{-1}(1.52) = 57.7^\circ$ , refractive indices of air and glass are $1.00$ and $1.52$ , respectively.)

A
$39.6^\circ$
B
$32.3^\circ$
C
$42.6^\circ$
D
$36.3^\circ$

Answer

Correct answer:B

Step-by-step solution

Standard Method

Given: Unpolarized light is incident on a glass plate in air, and the reflected beam is linearly polarized.

Find: The angle of the refracted beam with respect to the normal.

This is the condition of polarization by reflection at Brewster's angle.

\tan i_p = \mu

Using $\mu = 1.52$ ,

i_p = \tan^{-1}(1.52) = 57.7^\circ

At Brewster's angle, the reflected and refracted rays are perpendicular.

i_p + r = 90^\circ

So,

r = 90^\circ - 57.7^\circ = 32.3^\circ

Therefore, the angle of refraction is $32.3^\circ$ , so the correct option is B.

Common mistakes

Using Snell's law directly without recognizing Brewster's angle. This misses the special polarization condition. First identify that complete polarization on reflection means incidence at Brewster's angle.
Taking $57.7^\circ$ as the refracted angle. This is incorrect because $57.7^\circ$ is the polarizing angle of incidence, not the angle of refraction. Use $i_p + r = 90^\circ$ instead.
Using $r = i_p$ . The reflected and refracted rays are perpendicular at Brewster's angle, not equal. Therefore the correct relation is $r = 90^\circ - i_p$ .

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Step-by-step solution

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