Question

A ray of light is incident on medium 1 with the refractive index of 1 from a medium 2 with the refractive index of $\sqrt{2}$. Find the deviation of the emergent ray in the given diagram (with respect to first incident ray).

• A. 90°
• B. 180°
• C. 60°
• D. 120°

Answer 1

The correct option is D

120°

Applying Snell's law at first interface

$\sqrt{2}$ $\sin {30}^0$ = 1 $\sin r$

r = ${45}^{\circ }$

As it is getting reflected by a plane mirror, light gets reflected at 45° by the plane mirror.

Now, again this light will get refracted at the first surface.

Again applying Snell's law

1 $\times$ $\frac{1}{\sqrt{2}}$ = $\sqrt{2}$ $\times$ $\sin r$, $r$ = ${30}^{\circ }$

Hence the deviation is give by

= ${180}^{\circ }$ - ( ${30}^{\circ }$+ ${30}^{\circ }$)

= ${120}^{\circ }$