Question

A ray of light is incident on medium 1 with a refractive index of 1 from a medium 2 with a 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, we get:

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

r = ${45}^{\circ }$​​

As it is getting reflected by a plane mirror, light gets reflected at ${45}^{\circ }$​​​ by the plane mirror.

Again applying Snell's law, we get:

1 $\times$ $\frac{1}{\sqrt{2}}$ = $\sqrt{2}$ $\times$ $\sin$ r

r = ${30}^{\circ }$​​​

Hence, the deviation is given by:

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

= ${120}^{\circ }$​​​