Question

A ray of light travelling from glass to air is incident at ${60}^{\circ }$ on the interface. The light ray will:

Use : [${\mu }_{glass}$ = $\sqrt{2}$, ${\mu }_{air}$ = 1]

• A. refract at ${30}^{\circ }$
• B. pass without any deviation
• C. refract at ${90}^{\circ }$
• D. reflect back into glass

Answer 1

The correct option is D

reflect back into glass

Rays of light is travelling from denser to rarer medium, so there is a chance of total internal reflection if angle of incidence is greater than the critical angle.
Let the critical angle be $i_c$
$i_c$ = ${\sin }^{-1}$ $\frac{1}{{\mu }_{glass}}$

$i_c$ = ${\sin }^{-1}$ $\frac{1}{\sqrt{2}}$ (${\because \mu }_g$ = $\sqrt{2}$)
We get $i_c={45}^{\circ }$

As, angle of incidence $>$ $i_c$

Hence, total internal reflection occurs.