Question

A ray of light is incident at ${60}^{\circ }$, on the glass-air interface. Then the light ray will be ___.

Use : $[{\mu }_w=\sqrt{2}$ , ${\mu }_a=1]$

• A. refracts at 30°
• B. reflects back into glass
• C. refracts at 90°
• D. none of these

Answer 1

The correct option is B

reflects back into glass

$i_c$ = ${\sin }^{-1}$ $\frac{1}{{\mu }_w}$

$i_c$ = ${\sin }^{-1}$ $\frac{1}{\sqrt{2}}$ ${\mu }_w$ = $\sqrt{2}$
We get $i_c={45}^{\circ }$

As angle of incidence $>$ $i_c$

Hence Total Internal Reflection occurs.