Question

A ray of light is incident at ${60}^{\circ }$, on glass-air interface. Then the light ray will ___. (Given: Incident ray lies in glass).
Use : [${\mu }_g$ = $\sqrt{2}$ , ${\mu }_a$ = 1]

• A. pass undeviated
• B. reflect back into glass
• C. refract at ${90}^{\circ }$ to the normal
• D. refract at ${60}^{\circ }$ to the normal

Answer 1

The correct option is B

reflect back into glass

Given:
Angle of incidence, $i={60}^{\circ }$

Critical angle for the glass air interface is:
$C={\sin }^{-1}\frac{1}{{\mu }_w}$
$C={\sin }^{-1}\frac{1}{\sqrt{2}}$
$C={45}^{\circ }$
$⟹i>C$

As angle of incidence is greater than the critical angle, total internal reflection occurs. That is, light will reflect back into glass.