Question

For light incident from air onto a slab of refractive index $ 2 $ , maximum possible angle of refraction is

• A. $ 90^{\circ} $
• B. $ 60^{\circ} $
• C. $ 45^{\circ} $
• D. $ 30^{\circ} $

Answer 1

Answer: (D)

The situation is shown in figure

Applying the Snells law at air-glass interface, we get
$\mu_{1}sini=\mu_{2}sin r$
or $sinr =\frac{\mu_{1}}{\mu_{2}}sin\,i=\frac{1}{2}sin\,i$
For the maximum angle of refraction, $i=90^{\circ}$
$\therefore sin\,r=\frac{1}{2} sin 90^{\circ}=\frac{1}{2}$
or $r=sin^{-1}\left(\frac{1}{2}\right)=30^{\circ}$