Question

A light ray is incident perpendicular to one face of a $90^{\circ}$ prism and is totally internally reflected at the glass-air interface. If the angle of reflection is $45^{\circ}$, we conclude that the refractive index $n$

• A. $n < \frac{1}{2}$
• B. $n >\sqrt{2}$
• C. $n > \frac{1}{\sqrt{2}}$
• D. $n < \sqrt{2}$

Answer 1

Answer: (B)

$n >\sqrt{2}$

Answer 2

Angle of incidence $i > C$ for total internal reflection. Here $i = 45^{\circ}$ inside the medium. $\therefore\quad45^{\circ} > sin^{-1}\left(1/n\right)$ $\Rightarrow n > \sqrt{2}.$