Q. A ray of light incident normally on an isosceles right angled prism travels as shown in the figure. The least value of the refractive index of the prism must be
A) $\sqrt{2}$
B) $\sqrt{3}$
C) 1.5
D) 2.0
Explanation
(a) From figure it is clear that TIR takes place at surface $AC$ and $BC$
$i.e.\ 45{^\circ} > C$
$\Rightarrow \sin 45 > \sin C$
$\Rightarrow \frac{1}{\sqrt{2}} > \frac{1}{\mu} \Rightarrow \mu > \sqrt{2}$
Hence $\mu_{least} = \sqrt{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.