Question

A light ray is incident perpendicularly 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. $n>\frac{1}{\sqrt{2}}$
• B. $n>\sqrt{2}$
• C. $n<\frac{1}{\sqrt{2}}$
• D. $n<\sqrt{2}$

Answer 1

Answer: (B)

We know
${\theta }_{cric}=si{n}^{-1}\left(\frac{1}{n}\right)$

${45}^o>\theta$

$sin\left({45}^o\right)>\frac{1}{n}$

$\Rightarrow n>\sqrt{2}$