Question

A prism of refractive index $\sqrt{2}$ has a reflecting angle of 60${}^o$. At what angle must a ray incident on it so that it suffers minimum deviation?

Answer 1

For minimum deviation reflection angle should be half of prism angle.

So $r=A/2=60/2={30}^o$

Now using the Snell's law

$n_{air}sini=n_{prism}sinr$

$1\times sini=\sqrt{2}\times 0.5$

$sini=0.707$

$i={45}^o$