A ray of light suffers minimum deviation, while passing through a prism of refractive index 1.5 and refracting angle 60${}^o$. Calculate the angle of deviation and angle of incidence.

Minimum deviation $\delta =2i-A$

where A is prism angle $A={60}^o$

For minimum angle the angle of refraction should be half of prism angle.

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

now using the snell's law

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

$sini=1.5sin30$

$i={48.6}^o$ , incidence angle

Minimum deviation $\delta =2i-A$

$\delta =2\times 48.6-60={37.9}^o$