Question

A prism has a refracting angle of $60^o.$ When placed in the position of minimum deviation, it produces a deviation of $30^o.$ The angle of incidence is

• A. $30^{\circ }$
• B. $45^{\circ }$
• C. $15^{\circ }$
• D. $60^{\circ }$

Answer 1

Answer: (B)

In minimum deviation of prism angle of incidence $i$ becomes equal to the angle of emergence $e$ and the refracted ray becomes parallel to the base of the prism.

For prism, $i+e={\delta }_m+A$ ; where $A$ is refracting angle of prism, since $i=e$ ,
So, $i=\frac{{\delta }_m+A}{2}=\frac{30^{\circ }+60^{\circ }}{2}=45^{\circ }$ .