Question

A ray of light passes through an equilateral prism such that the angle of incidence is equal to the angle of emergence and the latter is equal to $\frac{3}{4}$ the angle of prism. The angle of deviation is

• A. $25^{\circ }$
• B. $30^{\circ }$
• C. $45^{\circ }$
• D. $35^{\circ }$

Answer 1

Answer: (B)

It is observed if $\angle i=\angle e$ deviation produced is minimum.
and $i=\frac{A+{\delta }_m}{2}$
Here $A=60^{\circ }$
and $\angle i=\angle e=\frac{3}{4}\angle A$
$\therefore {\delta }_m=2\times \frac{3}{4}\times 60^{\circ }-60^{\circ }=30^{\circ }$