Question

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

• A. ${45}^{\circ }$
• B. ${39}^{\circ }$
• C. ${20}^{\circ }$
• D. ${30}^{\circ }$

Answer 1

The correct option is D

${30}^{\circ }$

As angle of incidence is equal to the angle of emergence; the prism is in the minimum deviation position. Given $A={60}^{\circ }$ $i=\frac{3}{4}\times 60={45}^{\circ }$
$45=\frac{60+{\delta }_m}{2}$ or ${\delta }_m={30}^{\circ }$