Question

A ray of light is incident on a ${60}^{\circ }$ prism at the minimum deviation position. The angle of refraction at the first face (i.e., incident face) of the prism is

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

Answer 1

The correct option is C ${30}^{\circ }$


Angle of prism, $A=r_1+r_2$ ​

For minimum deviation

$r_1=r_2=r$
$\therefore A=2r$
Given, $A={60}^{\circ }$

$\Rightarrow r=\frac{{60}^{\circ }}{2}={30}^{\circ }$

Hence, $\left(C\right)$ is the correct answer.