Question

Two plane mirrors are inclined to each other as shown. A ray of light is incident at an angle of ${30}^o$ on one of them. The ray after reflection falls on second mirror and finally retraces its path. Calculate the angle between the mirrors.

• A. ${30}^o$
• B. ${60}^o$
• C. ${22.5}^o$
• D. ${45}^o$

Answer 1

The correct option is A ${30}^o$

On second mirror ray of light retraces its path

$\Rightarrow$ ray of light falls normally on the second mirror

$i.e.,$ $b=90$

$a=90-r_1$ $=60$

$\theta =180-\left(b+a\right)$

$={30}^0$

Hence,

option $\left(A\right)$ is correct answer.