Two plane mirrors are inclined to each other such that a ray of light incident on the first mirror $\left(M_1\right)$ and parallel to the second mirror $\left(M_2\right)$ is finally reflected from the second mirror $\left(M_2\right)$ and parallel to the first mirror $\left(M_1\right).$ The angle between the two mirrors will be:

• Correct answer
  A

  ${60}^o$
• B

  ${45}^o$
• C

  ${90}^o$
• D

  ${75}^o$

Solution

As given in question $AB\left|\right|CO$

$\therefore \angle ABF=\theta$

From laws of reflection

$\angle OBC=\theta$

Similarly $CD\Vert OB$

$\therefore \angle DCE=\theta$

Again from laws of reflection,

$\angle OCB=\theta$

$\therefore 3\theta ={180}^o$

$\Rightarrow \theta ={60}^o$

Hence, the correct answer is option: 'A'.