Question

Two plane mirrors are inclined to each other at an angle of ${60}^{\circ }$. If a ray of light incident on the first mirror is parallel to the second mirror, it is reflected from the second mirror

• A. Perpendicular to the first mirror
• B. Parallel to the first mirror
• C. parallel to the second mirror
• D. Perpendicular to the second mirror.

Answer 1

Answer: (B)

Let $\theta$ be the angle between the two mirrors $O{M}_1$ and $O{M}_2$

The incident ray is parallel to mirror $O{M}_2$ and strikes the mirror $O{M}_1$ at an equal incidence angle.

From the given figure above

$\angle M_{1}BA=\angle OBC=\angle M_{1}O{M}_2=\theta$

Similarly $\angle M_{2}CD=\angle BCO=\angle M_{1}O{M}_2=\theta$

From $△OBC$

$3\theta ={180}^{\circ }⟹\theta ={60}^{\circ }$

So, reflected ray is parallel to first mirror.