Question

A light ray is incident at ${30}^{\circ }$ on one of the two mirrors that are placed at right angle to each other. Find the angle of reflection for the ray reflected from mirror B.

• A. ${20}^{\circ }$
• B. ${30}^{\circ }$
• C. ${90}^{\circ }$
• D. ${60}^{\circ }$

Answer 1

The correct option is D ${60}^{\circ }$

Let the angle of incidence and angle of reflection on mirror A be $i_1$ and $r_1$ and on mirror B be $i_2$ and $r_2$ respectively. We know that the law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
$\Rightarrow \angle i_1=\angle r_1={30}^{\circ }$

On Mirror B
Angle between surface B and the incident ray

$\therefore \angle x+{90}^{\circ }+{60}^{\circ }={180}^{\circ }$
$\Rightarrow \angle x={180}^{\circ }-{150}^{\circ }={30}^{\circ }$

Angle between normal of surface B and the incident ray is ${60}^{\circ }$.

From first law of reflection
$\Rightarrow \angle i_2=\angle r_2={60}^{\circ }$