Question

A light ray is incident at an angle of 60° on the mirror A which is placed at a right angle to a mirror B as shown in figure. Find the angle of reflection for the ray reflected from mirror B.

• A. 90°
• B. 60°
• C. 30°
• D. 45°

Answer 1

The correct option is C 30°

Let the angle of incidence and the angle of reflection on the mirror A be $i_1$ and $r_1$, and on the 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.

Therefore, $i_1=r_1=60°$
On Mirror A,
Let the angle between mirror A and the reflected ray be x, then,
$x+r_1={90}^o$
$x+{60}^o={90}^o$
$x={30}^o$

Since $\angle x$ and $\angle i_2$ are alternate angles, $\angle x=\angle i_2={30}^o$

Therefore, from the first law of reflection,
$i_2=r_2=30°$

Hence, angle of reflection for the ray reflected from mirror B is $30°$.