Question

Two mirrors A and B are placed at a right angle to each other. A light ray is incident at an angle of 30° on mirror A as shown below. Find the angle of reflection for the ray incident on mirror B.

• A. 90°
• B. 60°
• C. 30°
• D. 20°

Answer 1

The correct option is B 60°

Let the angle of incidence and the angle of reflection on mirror A be $i_1$ and $r_1$ respectively,
the angle of incidence and the angle of reflection on mirror B be $i_{2}and{r}_2$ respectively.
Given,
$i_1$ = 30°

We know that
According to the law of reflection,
The angle of incidence (i) = The angle of reflection (r)
On Mirror A
$i_1=r_1=30°$


Since the angle between the mirrors A and B is 90°, the angle between the normals of mirrors A and B is also 90°.
Also,
$Sumofanglesinatriangle=180°\Rightarrow r_1+i_2+90°=180°\Rightarrow 30°+i_2+90°=180°\Rightarrow i_2=180°-120°\Rightarrow i_2=60°$

According to the law of reflection on mirror B
$i_2=r_2=60°$
Thus, the angle of reflection($r_2$) for the reflected ray from mirror B is 60°.