Question

A ray of light is incident on a plane mirror at an angle of $30^{\circ }$ . At what angle with the horizontal must a plane mirror be placed so that the reflected ray becomes vertically upwards?

• A. $40^{\circ }$
• B. $20^{\circ }$
• C. $30^{\circ }$
• D. $60^{\circ }$

Answer 1

Answer: (C)

When a light ray falls on a mirror at an angle $30^{\circ }$ , then the reflected ray will make the same angle with the plans as shown in Figure $(i)$
In order to make the reflected ray vertical, the mirror should be rotated at an angle of $60^{\circ }$ ,
So, the mirror should be tilted by $\frac{60^{\circ }}{2}=30^{\circ }$ as shown in Figure $(ii)$ .