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 $\left(\right.i\left.\right)$
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 $\left(\right.ii\left.\right)$ .