A light ray is incident on a plane mirror at an angle of `30^(@)` with horizontal. At what angle with horizontal must a plane mirror be placed in its path so that it becomes vertically upwards after reflection?

Explanation

To make the reflected ray vertical, it should be rotated through and angle of `60^(@)`, So, the mirror should be tilted by `60^(@)//2=30^(@)` , as shown in Fig (b).