For a fixed incident light ray, if the mirror be rotated through and angle `theta` (about an axis which lies in the plane of mirror and perpendicular to the plane of incidence), show that the reflected ray turns through an angle 2`theta` in same sense.

Explanation

see figure `M_(1), N_(1)` and `R_(1)` indicate the initial positon of mirror, initial position of mirror, initial normal and initial direction of reflected light may respectively. `M_(2). N_(2)` and `R_(2)` indicate the final positon of mirror,final normal and final direction of reflected light ray respectively. From figure it is clear that `/_ABC = 2phi + delta = 2(phi + theta)` or `delta = 2theta`