When a plain mirror is rotated 10° in clockwise direction and incident ray is rotated by 5° in the counterclockwise direction,by what angle will the reflected ray rotate ?

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Solution

A ray of light is reflected by an angle (angle of incidence or angle of reflection; since both are equal) about the normal after reflection. Now, when the mirror itself is rotated by theta, the normal also rotates by theta. So the ray of light is reflected at an angle theta about the Normal. Hence the total angle becomes:

theta(angle between the incident ray and normal) + theta ( angle between the normal and the reflected ray)=2*theta.

Therfore the reflected ray will roatte by 2 x15 = 30 degrees

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