Question

A beam of light after reflection from a plane mirror falls
on a circular scale 1.5 m from the mirror. On slightly
rotating the mirror, the light spot on the scale moves
through 10 cm. What is the angle of rotation of the
mirror? Assume that the mirror is almost at the centre
of the circular scale.​

Answer 1

Answer:

Angle = arc /radius = 10 cm/150cm = 0.066 radian

This is the angle through which reflected ray rotated.

For a fixed incident ray, the angle of the reflection is twice the angle through which the mirror has rotated.

So angle through which plane mirror rotated = 0.066/2 = 0.033 radian