When a plane mirror is rotated through a certain angle the reflected ray turns through twice or much and how big?

Rotation of reflected ray

If a fixed ray is incident on a plane mirror at an angle i the angle of reflection is also equal to i, and so the angle between the two rays will be 2i. Suppose now that the mirror is rotated though an angle 8. The angle of incidence will increase by 8, and so also will the angle of reflection. The total angle between the two rays is now 2i + 28. Consequently, the angle of reflection will rotate through an angle of 28. Thus, the reflected ray rotates through twice the angle through which the mirror rotates.