A narrow monochromatic light beam strikes a plane mirror that can be rotated about an axis lying in its plane. While the incident beam is kept fixed, the mirror is slowly rotated through a small angle Δθ.
(i) State the two laws of reflection for light from a plane surface.
(ii) With the help of a neat, labelled ray diagram, explain qualitatively how the direction of the reflected beam changes when the mirror is rotated through the angle Δθ. Demonstrate that the angular turn of the reflected beam is twice the angle through which the mirror is rotated, without using any trigonometric calculation.