A plane mirror is mounted on a rotational stage so that its surface can be rotated…
PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
A plane mirror is mounted on a rotational stage so that its surface can be rotated through a small angle α about a vertical axis. A fixed laser beam strikes the mirror before and after the rotation, and in both cases the reflected beams are observed on a distant screen.
(a) Derive an expression for the angle through which the direction of the reflected beam is deflected on the screen in terms of the mirror’s rotation angle α.
(b) The mirror is rotated through α=4.0∘. Calculate the corresponding angular deflection of the reflected beam.
(c) Provide a qualitative explanation, using geometrical reasoning, for why the reflected beam’s direction changes by a factor of two compared with the mirror’s rotation.