PHYSICS · Multi-part · CBSE · Physics · Light — Reflection and Refraction · Light — Reflection and Refraction
Problem
Two plane mirrors, labeled M1 and M2, are fastened at right angles to each other along a vertical edge so that they form the interior corner of a box. A narrow beam of light lies in a horizontal plane and approaches Mirror M1. Just before reaching M1 the beam travels due east and makes an angle of 30° with the normal to M1.
The beam reflects from M1, then immediately strikes M2, and finally leaves the mirror system after this second reflection.
Assume ideal specular reflection and answer the following.
(a) Determine the angle that the exiting beam makes with the due-east direction (the original propagation direction). Show all reasoning leading to your answer.
(b) Calculate the angle that the exiting beam makes with the normal to M2 at the point of its reflection from that mirror.
(c) A student claims that the pair of perpendicular mirrors behaves, for any incident ray confined to their plane, as though a single plane mirror were placed along the line that bisects the right angle between M1 and M2. Evaluate this claim for the situation above and justify your conclusion with geometrical reasoning.