Show that when light reflects from two mirrors that meet each other at a right angle, the outgoing ray is parallel to the incoming ray, as illustrated in the following figure.

Solution 2PE

Assume the incident ray reflects at an angle ∅ with the first mirror. Since both mirror meet each other at a right angle, so the first reflection ray forms a right triangle with the two mirrors as shown in below figure:

o - ∅

Now from the figure, the angle between the line parallel to the first mirror and outgoing ray is ∅2 and,

∅2 = 90o -

Substitute...