Question

. Two plane mirrors PQ and QR are kept
perpendicular (at 90°) to each other. The
incident beam AB falls on one mirror PQ
at an angle of 20° to the mirror. Complete
the diagram to show the path of the
reflected ray.​

Answer 1

Answer:

parallel to the original ray

Let ray strikes the vertical mirror by angle of incidence θ. Then by joining the perpendiculars of two mirrors it is clear from the diagram that angle of incidence at horizontal mirror is (90−θ).

∴ reflected ray from horizontal mirror makes angle θ with the horizontal mirror also incident ray at vertical mirror makes angle θ with horizontal axis.

∴ reflected ray is parallel to the original ray.

This is true for two perpendicular mirrors fixed at any positions.