Question

Two plane mirrors are placed perpendicular to each other. A ray strikes one mirror and, after reflection, falls on the second mirror. The ray, after reflection from the second mirror, will emerge:

• A. perpendicular to the original ray
• B. parallel to the original ray
• C. at ${45}^{\circ }$ to the original ray
• D. at any angle to the original ray

Answer 1

The correct option is B parallel to the original ray

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

$\therefore$ reflected ray from horizontal mirror makes angle $\theta$ with the horizontal mirror also incident ray at vertical mirror makes angle $\theta$ with horizontal axis.

$\therefore$ reflected ray is parallel to the original ray.

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