Question

17. In the adjoining figure, two plane mirrors I and II are
placed perpendicular to each other. PM and QN are
perpendiculars to the mirrors I and II respectively. If an
incident ray strikes the mirror I at P and the reflected ray
strikes the mirror II at Q, then the value of x is​

Answer 1

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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.

Answer 2

Step-by-step explanation:

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.