Two flat rectangular mirrors are set edge to edge and placed perpendicular to a flat nonreflecting surface. A light ray that reflects from mirror 1 at angle θM 1 then strikes the second mirror and reflects at θM 2 such that the angle between the ray reaching mirror 1 and the ray leaving mirror 2 is 180°. The angle between the two mirrors is
A)0°.
B)45°.
C)90°.
D)150°.
E)235°.

Question

​Two flat rectangular mirrors are set edge to edge and placed perpendicular to a flat nonreflecting surface. A light ray that reflects from mirror 1 at angle θM 1 then strikes the second mirror and reflects at θM 2 such that the angle between the ray reaching mirror 1 and the ray leaving mirror 2 is 180°. The angle between the two mirrors is
A)​0°.
B)​45°.
C)​90°.
D)​150°.
E)​235°.

Quizplus · Accepted Answer

Since the angle between the incoming ray and the outgoing ray is 180°, it implies that the ray reflects back on itself. This happens only when the two mirrors are perpendicular to each other. Thus, the angle between the two mirrors is 90°.

​Two Flat Rectangular Mirrors Are Set Edge to Edge and Placed

Two Flat Rectangular Mirrors Are Set Edge to Edge and Placed