Two plane mirrors and intersect along a vertical edge and make an angle of

PHYSICS · Multi-part · AP · Physics 2: Algebra-based · Geometric Optics · Geometric Optics

Problem

Two plane mirrors

M_{1}

and

M_{2}

intersect along a vertical edge and make an angle of

60^{\circ}

. A narrow light beam in the plane of the mirrors strikes

M_{1}

at point

A

with an angle of incidence

25^{\circ}

(measured from the normal). The beam reflects from

M_{1}

, then strikes

M_{2}

at point

B

, and finally emerges into the room after its second reflection. (i) Calculate the angle of reflection at point

A

and hence determine the direction of the ray after the first reflection relative to

M_{1}

. (ii) Using suitable geometrical reasoning, find the angle of incidence of the ray on

M_{2}

at point

B

. (iii) Determine the angle between the initial incident beam and the emergent beam after the second reflection.