Question

Two plane mirror are arranged at right angles to each other as shown in figure .A ray of light is incident on the horizontal mirror at an angle of $\theta$.For what value of $\theta$ the ray emerges parallel to the incoming ray after reflection from the vertical mirror?

Answer 1

For ray A and B to be parallel
$2\theta +2\alpha ={180}^{\circ }$
$\theta +\alpha ={90}^{\circ }$
$and\theta =\alpha$
$so\theta ={45}^{\circ }$