Question

Two plane mirrors are inclined at an angle $\theta$ . It is found that a ray incident on one mirror at any angle is rendered parallel to itself after reflection from both the mirrors. The value of $\theta$ is

• A. $30^{\circ }$
• B. $60^{\circ }$
• C. $90^{\circ }$
• D. $120^{\circ }$

Answer 1

Answer: (C)

Incident ray and finally reflected ray are parallel to each other means $\delta =180^{\circ }$
From $\delta =360^{\circ }-2\theta$
$\Rightarrow 180^{\circ }=360^{\circ }-2\theta$
$\Rightarrow \theta =90^{\circ }$