Q. Two plane mirrors are inclined to each other at an angle $\theta$. A ray of light is reflected first at one mirror and then at the other. The total deviation of the ray is
A) 2$\theta$
B) $240{^\circ} - 2\theta\ \ $
C) $360{^\circ} - 2\theta$
D) $180{^\circ} - \ \theta$
Explanation
(c) Total deviation
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$= (180{^\circ} - 2\alpha) + (180{^\circ} - 2\beta)$
$= 360{^\circ} - 2(\alpha + \beta)$
But $90{^\circ} - \alpha + 90{^\circ} - \beta + \theta = 180{^\circ}$
Or $\theta = \alpha + \beta$
$\therefore\ $Total deviation $= 360{^\circ} - 2\theta$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.