Question

If a ray of light is incident on a plane mirror at an angle of incidence of 30${}^{\circ }$, then deviation produced by mirror is :

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

Answer 1

The correct option is D ${120}^{\circ }$

Deviation angle $=\pi -(i+r)$
$=\pi -({30}^{\circ }+{30}^{\circ })$ $(\because i=r)$
$=\pi -{60}^{\circ }$
$=\pi -\frac{\pi }{3}$
$=\frac{2\pi }{3}$
$={120}^{\circ }$