Question

A ray of light is incident on a plane mirror at an angle of ${30}^{\circ }$ with its normal. The deviation produced in the ray is

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

Answer 1

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

Deviation of a light ray incident on the plane mirror making an angle of $\theta$ with normal is
$\delta ={180}^{\circ }-2\theta ={180}^{\circ }-{60}^{\circ }={120}^{\circ }$

Why this question? Concept: Angle of deviation by reflection (δ) is the angle between extended incident ray & reflected ray. Angle of deviation varies between $0^{\circ }$ to ${180}^{\circ }$