Question

A ray of light is incident on a plane mirror AB. The angle of incidence is ${60}^{\circ }$. The ray is reflected from AB and strikes another plane mirror BC placed at right angles to mirror AB. The angle of reflection at BC is:

• A. ${135}^{\circ }$
• B. ${45}^{\circ }$
• C. ${60}^{\circ }$
• D. ${30}^{\circ }$

Answer 1

The correct option is D ${30}^{\circ }$

The question is represented in the attached figure.

$\angle PDN={60}^o$

Using laws of reflection, $\angle NDE={60}^o$

Using geometry, it can be proved that $\angle MED={30}^o$

Again using laws of reflection, $\angle MEQ={30}^o$

Hence, angle of reflection at surface BC is equal to ${30}^o$