A ray of light is incident on a plane mirror at an angle of $30^{\circ }$ with the surface of the mirror. What is the angle of reflection?

Solution

1. The angle of incidence $i$ is measured from the normal, so $$\begin{array}{rl}i& =90^{\circ }-30^{\circ }\\ & =60^{\circ }\end{array}$$.
2. According to the law of reflection, the angle of reflection $r$ is equal to the angle of incidence $i$.
3. Therefore, $r=60^{\circ }$.
4. Hence the answer is (B).