Question

A light ray is incident on a flat surface, making an angle of 20° with the surface. What is the angle of incidence and angle of reflection respectively?

• A. ${20}^{\circ },{20}^{\circ }$
• B. ${20}^{\circ },{70}^{\circ }$
• C. ${70}^{\circ },{70}^{\circ }$
• D. ${70}^{\circ },{20}^{\circ }$

Answer 1

The correct option is C ${70}^{\circ },{70}^{\circ }$

Let the angle of incidence and angle of reflection be $i$ and $r$ respectively.
Since the angle between the surface and normal is ${90}^{\circ }$
$\therefore \angle i+{20}^{\circ }={90}^{\circ }$
$\Rightarrow \angle i={90}^{\circ }-{20}^{\circ }={70}^{\circ }$
We know that the law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection.
$\Rightarrow \angle i=\angle r={70}^{\circ }$