Question

Which of the following graphs correctly represents the variation of angle of deviation $\left(\delta \right)$ with the variation in angle of incidence $i$ for a plane mirror?

• A.
• B.
• C.
• D.

Answer 1

The correct option is C


From the above diagram, we can deduce that,
$\delta =(180-(\angle i+\angle r\left)\right)\text{degrees}=(\pi -(i+r\left)\right)\text{rad}$

From the law of reflection,

$\angle i=\angle r$

So, we can rewrite the above equation as, $\delta =\pi -2i$

Comparing this with $y=mx+c$ , we can clearly say that, the graph between angle of deviation and angle of incidence is a straight line having a negative slope. Also, its intercepts are at $(0,\pi )$ and $(\frac{\pi }{2},0)$


$\begin{array}{c}\text{Why this Question}?\\ \text{This question provides more understanding to a student about angle of deviation.}\\ \text{Note:- Go through the definition of angle of deviation and its formula.}\end{array}$