Chapter 17.1, Problem 6PP

To determine

To Find: The angle between two mirrors.

Explanation of Solution

Introduction:

A retroreflector is a device which returns the incident radiation to the source with minimalistic scattering.

The angle between the two mirrors should be $90°$ . The reason is explained below.

  

An incident light ray falling on first mirror at angle $i_1$ will reflect at angle $r_1=i_1$ . The reflected light would fall at an $i_2=90°-r_1$ . Because $r_1=i_1$ and $r_2=i_2$ , $r_2=90°-i_1$ .

The angle between incident ray and final reflected ray will be:

  $\begin{array}{c}{i}_1+r_1+i_2+r_2=i_1+r_1+90°-r_1+90°-i_1\\ =180°\end{array}$

Conclusion:

Thus, the angle between two mirrors should be $90°$ .