Reflection

The simplest thing waves do is to REFLECT off flat surfaces. Since billiard balls do the same thing quite nicely, this is not a particularly distinctive behaviour of waves - which was probably one of the reasons why Newton was convinced that light consisted of particles.^14.17 The reflection of waves looks something like Fig. 14.9.

**Figure:** *Reflection of a wave from a flat surface.*
$\begin{figure} \begin{center}\mbox{ \epsfig{file=PS/reflect.ps,height=1.25in} }\end{center}\end{figure}$

The incoming wave vector $\Vec{k}$ makes the same angle with the surface (or, equivalently, with the direction normal to the surface) as the outgoing wavevector $\Vec{k}'$ :

$\begin{displaymath}\theta \; = \; \theta' \end{displaymath}$

(14.41)

This is the most important property of reflection, and it can be stated in words thus:

$\fbox{The {\sl incident\/} [incoming] angle is equal to the {\sl reflected\/} [outgoing] angle. }$

Jess H. Brewer
1998-11-06