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.*
$\begin{figure}\begin{center}\mbox{ \epsfig{file=PS/refl.ps,height=1.3333in}}\end{center}\end{figure}$

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:

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

Footnotes

. . . particles.^14.17: He was actually correct, but it is equally true that light consists of waves. If you are hoping that these apparently contradictory statements will be reconciled with common sense by the Chapter on QUANTUM MECHANICS, you are in for a disappointment. Common sense will have to be beaten into submission by the utterly implausible facts.

Next: Refraction Up: WAVES Previous: The Electromagnetic Spectrum

Jess H. Brewer - Last modified: Sun Nov 15 21:31:49 PST 2015