11.3 CHAPTER 11. 2D AND3D WAVEFRONTS
���Figure 11.1: Wavefronts are imaginary lines joining waves that are inphase. In the
example, the wavefronts(shown by the grey, vertical lines) join all wavesat the crest of
their cycle.Consider three point sources of waves. If each source emits waves isotropically (i.e. the
same in all directions) we will get the situation shown in as shown in Figure 11.1.
We define a wavefront as the imaginary line that joins waves that are in phase. These
are indicated by the grey, vertical lines in Figure11.1. The points that arein phase can
be peaks, troughs or anything in between, it doesn’t matter which pointsyou choose as
long as they are in phase.11.3 The Huygens Principle ESCFB
Christiaan Huygens described how to determinethe path of waves through a medium.DEFINITION: The Huygens Principle
Each point on a wavefront acts like a point source of circular waves.
The waves emitted fromthese point sources interfere to form another
wavefront.