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Huygens principle

Christiaan Huygens described how to determine the path of waves through a medium.

Definition 1: The Huygens Principle

Every point of a wave front serves as a point source of spherical, secondary waves. After a time t, the new position of the wave front will be that of a surface tangent to the secondary waves.

Huygens principle applies to any wavefront, even those that are curved as you would get from a single point source. A simple example of the Huygens Principle is to consider the single wavefront in Figure Figure 1.

Figure 1: A single wavefront at time t acts as a series of point sources of circular waves that interfere to give a new wavefront at a time \(t+\Delta t\). The process continues and applies to any shape of waveform.

Example 1: Application of the Huygens principle


Given the wavefront,


use the Huygens Principle to determine the wavefront at a later time.


Draw circles at various points along the given wavefront


Join the circle crests to get the wavefront at a later time