Understanding Huygens principle

1. LO7: UNDERSTANDING
HUYGENS PRINCIPLE WITH
3D WAVES
B Y: D E V I N G A M B L E 5 2 3 0 5 1 3 3
S E C T I O N : L E 2

2. 3D WAVES
Let’s first consider a 3-dimensional sound wave, propagating from
a single point source with constant wave speed, wavelength
and frequency. Since it is 3D, the wave would depend on the
directions x, y and z, as well as time t.
A sound wave will propagate in all directions, forming a wave front
that would look like a sphere

3. 3D WAVES
Next, lets look inside the spherical wave front. Here’s a cross-
section of the sphere we’re observing:
We can demonstrate this by choosing a set of points(sources) on
the sphere-cross section.
Huygens Principle states that any point on a
wave front is a source of spherical waves.
The resulting wave is determined by adding
all the waves from the point sources.

4. 3D WAVES
Then drawing circles of the same radii around each point(source).
Note that these new waves from each new point source will be 3D
spheres,
We are merely looking at a cross-section.
To determine the resultant wave from the original one, we simply draw
a circle tangent to all of the new circle-points we have just made

5. 3D WAVES
The resultant wave of our original green sphere will appear look like
this (in cross-section) after a certain time t:
There are many much more complicated applications of this
principle.
The point-sources on the original wave front are
not shown for clarity‘s sake.
*The thing to remember is that Huygens
Principle describes how waves continue to
propagate over time, and is useful in
understanding geometric optics for waves
involving light rays