# symmetry-schematic-screens-v3-concise.mp4

Chapter section: Wave Propagation and Interference

Caption (verbatim):

Huygens–Fresnel principle

Image description (verbatim):

Huygens wavelets and their coherent sum as slits and screens are added

## Before the animation

Chapter lines 1199–1199:

We can extend this procedure to its limit and include infinitely many screens with infinitely many slits, and recover unobstructed propagation. In the following animation, we start with a plane wave and recover that same wave. This construction, which provides a bridge to Feynman’s path integral formulation of quantum mechanics, has its roots in Huygens’ wavelets from the late 1600s, extended by Fresnel to include interference in the early 1800s.

## After the animation

Chapter lines 1207–1207:

Let us now ask one more question. What happens to our tip-to-tail diagram of the path contributions when we vary the wavelength relative to the slit? As the wavelength becomes small, even a slight change in path length can produce a large phase change:

Chapter lines 1209–1212:

```math
\phi=\frac{2\pi L}{\lambda}=2\pi n+\theta,
\qquad 0\leq\theta<2\pi
```