惠更斯原理

Introduction

Today we will discuss Huygen's Principle, a mind blowing theory (at the time) that helped us understand diffraction, the bending of a wave around the edges of an opening or an obstacle. This principle explained why you can hear someone talking when you're standing around a corner wall -- it's because the other person's voice literally bends around the corner!

Wavefronts

First, we need to learn the concept of a wavefront. The simple definition of a wavefront is: "an imaginary surface joining all points in space that are reached at the same instant by a wave propagating through a medium".

This might sound confusing so check out this video for a better explanation:

Wavelets

Next we need to understand the concept of a wavelet. This definition is a bit more simple: a wavelet is just a small wave!

Huygen's Principle

Now that we have those two definitions, what Huygen's Principle states is that "every point on a wavefront is a source of wavelets, which spread forward at the same speed".

The implications of this idea are fascinating, especially when waves hit barriers.

Watch this video to see exactly how sound bends around walls.