Huygens’ principle

Physics 101

1. Huygens’ Principle Physics 101 Learning Objects Stacey Young

2. Who is Christiaan Huygens? Christiaan Huygens’ was born in 1629 into a Dutch family. In 1645, he went to University of Leiden to study law and mathematics. During his studies, he corresponded with other geniuses, such as Mersenne , who compared Huygens’ intelligence to the one of Archimedes’. So why is he important? Huygens’ discoveries after his studies and throughout his lifetime has further developed what we learn in Physics today, including the formula for deriving the period of a pendulum and of course, Huygens’ Principle!

3. Huygens’ Principle This principle describes a wave’s propagation using this procedure. Make some points on a wave front. Each point should be equally spaced from each other and equal distance from the original wave front Draw a circle around one point. Now draw the same sized circle around each point you have marked previously. Draw tangent lines to the circle and there you have your new wave.

4. Wave Propagation Plane Waves vs. Spherical Waves

5. Plane Waves Each new wave front of a plane wave is parallel to the previous wave. Imagine you dropped a pen into water horizontally. To determine the resulting wave using Huygens’ Principle, the points we draw are all on that linear horizontal line. The resulting wave will be linear as well.

6. Spherical Waves Each new wave front of a spherical wave is going to be spherical, only with a bigger radius than the original wave front. Instead of dropping a pen into the water, we dropped a baseball. To determine the resulting wave the points drawn on the original wave makes a circle. The tangents created by those points will create our resulting circle.

7. Checking for Understanding Using Huygens’ Principle, find the resulting wave front.