The Huygens principle proposes that every point on a wavefront can be considered a secondary source of spherical wavelets. The new wavefront is determined by the tangent lines to these secondary wavelets. Originally proposed by Christiaan Huygens in 1678, it provided a qualitative explanation for linear and spherical wave propagation, and the laws of reflection and refraction. However, it could not fully explain the phenomenon of diffraction. The principle can be applied to analyze the propagation of all wave types, including how light rays refract and reflect when changing mediums.

1. HUYGENS PRINCIPLE

2. WHAT IS IT?
Method of analysis applied to problems using wave propagation
Source: Wikipedia pictures

3. PROPOSAL
1678 from Christiaan Huygens
Every point on a wave-front may be considered a source of secondary spherical
wavelets which spread out in the forward direction at the speed of light. The new
wave-front is the tangential surface to all of these secondary wavelets.
(farside.ph.utexas.edu)
Assumed that secondary waves only travelled in “forward” direction
Provided a qualitative explanation of linear and spherical wave propagation
Derived the laws of reflection and refraction
Couldn’t explain the diffraction aspect

4. HYGUYENS PRINCIPLE
Steps in how to apply:
1. Start anywhere of the original wave-
front.
2. Draw a circle with any radius.
3. Repeat for the rest of the points you
choose with the same radius.
4. You now have your new wave-front

5. NOT ONLY LIGHT WAVES
Interference works for all different waves
Can show how a ray travels from one
medium to another
The figure shows how refractions works
Ray will refract since it’s a different
medium

6. REFLECTION
Can see how the rays would be reflected
Same pattern would happen
Rays are reflected downwards because the
angle of the mirror is pointed downwards
Originally moving from left to right

7. SOURCES
http://farside.ph.utexas.edu/teaching/302l/lectures/node150.html
http://physics.about.com/od/mathematicsofwaves/a/huygensprincip
l.htm
https://www.boundless.com/physics/textbooks/boundless-physics-
textbook/wave-optics-26/diffraction-175/huygens-principle-636-
5593/
http://www.mathpages.com/home/kmath242/kmath242.htm