Huygens Principle: Light & Diffraction Explained

  • Context: Undergrad 
  • Thread starter Thread starter dsanz
  • Start date Start date
  • Tags Tags
    Huygens Principle
Click For Summary

Discussion Overview

The discussion revolves around Huygens Principle and its application to light diffraction, particularly in relation to the size of apertures and their effects on wave behavior. Participants explore the conditions under which diffraction occurs and the implications of Huygens Principle in various scenarios.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the necessity of an aperture being comparable in size to the wavelength for diffraction to occur, suggesting that Huygens Principle implies light should spread out through any slit.
  • Another participant asserts that diffraction does occur with wide apertures, but effects are only significant near the edges, and mentions "knife edge diffraction" as an example.
  • A participant expresses confusion over why light does not diffract through a door opening, despite the assertion that diffraction occurs with any aperture.
  • One response suggests that the rule about aperture size is a guideline for when diffraction effects become noticeable.
  • Another participant explains that while each point of a wavefront can be considered a light source, the superposition of contributions from a large aperture leads to cancellation in directions other than forward, thus limiting observable diffraction.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for diffraction and the applicability of Huygens Principle, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

There are assumptions regarding the definitions of diffraction and the conditions under which it is observed, as well as the implications of wavefront superposition that are not fully explored.

dsanz
Messages
42
Reaction score
2
Hello, I have the following question:

Physics books say that in order to see diffraction you need a wave to encounter an object that is comparable in size to the wavelength. This is presumably the reason why light does not bend through an opened door but sound does. My question is, what happens to Huygens Principle in the light scenario? If we can always consider the wavefront as another light source, wouldn't this mean that when light encounters ANY slit, no matter its size, the light will spread out in all directions? Does Huygens Principle simply not apply in some cases??

Thank you.
 
Science news on Phys.org
You do get diffraction with a wide aperture. The effects are significant only near the edges. In fact, you also get diffraction with only a single edge, i.e. a semi-infinitely wide aperture. A Google search for "knife edge diffraction" might turn up some pictures.

The following page has a Java applet that simulates diffraction for slits, circular and rectangular apertures, and knife edges (semi-infinite planes). You can vary the width of the aperture and observe the results.

http://www.falstad.com/diffraction/
 
Thanks for your reply jtbell. I am still confused as to why then does the aperture have to be comparable in size to the wavelength of the wave. If diffraction always occurs anyway, then why is it that light is supposedly not diffracted through a door opening?
 
I think that is just a rule of thumb for when the effect becomes apparent.
 
dsanz said:
If we can always consider the wavefront as another light source, wouldn't this mean that when light encounters ANY slit, no matter its size, the light will spread out in all directions? Does Huygens Principle simply not apply in some cases??

You can consider EACH POINT of the wavefront as another light source. For a narrow slit, this leaves you with a point source. For a door, you get a huge number of point sources. The superposition of these will only give reasonable intensity in the forward direction. In the other directions the contributions of all the point sources will just cancel out when superposed as the relative phase is pretty random in these directions if the slit is larger than a wavelength.
 
Cthugha I love you.
 
Please do not tell my girlfriend.
 
I am a straight guy, but sure, no problem
 

Similar threads

High School Can We Measure Diffraction Intensity Using Huygens' Principle?
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Calculating Intensity in Single Slit Diffraction Experiments
  • · Replies 17 ·
Replies
17
Views
3K
High School How do you explain a plane wavefront based on huygens' principle?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Huygen’s Principle in 2 Dimensions
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Can light always be treated as a physical object?
  • · Replies 15 ·
Replies
15
Views
6K
Graduate Huygens-Fresnel principle of diffraction
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Optics: Huygens' principle and bending of light
  • · Replies 2 ·
Replies
2
Views
2K
Graduate Huygens Principle - how to explain this with classical language?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Why Don't Spherical Waves Interfere According to Huygens Principle?
  • · Replies 18 ·
Replies
18
Views
5K
Graduate Online lecture about treatise on light by Huygens
  • · Replies 9 ·
Replies
9
Views
3K