How does wavelength affect diffraction?

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Discussion Overview

The discussion centers around the relationship between wavelength and diffraction, exploring how different wavelengths of light, such as red and blue, affect the bending of light around objects. Participants examine the concepts of diffraction and interference, and how they interrelate, while also questioning the adequacy of analogies used to understand these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that longer wavelengths, like red light, can bend more easily around objects compared to shorter wavelengths, like blue light, using a string analogy to illustrate this idea.
  • Another participant challenges the string analogy, stating that light should not be imagined as a mechanical string that bends more easily with longer wavelengths.
  • A participant explains that diffraction is related to interference, specifically through the superposition of Huygens waves, and notes that the diffraction pattern depends on the wavelength.
  • There is a discussion about the relationship between diffraction and interference, with one participant expressing confusion about how they are connected.
  • One participant emphasizes that diffraction results from interference, particularly constructive interference, and mentions the appearance of maxima in the diffraction pattern.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the string analogy for understanding diffraction. There is also a lack of consensus on how to clearly relate diffraction and interference, with some participants asserting their connection while others seek clarification.

Contextual Notes

Some participants acknowledge the complexity of the concepts involved, noting that their understanding of diffraction and interference may be limited or incomplete. The discussion includes various interpretations and analogies that may not fully capture the underlying physics.

ranger
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Why does wavelength affect diffraction? For example, red light with a longer wavelength can easily bend around objects. I'm assuming that because of the characteristic longer wavelength, it can just easily bend (flex) as opposed to blue light with would have difficulty because of shorter wavelengths. I have this mental picture of red light like a piece of string, where the crests and troughs give the string an apparent wave appearance. Because the crests [and troughs] are further away from each other, the string can easily bend around objects. Is this the right view point?


--thanks.
 
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Hi,

have a look at this:
http://electron9.phys.utk.edu/phys136d/modules/m9/diff.htm

There you can see how the diffraction pattern depends on the wavelength
and why this is so.

I think you shouldn't imagine the light as a string that bends easier around objects if the wavelength is longer.
 
Last edited by a moderator:
Hi Edgardo,

Thanks for the link. But I fail gather any answer to my question. That article focuses, for the most part, on interference. Am I missing something?
 
Diffraction can be explained by interference, i.e. the superposition (summation) of the Huygens waves. If you calculate for example the diffraction pattern behind the slit you make use of that superposition.

The formula on the website (for the constructive interference) shows you where bright spots will appear behind the slit (maximum). The position of the spots depends on the wavelength.

The greater the wavelength, the greater the angle theta.

But you shouldn't imagine light being some sort of mechanical string that is bent around the opening. Maybe you could elaborate why you think that the "red light string" can bend around corner easier than a blue string.
 
I didnt know that diffraction and interference where related. I'm thinking that diffraction is the bending of light around an object and interference is where two or more interact, either constructively or destructively. How are these related?

I'm using the string analogy because I had no explanation as to how wavelength affects diffraction. If a piece of string [with crests and troughs] has longer wavelengths (red light), I picture it as being least distorted when compared to a straight piece of string. Then assuming that presence of crests and troughs adds stiffness, the red light string would bend easier that the blue light string [because less crests and troughs per unit time]. I know this is a weak analogy, but I really couldn't think of anything else.

The formula on the website (for the constructive interference) shows you where bright spots will appear behind the slit (maximum). The position of the spots depends on the wavelength.
Yea I know this. It depends on whether the waves are more or less in/out of phase [and wavelength affects this]. But this doesn't have anything to do with diffraction does it?

thanks again.
 
Last edited:
Diffraction is the bending of light into the geometrical shadow of an object as you stated correctly. But this is a result of interference.

Let's just concentrate on constructive interference. A maximum appears in the geometrical shadow (for example the first maximum). Thus, by the definition from above this is diffraction.

I recommend the book "Optics" by Eugene Hecht for further information on diffraction and interference.
 

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