Why Does Diffraction Occur Even When Wavelength Exceeds Aperture Width?

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Discussion Overview

The discussion revolves around the phenomenon of diffraction, particularly in the context of single-slit diffraction, and addresses the conditions under which diffraction occurs relative to the wavelength of light and the width of the aperture. Participants explore the implications of the relationship between wavelength and aperture width, and how this affects the resulting diffraction pattern.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that diffraction occurs when the wavelength is larger than the aperture width, while others challenge this notion, suggesting that diffraction can still occur even when the wavelength is smaller.
  • One participant introduces an equation, sin(theta) = wavelength/width opening, and questions its applicability when the wavelength exceeds the width, noting that it leads to an error in calculations.
  • Another participant explains that the equation is used to find the angles of dark fringes in a diffraction pattern and clarifies that when the wavelength is comparable to or larger than the slit width, the diffraction pattern changes significantly.
  • There is a discussion about how decreasing the width of the opening can have effects similar to increasing the wavelength, leading to a broader central maximum in the diffraction pattern.
  • Participants discuss the concept of phase differences in light waves and how they relate to constructive and destructive interference in diffraction patterns.
  • One participant raises a question about the maximum phase difference and its relationship to the width of the slit, seeking clarification on how this is determined.
  • Another participant mentions the phenomenon of diffraction occurring even with a half-infinite aperture, using the example of light grazing the edge of a razor blade.

Areas of Agreement / Disagreement

Participants express differing views on the conditions for diffraction, with some asserting that diffraction is contingent on the wavelength being larger than the aperture width, while others argue that diffraction occurs under a broader range of conditions. The discussion remains unresolved regarding the implications of these differing perspectives.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the relationship between wavelength and aperture width, as well as the mathematical steps involved in deriving the conditions for diffraction. Participants express uncertainty about the application of certain equations in specific scenarios.

  • #61
Ok thanks for the link, but anyone have an answer(s) to my last questions(in the same post)?
 
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  • #62
Anyone? Please?
 
  • #63
Please? I think this is my last question.
 
  • #64
Byrgg said:
Wow! Seriously? Is that all really correct? You're not joking?
No, I'm not joking :biggrin:
Byrgg said:
One more question, in multiple-slit diffraction, do the waves from one slit ever diffract into another one of the other slits?
Byrgg said:
but anyone have an answer(s) to my last questions(in the same post)??
Byrgg said:
Anyone? Please?
Byrgg said:
Please? I think this is my last question.
Patients if a virtue my friend, remember some of us are on different time zones :-p. No, as said previously, with any appature (including double slit), the maximum angle of diffraction is 90o, so when the wavefront reaches the other slit it is traveling perpendicular to the slit, so no diffraction will occur at that point and the waves are not diffracted back into the slit. However, the waves do interfere in the area between the slits and between the slits and the screen.
 
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  • #65
Ok, sorry about that, wasn't thinking of time zones. Is there any reason why it doesn't diffract through the other holes? Or does this not occur because the waves destructively interfere between gaps(do they destructively interfere there?). Even if there were multiple gaps, and only one had waves coming from it, it still wouldn't go through the other holes?
 
  • #66
Byrgg said:
Ok, sorry about that, wasn't thinking of time zones. Is there any reason why it doesn't diffract through the other holes? Or does this not occur because the waves destructively interfere between gaps(do they destructively interfere there?). Even if there were multiple gaps, and only one had waves coming from it, it still wouldn't go through the other holes?
Take a look at http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/doubleslitjavafigure1.jpg" , now the diffracted waves will br traveling either parallel to the slits or away from them. The waves do not diffract into the slits simply because there is nothing to diffracted through or around. Does that make sense?
 
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  • #67
Yeah, I think I get it now. They only diffract if they're going towards the gap or perpendicular right? Parallel wouldn't really do it I don't think... but then how exactly does diffraction around a corner work then? Say the waves were traveling along a barrier and came to a corner, that could be seen as a gap sort of couldn't it?, and don't the waves bend around corners?

Say a wave is moving forward, if it comes to a corner, then it continues forward, while diffracting around the corner as well right? The forward gap is perpendicular to the wave's direction, while the right/left gap is parallel. Is this explanation ok or should I try to make a diagram?
 
  • #68
Byrgg said:
Yeah, I think I get it now. They only diffract if they're going towards the gap or perpendicular right? Parallel wouldn't really do it I don't think... but then how exactly does diffraction around a corner work then? Say the waves were traveling along a barrier and came to a corner, that could be seen as a gap sort of couldn't it?, and don't the waves bend around corners?

Say a wave is moving forward, if it comes to a corner, then it continues forward, while diffracting around the corner as well right? The forward gap is perpendicular to the wave's direction, while the right/left gap is parallel. Is this explanation ok or should I try to make a diagram?
When sound gets diffracted around a corner, a component of the wave will be traveling towards the slit, because the waves are radiating from a point source, they are not traveling completely perpendicular to the slit. http://hyperphysics.phy-astr.gsu.edu/hbase/sound/imgsou/difr2.gif" Whereas in the double slit case, the source is in line with the slit and so the waves are either traveling away from the slit or perpendicular to it. Does that make sense?
 
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  • #69
Oh I think I see now, you said at a corner it still goes because it's partially going towards the slit right? You also mentioned that it's from a point source, that basically means it's radiating out and this is why it's partially aimed towards the slit right? If the point source was right in the wall(in theory) then would the waves still go around the corner?
 
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  • #70
Byrgg said:
Oh I think I see now, you said at a corner it still goes because it's partially going towards the slit right? You also mentioned that it's from a point source, that basically means it's radiating out and this is why it's partially aimed towards the slit right? If the point source was right in the wall(in theory) then would the waves still go around the corner?
Yeah that's it.
 
  • #71
Actually what I meant is if the source is right in the wall then isn't it sort of like already being diffracted through a single slit? The waves would be parallel(wavelength perpendicular) to the left/right slit. In this case the waves shouldn't pass through should they?
 

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