A Question about Diffraction....

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    Diffraction
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Discussion Overview

The discussion revolves around the concept of diffraction, particularly focusing on the conditions under which diffraction is considered "greater" or "maximum." Participants explore the relationship between the size of the slit and the wavelength of the wave, as well as the implications of Huygens' Principle in understanding diffraction patterns. The conversation includes both water waves and light waves, examining how these phenomena manifest visually and mathematically.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question the meaning of "greater diffraction," suggesting that if diffraction occurs when waves bend around obstacles, it seems to happen in all cases, not just when the slit is comparable to the wavelength.
  • One participant notes that the more light is diverted from the straight-through direction, the greater the diffraction, but this is challenged by observations of similar wave shapes in different scenarios.
  • Another participant describes greater diffraction as occurring when waves create a more perfect semi-circle around the barrier, particularly when the gap equals the wavelength.
  • It is mentioned that while the shape of the wave front may remain similar, the intensity and distribution of light change significantly with the width of the slit.
  • Participants discuss the mathematical relationship defining the angle of diffraction, indicating that as the slit width decreases, the angle increases, suggesting more diffraction.
  • There is a recognition that while less light may be present in wider angles, the intensity in off-axis areas can still be greater than expected, contributing to the discussion of "more bending of light."

Areas of Agreement / Disagreement

Participants express differing views on what constitutes "greater diffraction," with some emphasizing the visual and intensity aspects while others focus on the mathematical definitions. The discussion remains unresolved, with multiple competing interpretations of the concept.

Contextual Notes

Participants reference specific images to illustrate their points, but the discussion does not resolve the ambiguity surrounding the definitions and implications of diffraction in various contexts.

Kaneki123
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Okay...I have a question that, I have often read the statement in various topics on diffraction that "Diffraction is maximum when slit is comparable to wavelength of wave". Can someone point out what is exactly meant by ''greater or maximum diffraction'' here?...Like if we are going to talk about in the sense that "diffraction is greater when water waves, after passing through the slit, bend upto the "outer surface" of the slit", then is'nt that what happens in ''every'' diffraction, if we are to consider Hyugens Principle?...Any help is appreciated...
P.S: I know my question does not make much sense, so i will try my best to elaborate it in my replies...
 
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In the first image, the water waves after passing through the slit, form an almost semi-circular shape...However, in the second image, the water waves form the same almost semi-circular shape, even though gap between obstacles in the two images is not same...So what is this "greater diffraction"?...I hope my question makes some sense now...
 

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The more light is diverted from the straight-through horizontal direction, the greater is the diffraction.
 
pixel said:
The more light is diverted from the straight-through horizontal direction, the greater is the diffraction.
If you look very closely at the two images i posted, you can see that there is the same semi-circular shape of water waves in both images...So where is this "more bending of light in greater diffraction"?
 
Kaneki123 said:
If you look very closely at the two images i posted, you can see that there is the same semi-circular shape of water waves in both images...So where is this "more bending of light in greater diffraction"?
However, the intensity of the deflected light is much greater in one image than the other. If you were to place a screen behind the slit, in one case you'd see a small bright spot directly behind the slit and in the other you'd see a larger bright spot.
 
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I can only describe it simply as "When the waves create a more perfect semi-circle around the barrier, diffraction is considered greater (the gap being equal to the wavelength of the wave)".
 
Nugatory said:
However, the intensity of the deflected light is much greater in one image than the other. If you were to place a screen behind the slit, in one case you'd see a small bright spot directly behind the slit and in the other you'd see a larger bright spot.

But in the second case it would not be as bright as less light (due to smaller opening) is distributed over a wider range of angles.
 
Kaneki123 said:
If you look very closely at the two images i posted, you can see that there is the same semi-circular shape of water waves in both images...So where is this "more bending of light in greater diffraction"?

The equation for the angle, θ, of the first minimum with respect to the horizontal is sinθ = λ/w. This defines the extent of the main area of light on a screen. As you decrease w, the angle increases, i.e., more diffraction.
 
pixel said:
But in the second case it would not be as bright as less light (due to smaller opening) is distributed over a wider range of angles.
That is true. However, the off-axis areas are still brighter than they otherwise would be, a situation which is reasonably described by the informal "more bending of the light" that OP was asking about.
 
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InfiniteEntity said:
I can only describe it simply as "When the waves create a more perfect semi-circle around the barrier, diffraction is considered greater (the gap being equal to the wavelength of the wave)".
The shape of the wave front is basically to do with the overall (radial) path length and it looks pretty circular. That doesn't change much as the slot is widened - in fact. at infinity, the wave fronts are all circular. What does change A LOT is the width of the region of maximum wave power. The wider the slot, the narrow is the region. That is what Diffraction is all about.
 
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