The Young's double slit exp. and some general waves

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Discussion Overview

The discussion revolves around the Young's double slit experiment, focusing on the concept of secondary wavelets, also known as Huygen's wavelets. Participants explore theoretical implications and questions regarding the formation and behavior of these wavelets in relation to the experiment.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why secondary wavelets are considered to form only at the slits and not in front or behind them, suggesting a potential oversight in common explanations.
  • Another participant proposes that the "backlashes" of secondary wavelets interfere with each other and the original wavelet, leading to a single wave propagating outward, while noting that only wavelets centered in the slit can propagate through.
  • A participant expresses confusion about the lack of discussion regarding the potential 'backlash' effect of secondary wavelets affecting the source, indicating a gap in the literature they have encountered.

Areas of Agreement / Disagreement

Participants express differing views on the implications and interpretations of secondary wavelets, with no consensus reached on the questions posed regarding their behavior and effects.

Contextual Notes

Some assumptions about the behavior of wavelets and their interactions are not fully explored, and the discussion acknowledges the complexity of verifying the details of the Huygens wavelet interpretation.

WiFO215
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I was reading about the classic Young's double slit experiment and I had a few questions regarding secondary wavelets a.k.a Huygen's wavelets. I proceed with the following questions assuming you know the experiment.

The crucial point behind the explanation to the experiment is that light emerging from the original source, forms secondary wavelets at the 2 following slits. And from here on, books continue explaining things but I shall stop here for I have some questions.

Q1 - The secondary wavelets do not form only at the slit, but they form everywhere. Why do we consider the secondary wavelets only formed at the slit? Why not in front of it? Why not behind it?

Q2 - From the definition of secondary wavelets, I do not understand why nobody seems to discuss why they do produce a 'backlash' effect. Shouldn't the secondary wavelets travel backwards to affect the source itself and cause trouble?

The books I have come across seem to skip discussing these issues. Is there something I have not understood?
 
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My understanding is that the "backlashes" of the secondary wavelets interfere with each other and with the original wavelet, so that normally all you see is a single wave propagating outwards from the source. However, when the light passes through a slit, most of the wavelets generated before the slit get blocked by the wall; it's only those wavelets which are centered in the slit itself that can propagate through. And if the slit is thin enough, it looks like just a single wavelet at each slit.

I wouldn't take the Huygens wavelet interpretation too literally, though... it's a nice way to intuitively figure out what happens at something like a slit, but verifying the details gets extremely complicated.
 
anirudh215 said:
Q2 - From the definition of secondary wavelets, I do not understand why nobody seems to discuss why they do produce a 'backlash' effect. Shouldn't the secondary wavelets travel backwards to affect the source itself and cause trouble?
Read what I wrote about the obliquity factor in this thread: https://www.physicsforums.com/showthread.php?t=236864
 
Thanks Doc!
 

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