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

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SUMMARY

The discussion centers on the Young's double slit experiment and the concept of secondary wavelets, also known as Huygens' wavelets. Participants explore why secondary wavelets are considered to form only at the slits and not in other areas, as well as the implications of a 'backlash' effect from these wavelets. It is established that while secondary wavelets theoretically form everywhere, only those at the slits propagate through due to obstruction by the slit walls. The conversation highlights the complexity of accurately interpreting Huygens' principle in practical scenarios.

PREREQUISITES
  • Understanding of Huygens' principle
  • Familiarity with wave propagation concepts
  • Basic knowledge of the Young's double slit experiment
  • Concept of interference patterns in physics
NEXT STEPS
  • Research the mathematical formulation of Huygens' principle
  • Explore the implications of wavelet theory in quantum mechanics
  • Study the effects of slit width on interference patterns
  • Investigate the concept of wave-particle duality in light
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Students of physics, educators explaining wave phenomena, and researchers interested in the foundational principles of optics and wave behavior.

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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