Diffraction work differently on water waves vs light waves?

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Discussion Overview

The discussion revolves around the differences in diffraction patterns observed in water waves compared to light waves when passing through a wide slit. Participants explore the theoretical and experimental aspects of wave behavior, including the presence or absence of fringes and the implications of wave properties.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that water waves spreading through a wide slit do not produce fringes, while light waves do, suggesting a difference in behavior.
  • Others argue that surface waves and light waves, despite superficial similarities, have different dispersion properties that may account for the observed differences.
  • A participant claims that the same mathematical principles apply to both water and light waves regarding diffraction, asserting that the patterns can be similar if analyzed correctly.
  • Some participants question the clarity and accuracy of the visual representations of water wave diffraction, suggesting that the quality of experimental setups can affect observations.
  • There is a suggestion that side lobes or fringes can appear in water wave diffraction, depending on the conditions and properties of the waves involved.
  • A later reply emphasizes the importance of understanding the properties of incident waves to grasp diffraction and interference phenomena fully.

Areas of Agreement / Disagreement

Participants express differing views on whether fringes can be observed in water waves and the implications of these observations. There is no consensus on the extent to which water waves and light waves can be considered equivalent in their diffraction behavior.

Contextual Notes

Participants highlight limitations in experimental setups, such as the need for stroboscopic techniques to capture wave patterns accurately. The discussion also reflects varying interpretations of visual data and the conditions under which diffraction patterns are observed.

Karagoz
When the water waves go through one wide slit (slit wider than wave length), there's no fringes, the water waves spread all over the sides, like in this pic:

http://electron6.phys.utk.edu/light/images1-3/misc3b.jpg

or in this pic: http://philschatz.com/physics-book/resources/Figure_28_02_06a.jpg

But when light waves goes through a wide slit, it's split into multiple sides, there are fringes between them, it's not spread equally all over the place, like in this simulation (if you take width of the slit to 3000-5000 nm):

http://www.walter-fendt.de/html5/phen/singleslit_en.htm

Why there are no gaps when water waves go through a wide slit, but there are gaps when light waves go through a wide slit?
 
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Karagoz said:
Why there are no gaps when water waves go through a wide slit, but there are gaps when light waves go through a wide slit?

Surface waves and light waves have many superficial similarities (and methods of analyses), but they are not equivalent and have important differences- different dispersion properties, for example. One particularly spectacular example of this equivalence is the focusing of water waves by a 'lens' in a large test basin:

https://www.cambridge.org/core/jour...d-experiment/0E9C470B0A35698C77975F06C225AC4E

Don't take the cartoon analogies too seriously.
 
Karagoz said:
When the water waves go through one wide slit (slit wider than wave length), there's no fringes, the water waves spread all over the sides, like in this pic:

http://electron6.phys.utk.edu/light/images1-3/misc3b.jpg

or in this pic: http://philschatz.com/physics-book/resources/Figure_28_02_06a.jpg

But when light waves goes through a wide slit, it's split into multiple sides, there are fringes between them, it's not spread equally all over the place, like in this simulation (if you take width of the slit to 3000-5000 nm):

http://www.walter-fendt.de/html5/phen/singleslit_en.htm

Why there are no gaps when water waves go through a wide slit, but there are gaps when light waves go through a wide slit?

Exactly the same Maths applies to water waves and light waves, with respect to simple diffraction. The elementary links you refer to are elementary and they don't commit to any 'structure' off axis. If you just look at the visible wavelets on the water surface, it is hard to distinguish anything apart from in the main direction.
The ripple tank demo is pretty much a waste of time for serious analysis. The range of amplitudes that you can actually distinguish is very small and you cannot (at least, I cannot, after a lot of playing around) swear that you are seeing anything but the main 'forward' pattern. Otoh, the side lobes (fringes) of a slit pattern with light is much easier to spot (our eyes are very good with light!)
If you put in the appropriate values into that calculator (strictly to scale) you will get the same answer for light or water (or sound with water or air, for that matter).
 
Karagoz said:
So you mean it looks like this (if I don't see wrong, I see some:
http://figures.boundless-cdn.com/16694/full/iffraction-4-20wavelengths.png

Or this (at the left side): http://electron6.phys.utk.edu/light/images1-3/single1.jpg

Or this: https://phys.libretexts.org/@api/de...?revision=1&size=bestfit&width=226&height=162

Some fringes appear when water waves pass through singe wide slit?
The first picture shows water waves going through a wide slit, where we see a main beam which starts off parallel and then diverges. There are also side lobes visible. This is correct and is the same as with light and radio waves.
 
Karagoz said:
Some fringes appear when water waves pass through singe wide slit?

Yes, and there's a simple reason why. That reason is common for all types of waves, and understanding that reason is essential to fully understand any diffraction and interference phenomena.

Here's a hint: describe some properties of the incident wave(s). How can you create waves that look similar?
 
Karagoz said:
So you mean it looks like this (if I don't see wrong, I see some:
http://figures.boundless-cdn.com/16694/full/iffraction-4-20wavelengths.png

Or this (at the left side): http://electron6.phys.utk.edu/light/images1-3/single1.jpg

Or this: https://phys.libretexts.org/@api/de...?revision=1&size=bestfit&width=226&height=162

Some fringes appear when water waves pass through singe wide slit?
I am not convinced that the top figure is not a simulation. (double negative but you know what I mean). The other figures are better and must have taken quite an effort. The sorts of ripple tank / oscillator/ projector that schools tend to have available do not often produce such good images. Also you really need to be able to strobe the image so that the waves are frozen in time for the viewer.
But the existence of the 'null' rays should help to prove that Diffraction Works the same Everywhere.
 

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