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Below is the result of a single-slit experiment of light.

enter image description here

Alternate bright and dark fringes can be observed, where they represent the maxima and minima caused by constructive and destructive interferences respectively.

Below shows the diffraction of water waves.

enter image description here

The degree of diffraction increases as the gap size decreases.

My question: Why no alternate maxima and minima can be observed in the single-slit diffraction of water waves?

Is it because the amplitude of the 2nd-order maxima is too small so it is not that observable? Or it is due to other reasons?

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    $\begingroup$ Why do you say there are "no alternate maxima and minima" in the water patterns? I see them clearly. $\endgroup$
    – The Photon
    Commented May 26, 2020 at 15:03
  • $\begingroup$ @ThePhoton If that's the case, could we apply the formula asin(theta) = m(lambda) to the diffraction of water waves? $\endgroup$
    – mckong
    Commented May 26, 2020 at 15:09

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The link below shows water diffraction better than the images you found. https://www.quora.com/What-is-single-slit-interference

For water we have diffraction but there is no interference for the single slit, as you mentioned. In your images there is a slight pattern but that is likely due to the thickness causing extra reflections.

Water waves and light waves have many properties in common but are also fundamentally different. Light waves only travel from one atom/molecule to another and due to QM this path length is a multiple of the wavelength.

Water waves we travel in water molecules which we can touch and feel (have mass). Light waves travel in the vacuum and so we say they travel in the EM field.

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  • $\begingroup$ Could you kindly elaborate / explain why water waves couldn't show interference for single slit while light could? How does that related to the fundamental properties of water and light waves? $\endgroup$
    – mckong
    Commented May 28, 2020 at 16:29
  • $\begingroup$ If you have time to read my other answers here and those of other people you will learn the word "interference" is a historical, classical treatment of waves ... but photons do not truely cancel or interfere with each other in the EM field ..... so one can use Feynman theories to better explain single photon YDSE. Classical theories are good but do not explain all. $\endgroup$
    – PhysicsDave
    Commented May 31, 2020 at 1:35

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