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Diffraction in a single slit setting

  1. Oct 16, 2015 #1
    In a single slit diffraction setting, if the width of a slit is not much wider than the diameter of a particle such as a photon or an electron, would we still see diffraction bands? If so, is the number of bands / spots you see on the screen across is finite?

    I am a little confused by the mechanics and manifestation of the effects of diffraction.

    Is the appearance of bands of light (alternating light and dark bands) solely because of interference between the diffracted light at the top of the slit and the bottom of the slit, or is it also due to orders of diffraction?
  2. jcsd
  3. Oct 16, 2015 #2


    Staff: Mentor

    As far as we can tell today elementary particles such as a photon or electron do not have a diameter ie are point particles.

    For a correct quantum analysis, as well as the effect of width, see the following:

    Also note, despite what beginning texts will tell you, this has nothing to do with the so called wave particle duality which is basically a myth:

    In physics unfortunately sometimes what you learn starting out, or even at intermediate levels, has to be modified or even unlearned as you become more advanced. The wave-particle duality is one of those things. But don't get too worried about it, generally it doesn't cause too much trouble - its just when you want to be exact and examine issues of principle like you asked. Its one of those topics that far too much time can be spent discussing with quotes from this reference etc etc that leads to long threads that really don't accomplish much.

    Last edited: Oct 17, 2015
  4. Oct 16, 2015 #3

    Your comment was insightful as the links were useful to me, which is a lot. Appreciate it very much. Thanks for the tip of reading Ballentine as well. As you can tell, I am new to QM. Look forward to reading your threads.

  5. Oct 17, 2015 #4


    Staff: Mentor

    Hi Ramesh

    Thanks so much for your kind words.

    I think Ballentine will be a revelation especially chapter 3 where symmetry is seen as the real basis for things like Schodinder's equation.

    The following will likely interest you as it elucidates the essence of the formalism of QM:

    The essence is its the most reasonable generalised probability model that allows continuous transformation's between what's called pure states. You want continuous transformations because intuitively if a system goes through a state in one second it went through another state in half a second.

    That's the formalism - what it means is another matter.

    Last edited: Oct 17, 2015
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