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Homework Help: Why a two-slit experiment with electrons is evidence electrons are waves?

  1. Apr 15, 2012 #1
    1. The problem statement, all variables and given/known data

    I'm just trying to prepare a study pack for my final. I am curious about something I have been reading over in my text book. Can someone please explain this for me?

    "Be able to explain why a two-slit experiment with electrons is evidence that electrons are waves"


    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Apr 15, 2012 #2
    Because an interference pattern (like the one you get in the two-slit experiment) only occurs when the objects interfering are waves, not particles.
  4. Apr 15, 2012 #3
    Hi nukeman,

    One of the key points of a two-slit experiment is that you can fire a single electron at a time at the slits, and if you don't detect which slit it goes through, you will still observe an interference pattern built up over time. This doesn't make sense if the electron is a classical particle going through one slit or the other; only by interpreting it as a wave could this be possible.

    In reality, the 'wavelike' behavior here is that of the electron's wavefunction, the probability distribution of where it could be. But a lot of the amazing / confusing results of early QM come from the conflation of what an object 'is' with its wavefunction. Anyway, this point is probably too subtle for your test, so don't worry about it; see the first paragraph about behavior observed when firing single electrons at a time :)

    Hope this helps,
    Bill Mills
    Last edited by a moderator: Apr 16, 2012
  5. Jun 10, 2012 #4

    Simon Bridge

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    For the sake of (being pedantic) completeness - the two slit experiment for electrons does not demonstrate that electrons are waves - exactly. It demonstrates wave-like behavior for electrons (which were not normally expected to display wave-like behavior) and so provides evidence for the general applicability of quantum wave mechanics... which predicts this behavior yea even for lumps of matter.

    The experiment does not tell us if the electron is a wave but that some of it's behavior is best modeled using the same math we normally use to describe waves. This is so close to he same thing, and so long-winded, that we don't normally bother with the distinction - but it's there, an important one, and creates a lot of confusion in students if they don't bear it in mind.

    @irfan104 - you are a tad off topic: how did you get on?
    If you are having this sort of trouble so close to an exam, then it is probably too late: you will find the method in your notes. You should already know it and have practiced it through the course.
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