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Heisenberg's Uncertainty Principle

  1. Jul 28, 2011 #1
    Here's how I understand it:
    The light of a shorter wavelength disturbs the momentum of the electron, but shows the electron's position.
    Why doesn't the light of a longer wavelength disturb the momentum of the electron?
  2. jcsd
  3. Jul 28, 2011 #2
    A very similar thread was posted a few days ago.
  4. Jul 28, 2011 #3
    It was, but no one answered it...
  5. Jul 28, 2011 #4


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    It also disturbs, but less. How much it disturbs (how much the electron momentum may change) is inversily proportional to the wavelength of the photon.
    So - as you determine the electron position (using shorter wavelengths) more precisely, you simultaneously more disturb its momentum.
  6. Jul 28, 2011 #5
    Did you posted that?
    Anyway I'll try to explain.

    Light of longer wavelength means it has lesser energy and lesser momentum than that of light with shorter wavelength.Consequently it'll not disturb electron's momentum to a greater extent.

    When we measure the position of an electron by a photon bouncing off it the best we can do is to estimate its position within one photon wavelength,thus employing a longer wavelength will result in a blurry in electron's position.
  7. Jul 28, 2011 #6
    No, I didn't post it and thank you both for answering. I got the answer I was looking for.
  8. Jul 28, 2011 #7


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    The Heisenberg Uncertainty Principle is not a consequence result of disturbance during observations. I hope you don't walk away with that impression.
  9. Jul 31, 2011 #8
    Could you elaborate on what it means then?
  10. Jul 31, 2011 #9


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    Let's take spin. Suppose you measure a particle's z-component spin and it is always found to be "up", then you can say you have determined its z-component spin precisely. Also, since the result is always the same, this shows that measurement does not necessarily perturb the system. If you now measure its x-component spin, then immediately measure its z-component spin, you will no longer find the same value for the z-component spin. So the measurement of x-component spin disturbs the z-component spin. That is the Heisenberg uncertainty principle for x-component and z-component spin. (It's essentially the same story if you talk about position and momentum.)

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    Last edited by a moderator: Sep 25, 2014
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