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Urgent Modern Physics question

  1. Apr 9, 2003 #1
    Here is a question that is giving me fits.

    An electron is trapped in an infinite quantum well. If the lowest energy transition is to produce a photon of 450nm-wavelength, what should be the well's width?

    Any help is appreciated. :)
  2. jcsd
  3. Apr 9, 2003 #2
    The energy eigenvalue equation for an electron in a 1-D infinite square well is:

    E(n) = (h^2 * n^2) / (8 * m * L^2),

    where L is the width of the well.

    A transition of energy states requires an emission or an absorption of a photon. The energy of a photon is:

    E = h * f,

    where f is the frequency of the photon.

    Now you've got the equations; all you have to do is plug and chug.

    Last edited by a moderator: Apr 9, 2003
  4. Apr 9, 2003 #3
    Nevermind got the frequency, my books equation says that there is a 2 on the bottom instead of an 8?
    Last edited by a moderator: Apr 9, 2003
  5. Apr 9, 2003 #4
    Call me an idiot but I'm still not getting the correct result. The answer is 0.064nm in width, but I keep getting extremely small numbers. Is there any additional help anyone might can give without totally giving away the problem? Thanks again!
  6. Apr 10, 2003 #5
    look closer at the 2 and 8 term, you will find that the difference is due to that h(bar)=h/(2*pi)

    I´m not sure what you are doing with the equation, but you are looking for a difference, a delta E, dose that help?

    Could you check you answer again, I´m getting an answer of ~ 6.4*10^(-10)???
  7. Apr 10, 2003 #6
    That is the correct answer you got, although I still wasn't able to get it before it was due. I can't figure out what I'm doing wrong. I'll try again later I guess. Thanks for the help. I think my problem lies in the frequency.
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