[College Physics] - Schrödinger's equation

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  • Artic_counter
    FFR Veteran
    • Jan 2007
    • 1002

    #1

    [College Physics] - Schrödinger's equation

    Hi guys, it's me again! Back with some questions! I'm at beginner level quantum theory btw!

    My first question (and the one I would like to be answered the most xD) is concerning The Particle in a Box. In this case it's a one dimensional box.

    With Schrödinger's equation, we can determine that the energy of a particle for a particular quantum number "n" is :

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

    Therefore

    En+1-En=(2n-1)*h^2/(8*m*L^2)

    Which means that the difference between two Energy levels will always be discrete. That's in contradiction with the correspondance principle.

    That fact is screwing with my head. Is there something I'm not understanding ?

    ----------------------------------------------------------------------------------------------------

    As for my second question, it's quite the challenge...

    Here's how it goes:

    In three dimensions, Schrödinger's equation for an electron is :

    1.PNG

    If the electrons are confined in a cube with borders equals to "L", the stationnary wave, solution of the equation is :

    2.PNG

    where nx, ny and nz are positive integers.

    If we impose the condition of periodicity in L so that :

    3.PNG

    Demonstrate that:

    4.PNG

    where

    5.PNG
    Last edited by Artic_counter; 02-16-2013, 11:25 PM.


  • Artic_counter
    FFR Veteran
    • Jan 2007
    • 1002

    #2
    Re: [College Physics] - Schrödinger's equation

    No one ?


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    • dag12
      FFR Simfile Author
      FFR Simfile Author
      • Dec 2004
      • 468

      #3
      Re: [College Physics] - Schrödinger's equation

      I can help. Give me a short while to respond.

      Comment

      • dag12
        FFR Simfile Author
        FFR Simfile Author
        • Dec 2004
        • 468

        #4
        Re: [College Physics] - Schrödinger's equation

        Regarding question 1, the problem is that you should be comparing it relative to the energy itself. That is, you should be calculating ΔE_n/E_n, which, as you will see, goes to zero as n→∞, in correspondence to the classical prediction.

        Regarding question 2, I was in the process of typing up a solution, but realized that it would be quicker to refer you to an external source. Reference this document:

        page 6.
        Note that the product of sines (as given by you) is only one such separable solution to the 3D particle in a box; a product of complex exponentials could also give you the correct answer.
        Last edited by dag12; 02-17-2013, 07:22 PM.

        Comment

        • Artic_counter
          FFR Veteran
          • Jan 2007
          • 1002

          #5
          Re: [College Physics] - Schrödinger's equation

          Thanks a lot! I've been spending a lot of time lately on those two thing!


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