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Homework Help: QM step potential

  1. Feb 24, 2008 #1
    1. The problem statement, all variables and given/known data
    A step potential is defined by: V(x) = 0 ( for for x <0 ) and V(x) = V0 ( for x >0 ). Hence the step occurs at the origin.
    Suggest a real physical situation, that might correspond to this idealized problem

    2. Relevant equations
    None needed.
    3. The attempt at a solution
    Looks simple, but I can't think of anything that this might correspond to. I was thinking about an electron being bound to an atom, and the step potential is like the ionizing potential, but since V0 goes from x = 0 to x = infinity, there can't be such potential...

    Or maybe a highly negative charged plate, so an electron moving at the positive direction would not pass through, but it is free to move in a negative direction ( 1D situation ).

    Does anybody have any ideas?
  2. jcsd
  3. Feb 24, 2008 #2
    You might imagine a marble being thrown at a concrete wall. Classically, they don't interact. When was the last time you saw the marble get inside the wall? I don't yet have a QM example for you.
  4. Feb 24, 2008 #3
    Thanks, that indeed makes sense.
  5. Feb 27, 2008 #4
    Since I tried solving one of these step potential questions the other day, I've been wondering what physical situation it corresponds to. The marble against the wall is not the case in question because for the cases I was given, the energy of the electron is greater than the step voltage. So you get a reflection coefficient and a transmission coefficient, both real. I have the idea of the junction between two dissimilar metals with different work functions. But I haven't been able to give physical meaning to the reflection coefficient.
  6. Feb 27, 2008 #5
    In my case, the energy of the electron is less then the step potential, so the marble example would apply. I could think of more examples if the potential was not infinite, but this complicate things.
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