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Homework Help: QM solutions to the Schrodinger Equation

  1. Feb 10, 2014 #1
    1. The problem statement, all variables and given/known data

    Here's something that's confusing me. Say we have a potential

    V(x) = Vo if x < 0, x > a
    V(x) = 0 if 0 < x < a

    (yes I know the notation with greater than/equals etc isn't totally correct, but you know what I'm talking about.)

    In the middle section, ψ'' + k2ψ = 0

    Whenever I see the solutions it's always ψ = Asin(kx) + Bcos(kx) in the middle section where k2 = -2mE/h2

    In the right/left sections, ψ'' + f2ψ = 0, with f2 = -2m(E - V0)/h2

    The solutions here always seem to be complex exponentials.

    Can someone please explain the difference to me in the solutions?
  2. jcsd
  3. Feb 10, 2014 #2
    You must know the identities:
    exp(±iø) = cosø ± i*sinø
    So the two sets of solutions you're referring to are basically equivalent once you take the real part, only the exponential form turns out to be more practical in most cases because easier to manipulate.
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