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Homework Help: Derivation of momentum expectancy

  1. Nov 10, 2011 #1

    A_B

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    Hi,

    I'm working through Griffiths' Introduction to QM, In the derivation for the expectation value of momentum, he uses that
    [tex]\left( x \left. \left( \Psi^* \frac{\partial\Psi}{\partial x} - \frac{\partial \Psi^*}{\partial x}\Psi \right) \right) \right|_{-\infty}^{+\infty} = 0[/tex]

    Why is this so? It's easy to see that this is zero if the x weren't there, but I can't figure out why the limits are zero with the x in.

    Thanks,
    A_B
     
    Last edited: Nov 10, 2011
  2. jcsd
  3. Nov 10, 2011 #2
    since you said that it's easy to see that this is zeero if the x weren't there, wouldn't that mean by your reasoning that everything inside the brackets would equal zero.
     
  4. Nov 10, 2011 #3

    A_B

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    I'm sorry, the x is included in the evaluation, I edited the first post to make that clear, thanks.
     
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