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Homework Help: Inverse of the 1-D momentum operator

  1. May 8, 2012 #1
    1. The problem statement, all variables and given/known data

    I have to find the inverse of the 1-D momentum operator.

    2. Relevant equations

    3. The attempt at a solution

    Here's my solution:

    Pψ(x) = -iħ dψ/dx
    P-1[Pψ(x)] = P-1[-iħ dψ/dx]
    [P-1P]ψ(x) = -iħ [P-1 dψ/dx]
    Iψ(x) = -iħ [P-1 dψ/dx]
    ψ(x) = -iħ [P-1 dψ/dx]

    By induction, P-1f(x) = (i/ħ) ∫f(x)dx.

    Any mistakes?

    On a secondary note, I am not sure what property guarantees the validity of the second sentence: why should two equal expressions remain equal if they are being operated on by the same operator, that is, is an operator allowed to map an element from a vector space to only a single element (and not multiple elements) of the same vector space?

    Also, what property of an operator guarantees the validity of the third sentence: does the property of associaitivity hold for operators?

    Finally, I am wondering if I had started by calculating the expectation value of P-1 in momentum space and then use the Fourier transform of the wave functions, would I have got the right answer?
  2. jcsd
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