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Homework Help: QM: Spin and Angular Momentum.

  1. Oct 26, 2011 #1
    Hello All,

    Right now, I am trying to complete my QM assignment, but I am getting confused about the notation.

    So, the generalized angular momentum operator is represented as [itex]\hat{J}[/itex] and -j is the quantum # associated with the magnitude and [itex]m_{j}[/itex] is the quantum # associated with the projection of the angular momentum projection.
    Then given j=2, [itex]m_{j}[/itex]=-2,-1,0,1,2
    So now onto spin. The spin operator is [itex]\hat{S}[/itex] and similar s is the magnitude of the spin and [itex]m_{s}[/itex] is the projections. Then given s=1/2, [itex]m_{s}[/itex]=1/2,-1/2
    So far so good right?
    Now what is confusing to me is this: the question is asking for the expectation of the three components of angular momentum of a spin 5 particle. Does it mean s=5 or j=5?

    Another question is what does it mean by "the quantum number associated with the magnitude of the spin for a particle"? Are they asking for s?

  2. jcsd
  3. Oct 27, 2011 #2


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    Science Advisor
    Homework Helper

    I think they discard the orbital angular momentum, so that j=s=5. The magnitude is usually seen as the eigenvalue of S2.
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