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Homework Help: Zeeman effect and defining the g_F Factor

  1. May 25, 2009 #1


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    1. The problem statement, all variables and given/known data

    A hydrogen atom is interacting with an external magnetic field.
    1. Derive the equation for the [tex]g_F[/tex]-factor of the hyperfine states.

    2. Relevant equations

    3. The attempt at a solution

    Okay, so the question asks to define the gF factor, however, I am not quite sure where to start.

    I know firstly that it is based on the diagram of the vector arrows, as (crudely drawn) attached:

    I also know the answer I need to get (it is mentioned in the notes):

    [tex] g_F = g_J\frac{F(F + 1) + j(j + 1) - I(I +1)}{2F(F + 1)} + \frac{\mu_N}{\mu_B}g_I \frac{F(F + 1) + I(I + 1) - j(j +1)}{2F(F + 1)}[/tex]

    Also, for the gJ, it starts with:

    [tex] H_J = \frac{\mu_N}{\hbar}(\hat{L} + 2\vec{S})\cdot \vec{B} = \frac{\mu_N}{\hbar}(\hat{J} + \vec{S})\cdot \vec{B} [/tex]

    and I know for gF, we have:

    [tex] H_J = \frac{\mu_B}{\hbar}(\hat{L} + 2\vec{S})\cdot \vec{B} - g_I ({\frac{\mu_N}{\hbar} \vec{I}\cdot \vec{B})[/tex]

    Anyone got any suggestions about what I should do first?


    Attached Files:

  2. jcsd
  3. May 27, 2009 #2


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    I suspect the approach would be to treat the external magnetic field as a perturbation to the internal magnetic field of the Hydrogen atom.

    In other words, [tex]\vec{B} = \vec{B}_{Internal} + \vec{B}_{External}[/tex].

    Considering [tex]\vec{B}_{Internal}[/tex] first, we can find the orbital angular momentum (l), spin angular momentum (s),ml,ms (or J,m?) eigenstate of the Hamiltonian (possibly after some simplifying assumptions?).

    We then apply first order perturbation theory for [tex]\vec{B}_{External}[/tex].

    Since you know the energy, you should be able to get the g factor.

    Hopefully, this is the way to go.
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