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Homework Help: Relativistic Bohr Atom and MacLaurin Series

  1. May 6, 2012 #1
    1. The problem statement, all variables and given/known data

    By expanding a MacLaurin Series show that
    [tex]E_{n}=\epsilon_{n} - \mu c^{2} = - \frac{w_{0}Z^{2}}{n^{2}}[1+\frac{\alpha^{2} Z^{2}}{n}(\frac{1}{k}-\frac{3}{4n})][/tex]

    2. Relevant equations

    Through a lengthy derivation I arrived at
    [tex]\epsilon_{n}=\frac{\mu c^2}{\sqrt{1+\frac{Z^{2}\alpha^{2}}{n_{r}+\sqrt{l^{2}-Z^{2}\alpha^{2}}}}}[/tex]
    I should add that k is what the text is using for the azimuthal quantum number, I used l in my derivation out of habit.
    3. The attempt at a solution
    I've got no ideas where to go with this thing. I should take advantage of identites
    Do I need to make some aggressive substitutions?
    Last edited: May 6, 2012
  2. jcsd
  3. May 7, 2012 #2
    I think I can make the following justifiable substitution
    [tex]\epsilon_{n}=\frac{\mu c^2}{\sqrt{1+\frac{Z^{2}\alpha^{2}}{n'}}}[/tex]
    Where [itex]n' = n_{r} + \sqrt{l^{2}-Z^{2} \alpha^{2}}[/itex]. But this still doesn't get me any closer to arriving at [itex]E_{n}=\epsilon_{n} - \mu c^{2} = - \frac{w_{0}Z^{2}}{n^{2}}[1+\frac{\alpha^{2} Z^{2}}{n}(\frac{1}{k}-\frac{3}{4n})][/itex] through a Maclaurin series.
  4. May 7, 2012 #3
    Ok, I may be closer... using the substitution above to put [itex]E_{n} = \epsilon_{n} - \mu c^{2}[/itex] in terms of n' I can calculate a Maclaurin series as follows
    [tex]- \mu c^{2} + \frac{\mu c^{2} \sqrt{n'}}{\alpha Z} - \frac{n^{3/2} (\mu c^{2} \alpha Z)}{2(\alpha^{4} Z^{4})} + \frac{n^{5/2} (3 \mu c^{2} \alpha Z)}{8 \alpha^{6} Z^{6}} - ...[/tex]
    Am I on the right track to the final [itex]E_{n}[/itex]?
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