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I Quantum numbers - Total Energy and Orbital Momentum

  1. Apr 23, 2016 #1
    With the quantum numbers l=1, n=2 and m=-1 how do I calculate the total energy E, L2 (the square of the orbital momentum) and Lz (the z-component of the orbital angular momentum.

    I've been trying for two hours and am getting no were. Please help
  2. jcsd
  3. Apr 23, 2016 #2


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    Is this a homework problem? If so, it should be moved to the homework section, and should be put in the proper homework problem format.
  4. Apr 23, 2016 #3
    This was not "homework" I am just reading a physics book for my own enjoyment and I was reading a section and I have no clue how to get started. I could post it in homework if its more suitable?
  5. Apr 23, 2016 #4


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    Well, the actual way that these things are figured out is to start with Schrodinger's equation. That's a pretty complicated undertaking, which can't really be described in a post. If you just want to skip to the answers: For a hydrogen atom,

    [itex]E = \frac{- m q^4}{\hbar^2 n^2}[/itex]

    where [itex]m[/itex] is the mass of an electron, [itex]q[/itex] is the charge of an electron (in CSU units), [itex]n[/itex] is the principal quantum number, and [itex]\hbar[/itex] is Planck's constant.

    [itex]L = \sqrt{l(l+1)} \hbar[/itex]
    [itex]L_z = m \hbar[/itex]

    For an atom other than a hydrogen atom, replace [itex]q^4[/itex] by [itex]N^2q^4[/itex], where [itex]N[/itex] is the number of protons in the atom.
  6. Apr 23, 2016 #5


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    We consider this to be a "homework-like" problem. If your trouble is that you can't find the appropriate formulas, try here:


    Follow the links for "Principal quantum number", etc.

    If you have the formulas but you can't get the numbers to come out right, go to the Introductory Physics Homework forum:


    Post what you've done (show your work), and someone can probably find your mistake.

    (stevendaryl slipped in ahead of me)
  7. Apr 23, 2016 #6
    Thank you, that can get me started. I'll also go back to schrodingers equation.
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