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Homework Help: How many traces observed in Stern-Gerlach?

  1. Apr 12, 2008 #1
    I am struggling with an Atoms and Nuclei past paper question, if someone can help please.

    In a Stern Gerlach experiment, how many traces on the plate would be observed if instead of hydrogen a)helium b)boron (atomic number 5), are used? [Hint: Boron will exist in 2L-S coupled states]

    I have no idea how to approach this problem. The previous part of the question asked to calculate the gap between the traces observed on the plate which is well known to be two traces, same for silver and other electrons with one electron in the outershell. The two traces problem I would do, but not the one I've mentioned above. Can someone help?
  2. jcsd
  3. Apr 12, 2008 #2


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    The number of traces is (2j+1), where j is the angular state of the atom.
  4. Apr 13, 2008 #3
    Hmmm as simple as that? It's just that its a whole 10 mark Question...
  5. Apr 13, 2008 #4
    Hi, Thanks Pam for your reply, much appreciated.

    I've tried to do the question I mentioned in the 1st post and get 1 trace for helium (L=0 , S=0 , J=L+S=0). But for Boron , as it has 2 L-S coupled states I get J=1/2 (2 traces) or J=3/4 (4 traces).

    Which one or a combination of the number of traces will it be for Boron I'm wondering...
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