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Homework Help: Wavelength, emission spectrum, electron transitions

  1. Sep 23, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine the wavelength (in nm, to one decimal place) of the line in the emission spectrum of the He+ ion produced by a transition from n = 3 to n = 1.

    2. Relevant equations
    I used the Rydberg equation for this, although I'm not sure it is the correct one to use.

    3. The attempt at a solution
    Plugging in n1=1 and n2=3, I get an answer of 102.6nm. A search on wikipedia for the Lyman series also shows that transition from n=3 to n=1 is 102.6nm.

    The solution given, however, is 25.6nm. Obviously I am not understanding the question. Help would be appreciated.
  2. jcsd
  3. Sep 23, 2010 #2


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    2017 Award

    The Rydberg constant will be different for He+ than for hydrogen because He+ has more protons in its nucleus.
  4. Sep 23, 2010 #3


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    Science Advisor

    The equation you used is for Hydrogen. The He ion has a charge of +2, so the Rydberg constant is modified. Go back and look up the equation for how this Rydberg constant is derived.
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