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Homework Help: Electromagnetic emission lines for a hydrogen atom

  1. Jan 2, 2015 #1
    1. The problem statement, all variables and given/known data
    Hi, I've been unable to find a relevant thread for a question that I've been stuck on for a couple of days now.

    Here it is;

    One of the electromagnetic emission lines for a hydrogen atom has wavelength 389nm. Assiming that this is a line from one of the Lyman (nf =1 ), Balmer (nf = 2) or Paschen (nf =3) series, what is the initial principle quantum number associated with the transitions? The Rydberg energy can be assumed to be 13.6eV

    2. Relevant equations
    ΔE=Ry(1/(ni)2 - 1/(nf)2))

    This is the formula used to attempt a solution

    There is another formula in my notes that may be helpful but i do not understand the symbols within it, it is;
    En,l = -Ry/(n-δl)2
    3. The attempt at a solution

    Using the equation ΔE=Ry(1/(ni)2 - 1/(nf)2)) and then equating this change in energy to the energy of light E=hc/λ.
    Then I insert various nf 's e.g. nf =1 for Lyman, then i would solve this for ni to see if i get an integer number, indicating that this is correct. I do this for nf =1,2 and 3 and I have never got an integer number leading me to believe my method is incorrect.

    Any help or insight would be appreciated,

    Thanks in advance, John.
  2. jcsd
  3. Jan 2, 2015 #2
  4. Jan 2, 2015 #3
    I forgot to mention doing these questions are purely for exam practice. So having the tables will no be an option.

    How would i do this in an exam? Simply put the numbers in as i have done and then chose the one which is closest to an integer value to be the correct one?

    Thank, John
  5. Jan 2, 2015 #4


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    Check your equation in regard to the placement of ni and nf.

    I think your approach to the problem is good.
  6. Jan 2, 2015 #5
    Ahh, yes, the ni and nf are the wrong way around. Thanks for your help :)
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