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Homework Help: Emission & Energy levels of Hydrogen Problem

  1. Dec 29, 2006 #1
    1. The problem statement, all variables and given/known data

    What values of n are involved in the transition that gives the rise to the emission of a 388-nm photon from hydrogen gas?

    2. Relevant equations

    wavelength = 388nm=3.88x10^-7 m
    R=1.097x10^7 m^-1

    E= hc/ wavelength

    3. The attempt at a solution

    E= hc/ wavelength=(6.63x10^-34)(3.00x10^8)/ (3.88x10^-7) = 5.13x10^-19 J = 3.206 eV

    En = -13.6eV / n^2
    n = - square root of (13.6/En) = -square root of (13.6/3.206) = - square root of 4.24 = -2.06

    n = 2 <- 1st excited state

    the answer is n=8 to n= 2.

    How would I know that it began from n=8 ?? Maybe there's an equation that I missed..
  2. jcsd
  3. Dec 29, 2006 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    The formula you need to know for this is the rydberg formula.

    [tex]\frac{1}{\lambda}=R_H \left(\frac{1}{(n_1)^2}-\frac{1}{(n_2)^2}\right)[/tex] where, [tex]n_1<n_2[/tex]
    Last edited: Dec 29, 2006
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