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Homework Help: Spectrum lines

  1. Nov 15, 2008 #1
    URGENT spectrum lines

    1. The problem statement, all variables and given/known data
    A diffraction grating (with 10,000 lines per cm) is held 2 meters from a Hydrogen lamp (lamp which emits
    Hydrogen’s spectrum). As you look through the diffraction grating a blue line is observed to lie 1.11 meters on either
    side of the lamp.
    1) What transition (from initial n to final n) does this blue line correspond to?
    2) What series does this line belong to?

    2. Relevant equations

    3. The attempt at a solution
    I've found these two relevant sites: http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html
    http://www.daviddarling.info/encyclopedia/H/hydrogen_spectrum.html But I'm still pretty confused with these two parts, I'm not sure where to start/what to do (I've already done all of the rest of the question)
  2. jcsd
  3. Nov 15, 2008 #2
    Re: URGENT spectrum lines

    What you can work out from those two parts ( The generalized Balmer formula ) is your observed wavelength.

    In which part of the electromagnetic spectrum is your observed colour? If I am now mistaken, once you know that, you'll be left with one uknown
  4. Nov 16, 2008 #3
    Re: URGENT spectrum lines

    I'm still confused, so I got theta = 0.51 rad and lambda (wavelength) = 485 nm, I know E = -13.6 eV/n^2

    How do I determine what transition it is? How do I get it? I know how to determine the series after I get this.
  5. Nov 16, 2008 #4
    Re: URGENT spectrum lines

    By now you should already know which series it is. In fact you didn't even have to solve anything to know which series it is as you were told the observed colour

    Look up the generalized Balmer formula again:

    [tex] \frac {1}{\lambda} = R ( \frac{1}{{n{_1}}^2}-\frac{1}{{n{_2}}^2}) [/tex]

    You already know the wavelength. And after you figure out which series it is ( look up the drawing in this link again http://www.daviddarling.info/encyclopedia/H/hydrogen_spectrum.html ) you'll be left with one unknow which you have to find.
  6. Nov 16, 2008 #5
    Re: URGENT spectrum lines

    Is it a 4-2 tansition?
  7. Nov 19, 2008 #6
    Re: URGENT spectrum lines

    :smile: Yep, if the wavelength is 485nm it should be 4-2
  8. Nov 19, 2008 #7
    Re: URGENT spectrum lines

    Perfect! Thanks!
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