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Wavelengths and Balmer series

  1. Feb 11, 2009 #1
    1. The problem statement, all variables and given/known data

    In the Balmer series, how many spectral lines have the wavelength greater than 400 nm?

    2. Relevant equations

    1/lambda= R(1/2^2-1/n^2)
    r=rhydberg constant 1.097x10^7
    n= 3,4,5....
    balmer series is visible light
    3. The attempt at a solution

    ok so i know the balmer series starts with 400 nanometers because its visible light, but i dont understand how to see how many spectral lines have wavelength greater.
  2. jcsd
  3. Feb 11, 2009 #2


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    Homework Helper

    You could just look up the Balmer Series in a book or on the web and count them.
    Or use the formula to calculate the wavelengths - put in n=3, calculate. Put in n=4, calculate. Pretty soon you will have all the wavelengths you need!
  4. Feb 11, 2009 #3
    ok. but when i do the calculating up to what number do i go? because i thought it went from 2 on.
  5. Feb 11, 2009 #4


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    Homework Helper

    Yes, it does go on forever - 2 to infinity. But after calculating 2 or 3 wavelengths, you will see that you don't have to do very many of them the answer your question.
  6. Feb 12, 2009 #5
    o ok i got it. wavelength decreases when you increase n
    thanks appreciate your response
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