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Wavelength, period of vibration in seconds

  1. Feb 17, 2015 #1
    < Mentor Note -- thread moved to HH from the technical physics forums, so no HH Template is shown >

    Okay, I am having trouble with the units. I have the values for the wavenumber and I am trying to find the period.
    These are the formulas that I am trying.
    T = 1/f ; f = c/lambda

    example: lambda = 3657 cm^-1 ; c = 2.998 x 10^8 m/s
    I am doing 2.998 x 10^8 m/s / (3657 cm^1 x (1 cm/0.01m))
    however, the unit for frequency is Hz = 1/s
    I am getting m^2 on the denominator.
    Am I using the right formulas?
    thanks!
     
    Last edited by a moderator: Feb 17, 2015
  2. jcsd
  3. Feb 17, 2015 #2

    berkeman

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    Staff: Mentor

    By wavenumber, do you mean wavelength? If so, wavelength has units of meters, not 1/meters.
     
  4. Feb 17, 2015 #3
    yes. it is the wavelength. But I am getting m^2
     
  5. Feb 17, 2015 #4

    berkeman

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    Staff: Mentor

    So you are given the wavelength, and want to find the period? Start off with the conversion equation that makes sense in terms of units...

    [tex]Period = \frac{Wavelength [m]}{Velocity [\frac{m}{s}]}[/tex]
     
  6. Feb 17, 2015 #5

    mfb

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    2016 Award

    Staff: Mentor

    A wavelength has units of meters, not inverse meters.
    Inverse meters suggest it is a wavenumber (usually called "k"). You can convert it to a wavelength, or directly use formulas with the wavenumber.
     
  7. Feb 17, 2015 #6

    berkeman

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    Staff: Mentor

    Not sure why my Latex isn't rendering correctly. It previews fine. Oh well, the old fashioned way:

    Period [in seconds] = Wavelength [in meters] / Velocity [in meters/second]

    EDIT -- I see now that using [ s ] without the spaces caused a strikethrough... Duh.
     
  8. Feb 17, 2015 #7
    I got it! Thank you!
     
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