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Wavelength forums

  1. May 1, 2005 #1
    I missed a day of class the other day so I dont have any notes on how to do this. If someone could please give me some tips or a site that helps explain how to do problems like these it would be greatly appriciated.

    Violet light falls on two slits separated by 1.92 10-5 m. A first-order line appears 13.1 mm from the central bright line on a screen 0.611 m from the slits. What is the wavelength of the violet light?

    I have about 10 problems do tomarrow very similar to this one and not a clue how to do them.
  2. jcsd
  3. May 1, 2005 #2


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  4. May 2, 2005 #3


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    The reference that Older Dan gave, is very useful.. You will find that you
    need to rewrite their equation to suit your data. Just be careful
    of units. To find the solution for lambda in nanometers, convert your data to the units they are using. (I have shown their units in parenthesis)

    e.g. lambda = [ymD]/d

    y - displacement from centerline (in cm)
    m - degree for order of line (1, 2, 3 etc..)
    D - screen distance (in cm)
    d - slit separation (in micrometers = 10^-6m)
    lambda - wavelength (nm)

    An http://eosweb.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html [Broken] (a double check for your calculated value) of wavelength for violet can be found by following the blue hyperlink.
    Last edited by a moderator: May 2, 2017
  5. May 4, 2005 #4


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    Reworking that equation again, I found the derived equation in my last post
    was incorrect! :blushing: (I'm surprised no one challenged me on that)

    correction: lambda = [dy]/[mD]

    y - displacement from centerline (m)
    m - degree for order of line (1, 2, 3 etc..)
    D - screen distance (m)
    d - slit separation (m)
    lambda - wavelength (m)

    Again be careful of units. Just convert to those in this equation. To express lambda in nanometers, multiply the resulting lambda by 10^9.
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