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Homework Help: Diffraction Grating

  1. Nov 13, 2015 #1
    1. The problem statement, all variables and given/known data
    You shine a red (λ = 650 nm) laser beam and a green (λ = 532 nm) laser beam at a diffraction grating that has 400 slits/mm to create an interference pattern on a wall 2.30 m from the grating. If the two lasers are directly on top of each other, how far apart are the two m = 1 bright fringes from each other?

    2. Relevant equations

    3. The attempt at a solution

    (650*10^-9)(2.30) / (1/400)(.001) - (532*10^-9)(2.30) / (1/400)(.001) = 0.10856 m

    This is incorrect, however. What did I miss?
  2. jcsd
  3. Nov 13, 2015 #2


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    You calculation appears to assume a "small angle approximation". Check to see if the angles of diffraction for the two wavelengths are "small".
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