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Homework Help: Diffraction Grating and Maximums

  1. Apr 14, 2012 #1
    1. The problem statement, all variables and given/known data
    A grating has 728 lines per centimeter. Find the angles of the first three principal maxima above the central fringe when this grating is illuminated with 680 nm light.

    2. Relevant equations
    Our teacher briefly told us that N = # of slits / cm
    and that d sin θ = mλ, and that d = 1/N

    3. The attempt at a solution
    I substituted d=1/N into the d sin θ = mλ so it became sin θ / N = mλ.
    I then rearranged for θ to get arcsin(mNλ) = θ, and I plugged in values:
    first order --> arcsin(1 * 728 * 680e-9) and so on for m = 2, 3.
    However, I got it wrong.
    I tried converting N into lines / m instead of cm, but I still got it wrong.

    I know our teacher started to tell us this before class ended, but I feel that I am missing something
  2. jcsd
  3. Apr 14, 2012 #2
    never mind, I converted from cm into m in the opposite direction.
    my bad. don't answer this.
  4. Apr 15, 2012 #3
    In the equation d should be in metres
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