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Homework Help: Diffraction gratings - calculating the highest order maximum

  1. Aug 14, 2012 #1
    1. The problem statement, all variables and given/known data
    Monochromatic light of wavelength 694. nm is incident on a diffraction grating with 2192 lines per centimetre. What is the highest order maximum that can be observed?

    2. Relevant equations

    dsinθ = mλ

    3. The attempt at a solution

    d = 2192/cm = 21.92/m
    λ = 694 x 10 -9m
    sinθ = ??????????????????

    m = dsinθ/λ
    = (2192 x sinθ)/(694 x 10-9

    I think that this is the equation to use, but I'm not sure what angle to use. I initially tried 90 for θ, but then logically thinking about it, that wouldn't work as light travels only in straight lines. Not sure how to carry on from here. Some insight would help!


    n.b. Given answer = 6
  2. jcsd
  3. Aug 14, 2012 #2

    Simon Bridge

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    Homework Helper

    What is the highest angle possible?

    But I don't believe that value for d ... it's 11 orders of magnitude bigger than the wavelength!
    You only get diffraction if d is comparable to the wavelength otherwise we'd see baseball diffraction around doorways.
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