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Diffraction grating and wavelength

  1. May 1, 2015 #1

    CAH

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    Hi I've attached the question and mark scheme,

    I don't understand part 6(d)... Why have they used sin90?

    nλ=dsinθ

    If there is another order beam how can it be known the angel at which it exists from the zero order?
    Thanks
     

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  2. jcsd
  3. May 1, 2015 #2

    mfb

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    2016 Award

    Staff: Mentor

    That is the largest angle where you can observe anything and it maximizes the sine. Either something is observable at this or a smaller angle, or it is not observable at all.
    The 0th order is always at 0 degrees.
     
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