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Bragg Law and Effect of Doubling Wavelength

  1. Apr 9, 2013 #1
    My lecturer discussed bragg's law a few weeks ago and described how the angle theta changes as the wavelength is doubled.

    I cant seem to duplicate his result.

    I know that the bragg condition for a maxima would reduce to : dsinθ=mλ when the wavelength is doubled.

    In his example he knew that maxima were observed at 20.5 and 44.5 degrees but he gave no other values.

    How would I go about predicting the angles at which the maximas are now observed ?
     
  2. jcsd
  3. Apr 9, 2013 #2

    mfb

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    If you double λ and m and d stay constant, sinθ doubles as well. You can calculate sinθ in your example.
     
  4. Apr 9, 2013 #3
    True, so sin(20.5) = 0.3502... This multiplied by 2 gives : 0.700.... Sin inverse of this gives 44.5 degrees.

    But if I double sin(44.5) I get a value larger than 1. How is it possible to take the sine inverse of this ?

    EDIT : Does this imply there is only one maxima now at 44.5 degrees ?
     
  5. Apr 10, 2013 #4

    mfb

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    The 44.5-maximum has no equivalent for the doubled wavelength, right.
     
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