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Homework Help: Bragg condition

  1. Aug 21, 2009 #1
    1. The problem statement, all variables and given/known data

    The unit cell in a cubic crystal is 2.74Å. Determine the Bragg angle for reflections from the planes (200), (212) and (-112). [sorry i dunno how to put a bar on top of the numbers] if the x-ray wavelength used is 1.54Å

    2. Relevant equations
    Given Bragg's condition as 2d sinθ = nλ

    and d = 2π /|G|
    where G = ha* + kb* + lc* according to Laue condition.

    there's also d = a /√(h^2 + k^2 + l^2 )

    where a is the edge length.

    3. The attempt at a solution
    Since d is the distance between planes in atomic lattice, I guess it meant the distance of (200), (212) and (-112) to the origin. So I calculated is by finding the magnitude of G. Then i got confused by the two d equations. Should I use 2π or a to divide with |G| to find the Bragg angle? I thought a is more logical, but the 2π /|G|[/I] is making me confused. What are the difference between them?
    Last edited: Aug 21, 2009
  2. jcsd
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