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Homework Help: X-ray diffraction

  1. Apr 24, 2010 #1
    1. The problem statement, all variables and given/known data
    First-order Bragg diffraction is observed at 25.9degrees relative to the crystal surface, with spacing between atoms of 0.26 nm.
    a)What is the wavelength of the X-rays?
    b)At what angle will second order be observed?


    2. Relevant equations
    m[tex]\lambda[/tex]=2dsin[tex]\phi[/tex]


    3. The attempt at a solution
    I solved part b: [tex]\lambda[/tex]=(2dsin[tex]\phi[/tex])=(2(.26*10^-9 m)(sin25.9deg)=.23nm which is correct.
    For part a I tried: sin[tex]\phi[/tex]=(m[tex]\lambda[/tex])/(2d)=((2)(.23*10^-9 m))/((2)(.26*10^-9))=62.2 Which is apparently close because mastering physics says,"Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures." Please help! I am down to one attempt and need to get it right this time. Thx!
     
  2. jcsd
  3. Apr 24, 2010 #2

    ideasrule

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    Homework Helper

    The answer to a) isn't 0.23nm; it's 0.22713692995120516100900531927073 nm. If you want to get an answer for b) that's accurate to 3 significant digits, you should use at least 4, preferably 5, of those digits.
     
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