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Homework Help: Bragg Diffraction Help

  1. Aug 21, 2007 #1
    Q: Electrons are incident on a crystal which can be thought of as a series of reflecting planes with spacing d=0.074nm. What Kinetic Energy should the electrons be given in order that at least four diffracton maxima are observable?

    The equations i think i have to use are nλ=2dsinθ, P=h/λ and then K=P^2/2m (m being mass of the electron) and form the question n=4.

    i'm supposed to get an answer of 1100.0eV.

    my problem is that i can't work out λ as i'm not given the angle θ, is there another set of equations i should be using? how do i get about this?

    thanks aidan.
  2. jcsd
  3. Aug 21, 2007 #2


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    Science Advisor
    Homework Helper

    The wavelength of the electron ( or anything else ) depends on it's momentum, wavelength = h/momentum.

    If you look at wikipedia for electron diffraction the equations are derived for momentum in terms of accelarating voltage.
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