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Homework Help: De Broglie Formula Application

  1. May 6, 2009 #1
    1. The problem statement, all variables and given/known data
    Estimate the wavelength of a 30 keV electron.

    2. Relevant equations
    p = h/λ
    E = hf

    3. The attempt at a solution
    The electron has 30 keV of mass-energy.
    As it is acting as a particle-wave, E = hf, so f = E/h = 30,000x1.6x10^-19/6.3X10^-34 = 7.619x10^18 Hz

    Now, v = fλ, so λ = v/f, but this is where I run into a problem, as I'm not told what speed the electron is travelling at - do I assume speed of light, or is there some other way?
  2. jcsd
  3. May 6, 2009 #2


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    Science Advisor
    Homework Helper

    Hi Pyroadept! :smile:

    If you can convert the eV into J, and if you know the mass of an electron, then you can calculate the speed from the energy. :wink:
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