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Homework Help: Maximum wavelength

  1. Mar 23, 2013 #1
    1. The problem statement, all variables and given/known data

    Atomic sodium is studied by photoelectron spectroscopy. What is the maximum wavelength of the incident radiation that will ionize the most weakly held electrons in sodium and scatter them so that their de Broglie wavelength measures 3.091e-10 m?

    2. Relevant equations

    Energy of photon = h.c/λ

    kinetic energy = (1/2)*me*v²

    Binding Energy


    3. The attempt at a solution

    I've tryed this way but without results


    h= 6.626068 × 10-34
    me = 9.11*10^(-31)
    c = 299792458




    The binding energy for the most weakly held electrons i found in this table:


    Eb=30.81 ev = 4,94×10-18 j




    Whats wrong?
  2. jcsd
  3. Mar 23, 2013 #2


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    2017 Award

    Staff: Mentor

    The value for the ionization energy is wrong. It should be about 5 eV, not 30 eV.
    The table you linked has values for some other electrons, I think.

    I did not check your calculations - without any explanation what you are doing, this is not fun.
  4. Mar 23, 2013 #3

    But the question is self explanatory. You have a incident photon that will ionize a sodium atom and scatter a electron with a wavelenght equals 3.091e-10. I've just done a energy balance. The energy of the photon must be equal to the kinetic energy of the electron plus binding energy.

    Binding energy = 5.1 ev accord with my periodic table from MIT.
  5. Mar 23, 2013 #4
    I solved. I made ​​a mistake in the calculations
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