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Homework Help: Kinecti energy of the electron

  1. May 22, 2005 #1
    Hello, please help with the following question:

    the hydrogen atom is in ground state when a 15-eV photon interact with it and all the photon's energy is transferred to the electron,, freeing it from the atom.
    a) what is the energy of the ejected electron
    b) the de Brogle wavelength of the electron.

    I thought the energy is 15ev x 1.6 E-19 = 2.4 E-18 J, however, I am not sure the total energy is turned into kinetic energy

    I guess if the total energy is kinetic energy, then I can use 1/2 * mv^2 to get v, then
    wavelength = h/mv (where h is planck's constant)
    Am I right?

  2. jcsd
  3. May 22, 2005 #2
    Yep, sounds ok to me!
  4. May 22, 2005 #3


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    The total energy of the photon is not converted into kinetic energy. If the electron is in the ground state of hydrogen (something like -13.6 ev as I recall, but check on that) that much energy is needed to free it from the nucleus. Only the excess energy is going to result in kinetic energy.
  5. May 22, 2005 #4
    The amount of energy required to free electron is -13.6 ev, as you mentioned. This left 1.4 eV for kinetic energy. A total of 2.24 x E-19 J (1.4 x 1.6 E-19) is kinetic energy.

    v = 7.02 E5 m/v, That's what I got.
    Thanks alot
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