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Photoelectric Effect - Energy Level (hydrogen)

  1. Nov 21, 2011 #1
    1. The problem statement, all variables and given/known data
    Consider a photon that is barely capable of causing a photoelectric effect when it strikes a sodium plate having a work function of 2.55eV.

    2. Relevant equations
    Find the minimum energy level n for a hydrogen atom that can be ionized by such a photon, and the speed of the released electron far from the nucleus.

    Can someone explain to me what is this "ionize" term used in this question mean, because I don't know how to proceed?

    3. The attempt at a solution
    I'm thinking "ionize" here means "exciting the atom" and if that is so, Ef - Ei = 2.55eV.
    Also I first found out the energy levels for hydrogen : -13.6eV, -3.4eV, -1.51eV, -0.85eV...

    So I'm thinking that I need to find the correct pair of Ef - Ei that will give 2.55eV so that I can determine the minimum energy level n for the hydrogen atom.

    Please correct me where I'm wrong.
  2. jcsd
  3. Nov 22, 2011 #2
    'excite an atom'.............giving energy to an atom so that an electron makes a transition from one level to a higher level;

    'ionise an atom'.............giving energy to an atom to REMOVE an electron from an atom;
  4. Nov 22, 2011 #3
    Yea, but even then, I'm still not sure how to approach this question. Any hint?
  5. Nov 22, 2011 #4
    You are on the right track except that you need to consider (Ef - Ei) where Ef = 0eV.
    That is you have to find the lowest energy level so that an electron from that energy level, once it gains the 2.55eV, is REMOVED from the atom. Any excess energy appears as KE of this electron.
    Last edited: Nov 22, 2011
  6. Nov 22, 2011 #5
    Oh, so am I right to say that at the energy level, 0eV, the electron will be removed from the atom?

    If this is so, then I understand it as that, the minimum energy level n in this case would be n=3.
  7. Nov 22, 2011 #6
    'Yes' to both quesions.
  8. Nov 22, 2011 #7
    Thank you so much for the explanations! :smile:
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