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A couple questions - need answers to for final

  1. Jun 21, 2006 #1
    While studying for my final exam in physics I have come across some problems that I need resolved.

    1) Suppose a the energy required to bring an electron in the ground state of an atom to the second energy level is X J and the energy to bring it to the third is Y J. What happens to a photon that is incident upon this election with ana energy between X and Y?

    2) Similar to the last question...What happens to a photon that does not have enough energy to liberate a photoelectron from a photoelectric surface?
  2. jcsd
  3. Jun 21, 2006 #2


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    -1- I think it depends on the material, but I'm not sure. What have you learned about phonons?

    -2- Seems like it could be reflected or absorbed. Is there more information?
  4. Jun 22, 2006 #3
    2 very interesting questions. Pretty relevant to what I would be tested on also. If you do get the answers do post it here if you don't mind! Thanks!
  5. Jun 22, 2006 #4
    After talking to a few classmates, it appears that if a photon does not have an energy greater than the work function of a metal it is reflected away. I dont agree with this. Couldnt an electron absorb the photon, move to a potential within the metal lower than 0 J, but fall back down to the work function and reemmit the photon?

    I am still curious about the first question. I dont think its answer depends on the atoms.
  6. Jun 22, 2006 #5


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    The photon would simply be unabsorbed. It would go through unaffected (actually, it would interact a bit with the entire atom as a whole, giving it a bit of overall momentum but this is a very small effect for visible or near visible radiation, it's only at very large energies/very small wavelengths that this becomes an important factor as in the Compton effect)
  7. Jun 22, 2006 #6


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    That's what "reflected" means.
  8. Jun 22, 2006 #7
    :rofl: sorry

    Thanks for the help nrqed and StatusX.
  9. Jun 22, 2006 #8
    Is it to say that then the reflected photon has less energy because of this?
  10. Jul 10, 2006 #9
    1) Take note that in order to excite an electron to a higher energy state, there's only one number required, that is the excitation energy and nothing else. For your question, the photon will excite to 1st energy level and the remaining energy becomes its KE. It does not reach 2nd energy level.

    2) By energy conservation, one photon liberates one electron. If there is insufficient energy, the photon simply bounces off the electron. No liberation of electron takes place.
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