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About the excited state of an electron

  1. Apr 29, 2010 #1
    hi everyone, I'm a beginner in QM and I have a question.

    we know that when an electron is hit by a photon, it gains the photon's energy and goes up to the excited state. Here is my question:

    according to the compton effect, we can interpret the collision of a photon and an electron just like collision of billiard balls, energy and the momentum is conserved. So isn't it important the way the photon hits the electron, so it could slow down or speed up the electron.

    thanks for your help, and sorry for my bad english.
  2. jcsd
  3. Apr 29, 2010 #2
    You must not think of electron as orbiting around proton like planets around the Sun. Instead, think as if electron stays near proton. Or rather, that an electron is a ping-pong ball inside a glass half-filled with water. If you add some water to the glass, a ball will go up, no matter from wich direction you will be adding it. Right?
  4. Apr 29, 2010 #3


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    In Compton scattering, the photon is scattered off the electron, and both the photon and electron still exist after the event. In absorption, the photon is destroyed, and its energy and momentum are absorbed by the atom to drive the electron to a higher bound state. As I understand it, the momentum of the photon is absorbed by the massive nucleus, while the energy goes into driving the electronic transition.
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