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Photoelectric effect and moving from A to B

  1. Jan 8, 2005 #1
    Photoelectric effect and moving from A to B....

    When originally reading about the photoelectric, i guess i was looking at the electrons a bit classically yet using the quantum model of the photon, but it did appear to make sense when concerning the work function. I thought that when it was struck by the photon, the electron gained the photon's energy and thus began to move with kinetic energy equivilent to the photon's energy away from the atom. However, it would still be attracted to the positive ions making up the atom and thus would start to decelerate - if the kinetic energy was not sufficient then the electron would not escape but if it was then it would escape.
    This is what I THOUGHT the work function was - this attractiveness which meant that the kintic energy of the electron would be the energy gained from the photon minus this work function. HOWEVER, I have since been told by my teacher and read in my text book that apparently the electron does not actually travel out of the metal - it simply "appears instantaneously outside its surface with kinetic energy equal to the energy of the phton minus the work funtion". So what actually IS the work function then? It obviously can't be what I thought if the elctron does not actually move out of the metal - there would be no chance for the deceleration I mentioned.

    I also have a second, partially related, question. (though I would prefer my 1st to be address primerily. :biggrin: ) My physics teacher has told me that if I wish to understand how things really work on an atomic level "... ... need to get out of .. [my].. head this stupid idea of things moving from A to B - it doesn't actually happen like that! Electrons in orbitals, atoms as a whole - nothing actually moves from A to B". So what actually happens?! :confused: And why do cars, balls, etc, appear to move like that despite being composed of atoms?

    Thanks in advance. :smile:
     
  2. jcsd
  3. Jan 8, 2005 #2
    The energy of the incident photon (which is localized enough to be considered ONE particle : this was the ingenius quantum-aspect of this theory) is used to eject some electron from an atom. the work function expresses the minimum amout of energy necessary for the ejected electrons to leave the surface. That is the definition. Where the electron comes from is not that important. The reason why there is energy, necessary for leaving the surface is because once the electron is ejected from the atom by the incident photon, other interactions occur between the electron and surrounding atoms. This effect is represented into the work function. But indeed you need to look at it like this : the electron pops up at the surface of the material after the interaction of the photon with the atom (ie the electron-ejection). Then in order for the electron to leave the surface, some amount of energy is necessary (this is the workfunction). The reason for this extra energy are the effects the electron felt when moving to the surface. It is just a way of representing the physical reality

    But indeed in QM, we don't actually look at the electron as being an electron that travels from the place where it got ejected towards the surface (although the workfunction DOES represent that effect)...

    regards
    marlon
     
  4. Jan 8, 2005 #3

    marcus

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    marlon it has been years since i went over this photoelectric effect picture
    and I am no expert (far from it)

    but I tend to suspect that the electron that the photon excites and makes go from surface A to surface B
    is NOT EJECTED FROM AN ATOM
    I tend to suspect that it is a conduction electron that is already up in the conduction band of the metal

    so the work of detaching it from the surface would start at that point, not at the point where and electron is bound in an atom.

    Could this be right? I have no authoritative source handy. perhaps you can tell me.
     
  5. Jan 9, 2005 #4
  6. Jan 9, 2005 #5
    Cheman
    did
    my post not please you ???What is unclear about it ???


    marlon
     
  7. Jan 9, 2005 #6
    I think you need to look at it like this. You certainly have a point here. the probability for this electron to be a conduction electron is higher because less energy is necessary to "eject it". These electrons feel a weaker interaction with the surrounding atomic nuclei and therefore they are quasi-free and delocalized. But it might as well happen with electrons coming from atoms themselves...


    regards
    marlon
     
  8. Jan 9, 2005 #7
    But then again marcus, i wonder is the non-locality of conduction electrons not going to be a problem ???

    Just wondering

    marlon
     
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