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Homework Help: Photoelectric Effect question

  1. Dec 11, 2007 #1
    1. The problem statement, all variables and given/known data

    In the photoelectric experiments the photocurrent is proportional to the intensity of the light.Can this result alone be used to distinguish between the classical and quantum theories?
    2. Relevant equations
    3. The attempt at a solution

    As I know, this feature of photoelectric effect is the only feture that is compatible with classical concepts.So,this cannot be used like that...

    [Classical Idea: As you increase the intensity of the light,you are treating the free surface electrons with Electric field and magnetic field of bigger amplitude---Force on them is bigger and they can speed up more promptly giving a bigger value of photoelectric current.]

    Please check the classical idea.
  2. jcsd
  3. Dec 11, 2007 #2
    (I am editing my response, as I misread the question the first time.)

    It is true that the photocurrent would increase with intensity in the classical theory. A greater intensity was supposed to decrease the time lag before the electron was released, thereby allowing more electrons to be set free in a given span of time and increasing the current. This seems to be roughly what your explanation says, though I wouldn't word it quite that way.

    I'm not sure about intensity being exactly proportional to photocurrent in the classical theory, though. I suppose this depends on the mode of absorbing the energy. If the absorbtion rate was proportional to energy, then it would be proportional (since intensity is proportional to energy.)
    Last edited: Dec 11, 2007
  4. Dec 11, 2007 #3


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    Neelakash: Check your classical explanation. An EM wave is made up of an alternating E-field. Why should a larger amplitude in an alternating E-field produce a larger dc current?
    Last edited: Dec 11, 2007
  5. Dec 11, 2007 #4
    Yes, I have edited my response. I hope I did not mislead anyone too badly. :frown:

    The electron was supposed to have a way of gradually absorbing the energy, until at some point the accumulated energy was enough to free it.
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