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Homework Help: Photoelectric effect theory (why does this text imply distribution of energies?)

  1. May 6, 2012 #1


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    1. The problem statement, all variables and given/known data
    Consider the experimental results of the photoelectric effect described in Sec. 1.1, i–iv. For each result discuss whether it would be expected on the basis of the classical properties of electromagnetic waves.

    Sec. 1.1(iii):
    For constant frequency and irradiance, the photocurrent decreases with the increase of the retarding potential V, and finally reaches zero when V = –VS.

    The result described in Sec. 1.1, iii shows that there is a distribution in the energies of the emitted electrons. The distribution in itself can, within the framework of the classical theory, be attributed to the varying degrees of binding of electrons to metal, or to the varying amount of energy transferred from the beam to the electrons. But the fact that there exsits a well-defined stopping potential independent of irradiance indicates that the maximum energy of released electrons does not depend on the amount of energy reaching the surface per unit time. Classical theory is unable to account for this.

    2. Relevant equations
    Photoelectric effect theory.

    3. The attempt at a solution
    I read the solution and while I understand most of it, I don't understand how what Sec 1.1(iii) says implies that there is a distribution in the energies of the emitted electrons. By looking at a schematic drawing of the apparatus for studying the photoelectric effect (from my book), it makes sense (assuming I am correct) that the radiant energy would bring a varying amount of energy based on distance differences from the source but I still can't see that from the text in Sec 1.1(iii).

    If I have not given enough information, just ask me to.

    Any help in understanding this would be greatly appreciated!
    Thanks in advance!
  2. jcsd
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