Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Photoelectric effect: a recreative quiz

  1. Feb 27, 2007 #1
    Let us consider the photoelectric effect described on hyperphysics.

    A photon has an energy of 2.25 eV and produces a photoelectron effect on a potassium target,
    the maximum energy of the photoelectron is 0.50 eV,
    indicating the photoelectric threshold of potassium is 1.75 eV.

    Calculating the momentum of the photon and phtoelectron gives:

    momentum photon = 1.2E-27 N.s
    momentum electron = 270E-27 N.s

    The quiz is: what happened to the momentum conservation law?

    Michel
     
    Last edited: Feb 27, 2007
  2. jcsd
  3. Feb 27, 2007 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Nothing.

    1. Photoemission theory has shown that the photon does not impart any significant transverse (in plane parallel to the surface) momentum to the photoelectron. The predominant origin of the transverse momentum is due to the transverse momentum of the electron while it is in the solid.

    2. The photoelectron momentum in the perpendicular direction is due to a combination of (i) the momentum of the photon and (ii)the momentum of the electron while it is in the solid before it was liberated.

    3. The lattice ions are necessary for the photoemission process because they take up the recoil momentum. This means that you cannot get the standard photoemission process from a free electron gas.

    Zz.
     
  4. Feb 27, 2007 #3
    Too bad to ask such a quiz in an expert forum !
    I should have tried an homework forum !

    However, I think it is not necessary to make any reference to the internal structure of the target.
    It is enough to recognize that the target plate can take off a recoil momentum and close the balance.

    But your explanation is more physical !

    Michel
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Photoelectric effect: a recreative quiz
  1. Photoelectric effect (Replies: 3)

  2. Photoelectric effect (Replies: 2)

Loading...