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

Photoelectrics and kinetic energy

  1. Sep 16, 2012 #1
    Hello friends.

    I was just wondering why in photoelectrics, the kinetic energy of an electron released from a certain metal after being struck by a photon follows the classical approach and not the relativistic. For example...

    E_photon = (Planck_const)(frequency) = (Work function) + (1/2)(mass_electron)(u^2)

    instead of

    E_photon = (Planck_const)(frequency) = (Work function) + ((1 - ((u/c)^2)))^(-1)) - 1)(mass_electron)(c^2)

    I've read several texts, including my university's text and Serway's text but the answer isn't really there. Thanks in advance!
    Last edited: Sep 16, 2012
  2. jcsd
  3. Sep 16, 2012 #2


    Staff: Mentor

    AFAIK all the photoelectric experiments that have ever been done have involved highly non-relativistic photoelectrons, so the classical formula works fine, but strictly speaking, it is an approximation and the relativistic formula is the strictly correct one.
  4. Sep 18, 2012 #3
    Cool, thanks Peter.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook