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B Photoelectric effect and zero time delay

  1. Feb 20, 2017 #1
    How does the zero time delay between illumination of light and emission of photo electron provides an evidence for the particle nature of light?
  2. jcsd
  3. Feb 20, 2017 #2
    If the photoelectric effect was explained in terms of wave theory.
    Then the energy of wave of incident light will not go to any particular electron but will be distributed to all electrons present on the illuminated surface.
    The time delay would have been much larger than experimental time lag(10^-9 s).
    Whereas particle nature supports the fact that the energy of a single photon entirely goes to single electron, which fits well with our experimental observations.
    Thus it provides us the testimony that radiation posses particle nature
  4. Feb 20, 2017 #3


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    Back in 1905, they didn't know what the structure of matter was. They knew there were electrons, but the nucleus wasn't discovered yet. Classically, an oscillating electric field should exert a force on the electrons. The lack of a time delay means the electrons aren't slowly building up energy to escape the surface. You don't have a situation of a resonant mass and spring where you shake the mass with the right frequency and the displacement builds up until it breaks. It doesn't by itself rule out a classical wave, but together with other observations, it does show that somethign weird is going on.
  5. Feb 21, 2017 #4


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    Yes. The whole energy of the wave would need to have been concentrated in one localised region in order to energise one atom. That's not a very realistic interpretation of the event. Much better described in terms of localised energy packets.
  6. Feb 21, 2017 #5
    Einstein's 1905 paper is very instructive about the thought that lead to establishing that light is quantized. An english translation is available in Stephen Hawking's 2011 book "The Dreams That Stuff Is Made Of".
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