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Photoelectric Effect and light as a particle

  1. Aug 5, 2009 #1
    I have a question, why does light act like a particle during the Photoelectric Effect Experiment, but acts as a wave in Thomas Young's Double Slit Experiment? Does anyone have a good book that I could rent in the Library or find on Questia.com or find online that I could use to read up on this?
  2. jcsd
  3. Aug 5, 2009 #2


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    Do you mean why does the photoelectric effect show that light is a particle?
    For the photon to eject an electron there must be enough energy in a single photon - you can't use lots and lots of lower energy ones.
    This proves that photons are discrete.

    The wave part is more interesting. Photons don't behave like waves - everything does! Even elephants defract through a slit. But the wavelength decreases with increasing momentum so it's only noticable with very low momentum particles such as massless photons or low mass particles like electrons
    It's called the de Broglie wavelength
  4. Aug 5, 2009 #3
    Yes, I meant why the photoelectric effect shows that light is a particle? I have to write a 4,000 word paper on whether light is a particle or wave, and I have the "waviness" (DeBroglie Hypothesis/Wavelength). I need a work though that explains in greater detail about the photoelectric effect.
  5. Aug 5, 2009 #4
    Last edited by a moderator: Apr 24, 2017
  6. Aug 5, 2009 #5
    Last edited by a moderator: Apr 24, 2017
  7. Aug 6, 2009 #6
    Thanks for your guy's help, those look like good/solid references for my paper. And Phrack, I thank you personally because I was looking for that but couldn't find it.

    I found a site on how to conduct a cheap $100 photoelectric experiment (with LED's) and my teacher has all the materials for Young's Double Slit Experiment. Right now I just have to make an outline and an annotated Bibliography (haven't done any of the labs yet) before school starts on Aug. 25.

    Does anyone know what I could put in it? This is what I have so far (it's in no specific order and the sources that you guys gave me are not added yet because I have to go tutor):
    Question that I have to answer: Is light a particle or wave and what effects it and why?

    • Thomas Young’s Double Slit Experiment
    o http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l3d.html [Broken]

    • Photoelectric Effect Experiment

    • De Broglie Hypothesis
    o De Broglie Wavelength

    • Explination of Photoelectric Effect
    o Why it acts as a particle
     Photons and threshold freqency
     “The photoelectric effect is the emission of photoelectrons from a clean metal surface due to incident light whose frequency is greater than a threshold frequency. The photoelectric effect supports the particle theory of light because it shows that the energy required to release electrons from a metal is totally dependent upon the frequency of the light, and not the intensity. Therefore, certain frequencies of light, no matter how intense, cannot cause an electron to be emitted from the surface of a metal”

    • Wave-Particle Duality
    o http://physics.about.com/od/lightoptics/a/waveparticle.htm

    • Background Information
    o http://physics.weber.edu/carroll/honors-time/duality.htm
    Last edited by a moderator: May 4, 2017
  8. Aug 6, 2009 #7
    I'd read your paper once you finish and referenced it on the physics forum. Though I'm not sure you are allowed, personally, to link to your own material per PF rules.
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