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I Photons and Reflection

  1. Mar 13, 2016 #1
    I was wondering while doing some work on the photoelectric effect about how it is that photons interact with their environment.
    The question that I have is why or how does a massless particle such as a photon reflect of a surface such as a mirror.
    My first thoughts went to collisions with the particles making up the material which the photons are hitting, but wouldn't the material just absorb the energy of the photon leaving no reflection.
    Having no mass how would they bounce, or is it more complex than this.
  2. jcsd
  3. Mar 13, 2016 #2


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    Staff: Mentor

    Photons are not classical particles.

    You can describe the system as absorption and re-emission of photons, but mirrors are so much easier to understand with electromagnetic fields. There is no need to introduce photons.
  4. Mar 13, 2016 #3


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    It is more complex.

    The behavior of photons interacting with matter (including reflection, refraction, and transmission) is covered by the theory of quantum electrodynamics. It is seriously daunting - the required background is such that one is unlikely to encounter it until after completing a four-year undergraduate program. However, Richard Feynman has a written an excellent layman-friendly book: "QED: The strange theory of light and matter" which you might want to try; just be aware that like all popularizations, it is no substitute for the real thing.

    Fortunately most phenomena involving light can be analyzed using classical physics and thinking of light as electromagnetic waves. Photons are only needed when explicitly quantum mechanical effects are involved, as with the photoelectric effect.

    You should also be aware that the word "particle", as used in quantum physics, means something very different than in ordinary English. A photon is not a little moving object that can bounce like a ricocheting bullet, and a beam of light is not a stream of photons flowing by.
  5. Mar 14, 2016 #4
    Ok thanks, this helps a lot.
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