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Electric Charges Scatter Light

  1. Jul 31, 2005 #1
    Reading about the double slit experiment in Six Easy Pieces I came across something I had questions about, which is how they detect whether an electron has gone through one slit or the other:

    "To our electron apparatus we add a very strong light source, placed behind the wall and between the two holes, as shown in Fig. 6-4. We know that electric charges scatter light. So when an electron passes, however it does pass, on its way to the detector, it will scatter some light to our eye, and we can see where the electron goes."


    I am wondering what the explanation is for this effect (the effect being: electric charges scatter light), if it has a name, and if it means that photons have a charge or if the electron is interacting with it electromagnetically, or if something else is going on. Is this actually visible with the naked eye? If so, what does it look like? History? Anyone know who discovered this? Somehow, I've never run across mention of this effect before.

    (I'm asking this effect in and of itself, not in its implications to the double slit, which Feynman covers to my satisfaction.)
  2. jcsd
  3. Jul 31, 2005 #2


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    Example: Compton scattering.

  4. Jul 31, 2005 #3
    Thanks, Zz. Google has a wealth of information now that I know the name of it.
  5. Aug 1, 2005 #4

    Meir Achuz

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    The low energy, long wavelength, scattering of a photon by an electron can be treated classically. It is called "Thomson scattering", and is given in most interemediate UG or grad EM txts.
  6. Aug 1, 2005 #5


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    Yes, I was going to say (to Zoob) that it's a useful thing to have the classical picture in your head. Watch me wave my hands :

    EM wave incident upon charged particle ---> charged particle accelerated by (sinusoidal) Lorentz force ---> oscillating charge radiates in all directions and decays to ground state ---> radiated energy ~ absorbed energy ---> scattering = light absorbed and re-radiated at (nearly) same frequency but different directions
  7. Aug 1, 2005 #6
    Indeed, Meir Achuz, googling "compton scattering" lead me to "Thompson Scattering" and "Rayleigh Scattering". The Thompson scattering seemed most to be describing the scattering mentioned by Feynman, and I was struck by how "classical" all of them were.
  8. Aug 1, 2005 #7
    A nice nutshell version, Gokul.
  9. Aug 4, 2005 #8
    I would add to the above scheme, in the last step, that the scattered wave is born from the interference between the first incoming EM wave (the no absorbed part of it) and the re-radiated wave.

    Best Regards

  10. Aug 4, 2005 #9
    By the way, it's the scattering of light that makes the sky blue and sunsets red, so you can see it. In that case though it is nitrogen and oxygen molecules doing the scattering.

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