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Question: do e/b-fields effect light?

  1. May 9, 2006 #1
    If light is an oscilation in the E and B fields, then, if you sent light thought a capacitor, why doesn't the E-field of the capacitor somehow distort the light? And why doesn't the B-feild of the Earth, or powerlines distort light?

    any insight appriciated.:confused:
  2. jcsd
  3. May 9, 2006 #2

    Claude Bile

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    In a vacuum, there is no distortion, due to the principle of superposition. Inside media however is a different story. Since the response of atoms within a medium is nonlinear to some degree, the principle of superposition does not hold.

    Light can be influenced (Probably a better word than distortion) by an E field inside a medium via either the electro-optic effect or the Kerr effect. The Electro-optic effect is a variation in refractive index with E, thus such an effect can be used to deflect light. The Kerr effect is a similar effect, but has a slightly different dependance on E.

    Light can be influenced by a B field via the magneto-optic effect. An applied B field causes the polarisation of a light beam to rotate as it propagates inside a medium.

    Typically though, for either of these effects to be readily observable, one needs to use hundreds to thousands of volts, or a magnetic field a sizeable fraction of a Tesla.

  4. May 10, 2006 #3


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    Although Claude Bile gave an excellent answer, valid for all everyday situation and more thereon, I would like to add that at extreme intensities modern theory actually predicts that even in vacuum light can be affected by electromagnetic fields.

    Classical electrodynamics obeys Maxwell's equations, which are linear in vacuum, and hence superpostion holds, just like said above. Hence EM-fields cannot interact classically. However, according to Quantum Electrodynamics (QED), there are small non-linear corrections to Maxwell's vacuum equation, allowing EM-fields to interact with each other. That is, QED predicts for instance light-light scattering and light-(E-field) scattering, the later being observed in so called Delbrück scattering (see e.g. G. Jarlskog et al., Phys. Rev. D 8, 3813 (1973)), where light is scattered by the E-field outside a heavy nucleus.
    Anyway, again note that those QED-effects only appear at extreme field strengths.
  5. May 10, 2006 #4
    Interesting. I am very glad to hear that. It seems as you learn more about light, your intuition is always wrong. So I am glad to see that what seems to be true, is actually true even if only at very lage E and B magnitudes.

    Thanks for the responces.
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