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Query on explanation for electromagnetic field - Feynman lectures on physics

  1. Jan 22, 2012 #1
    In 2-5, an analogy is given for electromagnetic field: two corks in water, and the effect of jiggling one cork on the other (probably the up and down motion).

    Now, that sounded more like water is a medium propagating the energy. But the electromagnetic waves require no medium for propagation, right?

    I know, this is an analogy from the introductory chapters. But am I interpreting this wrong?
  2. jcsd
  3. Jan 22, 2012 #2
    I just started reading the Feynman lectures myself. No, EM radiation requires no medium. What I think Feynman is trying to get across here is that there is a time delay in the reaction of one cork to the motion of the other. This demonstrates that the speed of light (or equivalently, of propagation of changes in an E or B field) is finite.
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