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Electrostatic Speed Experiments?

  1. Dec 25, 2007 #1
    Does anyone know of an experiment that shows that the electrostatic and/or magnetostatic forces have a finite speed, i.e. transmission time? I think I remember reading somewhere that Hertz devised experiments that showed that one or the other or both effects had a finite transmission time.

    In addition, when dealing with a finite propagation speed for these forces, is there a framework separate from special relativity, or should one begin directly from that point of view?
  2. jcsd
  3. Dec 26, 2007 #2


    Staff: Mentor

    Electrostatic or magnetostatic fields are simply the limit of Maxwell's electromagnetic equations where the fields are no longer changing in time. If you are in a situation where the fields are still propagating then they are changing in time and you cannot use the static solutions.

    They propagate at the speed of light. As long as you are doing your analysis in a single reference frame you probably don't need relativity.
  4. Dec 26, 2007 #3


    User Avatar

    the propagation speed of both electostatic and magnetic forces is c, commonly called the "speed of light". for E&M, it really is the very same thing, by definition. but, i think the most common belief about this "c" is that it is not just the speed of the "instantaneous" electromagnetic interaction, but is the speed in nature of all "instantaneous" interactions, including gravity and nuclear interactions.

    so, according to this, no matter what the fundmental interaction is, if something a point A interacts with something else at point B, if a third party that is equidistant from both points A and B can somehow observe a change in amount of "cause" at point A at some time t0 (according to that observer's clock), that observer will observe the "effect" at point B at a later time, at t0 + |locus(A)-locus(B)|/c. doesn't matter what the interaction is, that's how fast it will propagate and no matter what physical interaction someone (or some thing) might use to communicate information from one place to another, that information cannot propagate at a speed faster than c.

    the real physicists may need to correct me, but i think that is the current widely accepted understanding of the speed of any force or interaction.
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