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Speed of field ?

  1. Mar 20, 2007 #1
    "speed of field"?

    Is it correct to say that a field (i.e. electric) travels at the speed of light?
    We've been taught that only electromagnetic radiation in a vacuum travels so can we say that the effect of E travels at c also?
    I always thought this to be the case but someone argued that fields are not physical and are 'just there'. Can anyone elaborate please?
  2. jcsd
  3. Mar 20, 2007 #2


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    Staff: Mentor

    It is better to say that changes in a field propagate at some speed. For electric and magnetic fields in a vacuum, that speed is c.
  4. Mar 20, 2007 #3
    ok that makes sense now.
    I was a little confused because when using retarded times, it appears that the potential or field 'influences' at c but it's really because when using retarded times, a charge is moving and therefore the field is changing (and the change propagates at c).
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