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I understand the velocity of propagation of a magnetic field is supposed to be c, the velocity of light, but I'm not able to find any experimental tests that this is the case. I believe there have been tests of the velocity of propagation of an electrostatic field, but I'm specifically interested in experimental measurements of the velocity of propagation of a magnetic field.

Thanks.

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    $\begingroup$ You must be mistaken. An electrostatic field is static by definition so it cannot propagate by definition. There is no such thing as a propagating electrostatic or magnetostatic field. There are propagating electromagnetic fields, and there are non propagating electrostatic or magnetostatic fields $\endgroup$ – Dale Oct 22 '18 at 16:54
  • $\begingroup$ Are you saying that, unlike gravity, there is no time-delay between the emergence of a magnetic field, and its affects at a distance? $\endgroup$ – Feynmanfan85 Oct 22 '18 at 17:11
  • $\begingroup$ @Feynmanfan85 No one has said this. If you are talking about "turning on" a magnetic field, then it is not a static field. A static field is a field that is not changing. You could say that your "turned on" field is static in the region of space where it has already propagated to if you wanted. But if you are looking at the field at all space or in a time interval that includes when the field propagates to the region of space you are interested in, then it is not static. $\endgroup$ – Aaron Stevens Oct 22 '18 at 23:12
  • $\begingroup$ @Feynmanfan85 No not at all. I am saying that a static field cannot propagate by definition. The word “static” means that it doesn’t change, so it can’t propagate. $\endgroup$ – Dale Oct 22 '18 at 23:58
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the propagation speed of a suddenly-changing magnetic field in free space is c, the speed of light. Note that since a time-varying magnetic field necessarily creates a time-varying electric field, the thing that propagates away into space from a suddenly-energized coil of wire (for example) will be a wave consisting of a combination of electric and magnetic fields.

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