I know what is an electric field. It exerts a force over distance between electric charged particles.

I know what is a magnetic field. It exerts a force over distance between particles with magnetic dipole moments.

I don't know how to show the interaction over distance between EM radiation and what? The absorption of a photon by an electron hardly one can call a force over distance. Maybe the expression EM field is a comprehensive term for electric and for magnetic fields? The claimed EM field in QM seems not to be a field in the meaning of influence nor force of what's ever.


There is no 'the electric field' and 'the magnetic field' separate of each other. Yes, we discuss these things as independent in introductory treatments, but that is a pedagogical choice.

There is only the electromagnetic field which comprises both effects and can be described by a skew-symmetric Lorentz tensor of the 2nd rank. This implies that the particular combination of electric and magnetic components observed from a field are altered by the relative velocity of source(s) and observers which is why we can't make a strong distinction between the two classes of fields even though their effects can be easily separated in a teaching laboratory.

  • $\begingroup$ Are you saying there is a magnetic field even around a static electric field? $\endgroup$ – user16307 Oct 22 '17 at 19:22
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    $\begingroup$ For some observers it may have zero magnitude, but observers moving with respect to them will disagree. The theory of electromagnetism is inherently relativistic. $\endgroup$ – dmckee Oct 22 '17 at 19:25
  • $\begingroup$ Very interesting. Are you saying, the observer in motion relative to the static charge will report a magnetic field; but the observer in the same frame with the static charge who does not move relative to the charge will not report any magnetic field? Is there any experiment you have encountered nicely presents this? Or thought experiment. $\endgroup$ – user16307 Oct 22 '17 at 19:35
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    $\begingroup$ Every example of Ampere's law is a test of the idea: currents are charges in motion. SO charge up a pith-ball and note that it does not affect a compass then pass a current through a wire and note that it does. $\endgroup$ – dmckee Oct 22 '17 at 20:02

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