Can magnetic field exist without electric field?

[Dale]

Classically you can certainly have an electric field without a magnetic field or a magnetic field without an electric field. On the quantum level, since all fundamental charged particles also have spin you cannot have either without the other.

In either case the answer to the question is the same for the magnetic field as it is for the electric field, but the answer differs between classical and quantum EM.

 

[Orodruin]

Classically you can certainly have an electric field without a magnetic field or a magnetic field without an electric field. On the quantum level, since all fundamental charged particles also have spin you cannot have either without the other.

It is possible also for neutral particles to have a non-zero magnetic moment. Of course, if you are moving relative to such a particle an electric field still appears ...

Does it really make sense to talk about electric and magnetic fields on the quantum level other than as a semi-classical approximation?

 

[Jabbu]

It is possible also for neutral particles to have a non-zero magnetic moment. Of course, if you are moving relative to such a particle an electric field still appears ...

I don't think we would call them neutrons if they could acquire electric fields every time something is moving somewhere.

 

[Orodruin]

Just as moving charges give you magnetic fields, anything giving rise to a magnetic field that moves is going to give you an electric one. This is due to how the electromagnetic field transforms under Lorentz transformations. The divergence of the electric field from the moving magnetic source would still be zero and so also the charge density.

 

[Thierry]

Under static conditions, either can exist w/o the other. A superconducting loop w/ a steady dc current has magnetic field, but no electric field. The counterpart of this setup is a charged capacitor open circuited, as there is an electric field w/o a magnetic field.

Again these are static conditions, i.e. not changing with respect to time. Under dynamic conditions, i.e. changing wrt time, neither can exist w/o the other. If one field is time-changing, the other must be non-zero.

Claude

What about transformer cores? the magnetic field oscillates at 50 hz but there's no electric field in a metal. There's eddy currents but no electric field, or am I missing something?

 

[cabraham]

What about transformer cores? the magnetic field oscillates at 50 hz but there's no electric field in a metal. There's eddy currents but no electric field, or am I missing something?

Yes there certainly are eddy currents in the core metal. But why would you conclude that there is 0 electric field? Core metal is conductive with value $\sigma$, eddy current density has value $J$, and remembering Ohm's law in 3 dimensions: $J=\sigma E$, so that $E=J/\sigma$.

Does that help? Best regards.

Claude

 

[jtbell]

there's no electric field in a metal

...under electrostatic conditions.

 

[Thierry]

Yes there certainly are eddy currents in the core metal. But why would you conclude that there is 0 electric field? Core metal is conductive with value $\sigma$, eddy current density has value $J$, and remembering Ohm's law in 3 dimensions: $J=\sigma E$, so that $E=J/\sigma$.

Does that help? Best regards.

Claude

ah yes, it does. Thanks!

 

[Thierry]

...under electrostatic conditions.

I see. of course, thanks!