Conductive fluids and magnetism

[Getterdog]

I've just started looking into MHD and am a bit confused.ive read the threads on moving charges,and special relativity. So I am thinking of this thought experiment.. we construct a test area shielded from all extraneous magnetic fields, in this area we have a torus shaped pipe and pump a electrolyte solution, around this circle, that is in a small element of this volume ,the charges all balance.as does the whole fluid.so all the charges move with the same velocity. Is a magnetic field generated?

 

[jartsa]

I've just started looking into MHD and am a bit confused.ive read the threads on moving charges,and special relativity. So I am thinking of this thought experiment.. we construct a test area shielded from all extraneous magnetic fields, in this area we have a torus shaped pipe and pump a electrolyte solution, around this circle, that is in a small element of this volume ,the charges all balance.as does the whole fluid.so all the charges move with the same velocity. Is a magnetic field generated?

There would be the large magnetic field produced by the all the electrons, and the large magnetic field produced by all the protons.

Those two magnetic fields would be overlapping very closely, the same way as the electric fields overlap.

Very close to the surface one could measure some electric field and some magnetic fields.

Does the fluid Lorentz-contract? If it does, then charge density increases producing larger E-fields, and current density increases producing larger magnetic fields.

 

[NFuller]

Is a magnetic field generated?

The only magnetic field generated will be from electromagnetic radiation due to the Brownian motion of the charges in the fluid. This isn't very surprising though since all objects at nonzero temperature give off some electromagnetic radiation.

Does the fluid Lorentz-contract? If it does, then charge density increases producing larger E-fields, and current density increases producing larger magnetic fields

I'm not sure how this relates to the problem since the average charge density is zero.

 

[Getterdog]

The only magnetic field generated will be from electromagnetic radiation due to the Brownian motion of the charges in the fluid. This isn't very surprising though since all objects at nonzero temperature give off some electromagnetic radiation.

I'm not sure how this relates to the problem since the average charge density is zero.

There would be the large magnetic field produced by the all the electrons, and the large magnetic field produced by all the protons.

Those two magnetic fields would be overlapping very closely, the same way as the electric fields overlap.

Very close to the surface one could measure some electric field and some magnetic fields.

Does the fluid Lorentz-contract? If it does, then charge density increases producing larger E-fields, and current density increases producing larger magnetic fields.

Well the fluid flow is not relativistic,and the charges balance everywhere, so I would assume these fields would cancel each other ,right?

 

[jartsa]

I'm not sure how this relates to the problem since the average charge density is zero.

What was the problem? Maybe "do objects become magnetic when they move?" Well yes , "no" is quite good answer to that.

This has something to do with MHD, so maybe it would be relevant to consider an experiment were a conducting fluid is moved near a magnet.

The electric current is induced in the fluid. When there is an electric current in the fluid, then the fluid is magnetic.

The magnet had an effect on the fluid even before there was a current in the fluid, so somebody might say that the fluid was magnetic even then.