Conductive fluids and magnetism

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Discussion Overview

The discussion revolves around the generation of magnetic fields in conductive fluids, particularly in the context of magnetohydrodynamics (MHD). Participants explore thought experiments involving electrolyte solutions and the implications of charge movement and density on magnetic field generation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose a thought experiment involving a torus-shaped pipe filled with an electrolyte solution, questioning whether a magnetic field is generated when charges move with the same velocity.
  • There is mention of large magnetic fields produced by electrons and protons in the fluid, with a suggestion that these fields may overlap similarly to electric fields.
  • One participant suggests that the only magnetic field generated would come from electromagnetic radiation due to Brownian motion of the charges, noting that all objects at nonzero temperature emit electromagnetic radiation.
  • Concerns are raised about the average charge density being zero, leading to uncertainty about how this affects the generation of magnetic fields.
  • Another participant questions whether the fluid experiences Lorentz contraction, which could affect charge density and subsequently influence electric and magnetic fields.
  • There is a discussion about whether the fluid becomes magnetic when an electric current is induced, with some suggesting that the presence of a magnet affects the fluid even before current flows.

Areas of Agreement / Disagreement

Participants express differing views on whether a magnetic field is generated in the described scenario, with some asserting that the fields produced by charges may cancel each other out, while others emphasize the role of electromagnetic radiation and induced currents. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight limitations in their understanding of the relationship between charge density, fluid movement, and magnetic field generation, as well as the implications of relativistic effects on these phenomena.

Getterdog
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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?
 
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Getterdog said:
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.
 
Getterdog said:
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.
jartsa said:
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.
 
NFuller said:
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.
jartsa said:
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?
 
NFuller said:
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.
 

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