Magnetic Fields: Forming & Understanding Instantaneous Force

[euanos]

The dramatic lines of force of a magnetic field demonstrated by iron filings in so many introductory texts suggests a problem: A magnetic field is never something that has a process of forming; it is always complete with lines of force: it can change, increase, vanish as in an EM field but never "develops", never partial.

If the lines of force such as those of the Earth's magnetic field do not all close on the earth, as was originally thought, how is it possible that the field is established instantaneously at such intergallactic distances.

 

[Dale]

If the lines of force such as those of the Earth's magnetic field do not all close on the earth, as was originally thought, how is it possible that the field is established instantaneously at such intergallactic distances.

The magnetic field lines are all guaranteed to close by Gauss' law for magnetism.

 

[euanos]

But close on what? The same source, or another source. Does it happen instantaneously? Is there ever a point when the field lines are incomplete?

 

[Dale]

But close on what?

On themselves. All magnetic field lines form closed loops.

Is there ever a point when the field lines are incomplete?

No.

 

[dgOnPhys]

On themselves. All magnetic field lines form closed loops.

...

Hi,

this is not strictly true: magnetic lines can ergodically cover a closed surface, without being themselves closed. See for example magnetic fileds in tokamaks.

 

[pallidin]

Hi,

this is not strictly true: magnetic lines can ergodically cover a closed surface, without being themselves closed. See for example magnetic fileds in tokamaks.

Could you further expound? It seems as if you are ponting towards evidence of monopoles. I do not see that at all in the magnetic fields in tokamaks.
Totally closed loops.
Perhaps I'm wrong.

 

[dgOnPhys]

Could you further expound? It seems as if you are ponting towards evidence of monopoles. I do not see that at all in the magnetic fields in tokamaks.
Totally closed loops.
Perhaps I'm wrong.

No monopoles. When you confine a plasma within a toroid you can end up with magnetic field lines wrapped around a toroidal surface w/o ever closing onto themselves. This is perfectly compatible with B being divergence-free. My basic electromagnetism textbook was written by a professor specializing in plasma physics so this was one of the examples. You can probably google this.

 

[euanos]

Do new lines of force appear over distances at a rate faster than what light is traveling? What is the relationship between those unclosed magnetic field lines around a toroidal surface and magnetic eddys?