Magnetic Fields: Forming & Understanding Instantaneous Force

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Discussion Overview

The discussion revolves around the nature of magnetic fields, particularly focusing on the formation and characteristics of magnetic field lines, their closure, and the implications of these properties in various contexts, including intergalactic distances and plasma physics. The scope includes theoretical considerations and conceptual clarifications related to electromagnetism.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that magnetic fields are always complete with lines of force and do not "develop" or become partial, raising questions about how fields can be established instantaneously over vast distances.
  • There is a contention regarding whether magnetic field lines close on themselves or on another source, with some arguing that they always form closed loops.
  • Others challenge the idea that all magnetic field lines are closed, citing examples from tokamaks where magnetic lines can cover a closed surface without being closed themselves.
  • One participant suggests that the behavior of magnetic field lines in tokamaks could imply the existence of monopoles, while others disagree, maintaining that the lines are indeed closed loops.
  • A question is raised about the speed at which new lines of force may appear and their relationship to magnetic eddies, indicating further exploration of the topic.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the closure of magnetic field lines and the implications of their behavior in different contexts. The discussion remains unresolved, with no consensus reached on these points.

Contextual Notes

Some claims depend on specific definitions and interpretations of magnetic field behavior, particularly in complex systems like tokamaks. The discussion highlights the need for clarity on assumptions regarding the nature of magnetic fields and their lines.

euanos
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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.
 
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euanos said:
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.
 
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?
 
euanos said:
But close on what?
On themselves. All magnetic field lines form closed loops.

euanos said:
Is there ever a point when the field lines are incomplete?
No.
 
DaleSpam said:
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.
 
dgOnPhys said:
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.
 
pallidin said:
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.
 
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?
 
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