Magnetic Fields: Forming & Understanding Instantaneous Force

In summary: 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.
  • #1
euanos
3
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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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  • #2
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.
 
  • #3
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?
 
  • #4
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.
 
  • #5
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.
 
  • #6
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.
 
  • #7
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.
 
  • #8
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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FAQ: Magnetic Fields: Forming & Understanding Instantaneous Force

What is a magnetic field?

A magnetic field is a region in space where a magnetic force can be detected. It is created by moving electric charges, such as electrons, and is represented by lines of force pointing in the direction of the force.

How are magnetic fields formed?

Magnetic fields are formed when electric charges move, either through a current in a wire or through the motion of electrons in atoms. The alignment of these moving charges creates a magnetic field around the object.

What is the relationship between magnetic fields and forces?

Magnetic fields and forces are closely related. When a charged particle, such as an electron, moves through a magnetic field, it experiences a force perpendicular to both its motion and the direction of the field. This is known as the Lorentz force.

What is instantaneous force?

Instantaneous force is the force that is exerted on an object at a specific moment in time. In the context of magnetic fields, it refers to the force experienced by a charged particle at a specific point in its motion through the field.

How do scientists study and understand magnetic fields?

Scientists use various tools and techniques to study and understand magnetic fields, such as magnetic field mapping and mathematical models. They also conduct experiments, such as the Lorentz force experiment, to observe the effects of magnetic fields on charged particles and further our understanding of them.

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