Can someone explain Gauss' Law for Magnetism

  • #26
dx
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Is it that no one knows the what field lines really are?
We know exactly what field lines are. They are a representation of the corresponding vector field. Maxwell's theory describes the electric and magnetic vector fields, and field lines are just one possible way to visualize these fields.

What I'm driving at is analogous to stating the nature of the strong force is swapping qluons back and forth. To me that's satisfying enough of an explanation for now.
"Swapping gluons back and forth" may give you a satisfying mental image, but this statement is too vague to be an "explanation" of anything.

But there is no such explanation for magnetic force that I've ever heard. What particle mediates the magnetic force?
Thx
Photons.
 
  • #27
Here's an interesting comment from jnorman.
"yango - we truly have no idea how a magnet works, if that is what you are asking. we do not know what a field is, in practical terms, any more than we know how gravity operates. i posted a question here about how a magnet works a few years ago, just to stir people up - you can read what others had to say here:
https://www.physicsforums.com/showthr...hlight=jnorman" [Broken]
 
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  • #28
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Posting something "just to stir people up" is called trolling.

We have a pretty good idea of how a magnet works and what a field is. It's true that, like a five your old, one can answer every explanation with "But, why?" or "What is it really" and eventually get to somewhere where there isn't a good answer. But I am not sure this is a valuable thing to do.
 
  • #29
I'm happy to hear that the fundamentals of magnetism are known. Someone here said magnetism is mediated by photons. So while an electron is coursing thru a circular wire, does it bump into copper atoms and knock off electrons to a higher orbit, then when the coursing electron is sufficiently away from that point does the electron resume it's earlier orbit, thus spewing out a photon (which has no mass) and then what? Does the photon somehow travel to the other pole of the magnet?
 
  • #30
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No, I'm afraid none of that is remotely close to true.
 
  • #31
Vanadium. If you know what is remotely close to true, would you please share it?
Thanks
 
  • #32
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Why don't you take a look at a textbook? Purcell is a good one.
 
  • #33
Is it that complicated to explain in a few sentences?
 
  • #34
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wow, that was a long list to read thru.

I may have some insite, but its probably elementary compaired to what everyone was talking about.

when you have nabla dot B = 0 this is indicating the divergence is zero, or in other words, what goes in comes back out. This is true for any arbitrary surface or volume.

There is no such thing as a magnetic monopole like in electricity (positive or neg charged particles), so only dipoles exist (pairs of sources and sinks). This means the magnetic field wraps around on itself. The field lines have a direction from positive to negative.

Now, what actually makes a magnet work im not too sure. I think its the rotation of atoms and their polarity (when they are all aligned a certain way) hence the term magnetic moment when describing magnetization? Not sure, but this is definitley an interesting topic and thought Id thro in my two cents. Thanks.
 
  • #35
Thanks for that. I understand now, that the divergence is zero and that what goes out comes back in. I think divergence is probably a misnomer. I like 'netfluxthroughput' better. lol Much more descriptive. Divergence seems to imply things separating as a function of time.
So if Nabla dot B = 0, tell me a physical case where Nabla dot (something) =1. This would imply that much enters a volume and nothing ever leaves. Black hole? lol
Nabla dot blackhole=1 Sorry for being flip but I'm exhausted from trying to get a lay explanation for this.
 
  • #36
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an example where the divergence is not zero would be an electrically charged particle.

Say you have a positivley charged atom, this serves as a source of an electric field. The field emits in all directions. put a control volume around this particle and ur divergence is larger than one because you have more coming out then going in. --> nabla dot E = q ; where E = electric field and q = electric charge.

Another example would be the end of a garden hose. When you put a control volume around the end, water is coming out and it is acting as a source. No water is entering the control volume.

Its all really dependent of what you choose your control volume to be and if there are items within the contol volume that cancel out your sources, such as a water drain or a negativley charged particle.

And yes, i think there is speculation that black holes may be magnetic monopoles. this gets into string theory and stuff, but im not too sure about all that.
 
  • #37
Thanks.
 

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