Superposition of magnetic fields

[Sha31]

Magnetic fields do not seem to neutralize like electric fields. Magnetic fields always seem to couple without decrease in overall magnitude, so how non-magnetic materials can manage to cancel all the magnetic fields and stay magnetically neutral?

 

To simplify the situation let me rephrase this using 'permanent bar magnets' instead of electrons, and their magnetic dipole moment, as a source for magnetic fields. So, in other words, is there some spatial arrangement of permanent magnets that can neutralize their magnetic fields?

[timo]

Two magnets in the same place with opposite orientation. Alternatively, two magnets with opposite orientation close to another and then seen from a large distance. That sounds like "no" but it's the same "no" as for electric fields. For real materials, things might be a bit more complex because "close" then is the typical distance between atoms where matter usually behaves a bit differently than on the meter scale.

[Sha31]

Two magnets in the same place with opposite orientation. Alternatively' date=' two magnets with opposite orientation close to another and then seen from a large distance.

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I'm afraid magnetic fields do not cancel in either case. Large distance has nothing to with this, the point is to neutralize magnetic fields immediately around the composition, where it can be measured. Opposite magnetic poles stick to each other, actually increasing the magnitude, so two magnets couple to make one stronger magnet.

 

 

That sounds like "no" but it's the same "no" as for electric fields. For real materials, things might be a bit more complex because "close" then is the typical distance between atoms where matter usually behaves a bit differently than on the meter scale.

 

For electric fields to neutralize all you have to have is uniform (random) distribution. 10 protons and 10 electrons will pair in 10 electric dipoles known as hydrogen atoms and each will be neutral on average making the area they occupy electrically neutral, unlike magnetic dipoles.

 

 

Permanent magnets have this uniform distribution of electrons where electric fields neutralize and obviously their magnetic fields do not. Magnetic fields of electrons actually couple and the larger the magnet the stronger net magnetic field will be.

[swansont]

I'm afraid magnetic fields do not cancel in either case. Large distance has nothing to with this, the point is to neutralize magnetic fields immediately around the composition, where it can be measured. Opposite magnetic poles stick to each other, actually increasing the magnitude, so two magnets couple to make one stronger magnet.

 

Helium-4 has a nuclear magnetic moment of zero, so your claim is clearly false.

 

For electric fields to neutralize all you have to have is uniform (random) distribution. 10 protons and 10 electrons will pair in 10 electric dipoles known as hydrogen atoms and each will be neutral on average making the area they occupy electrically neutral, unlike magnetic dipoles.

 

The electric field outside the atom is zero, but what about inside? And you just said that far-field effects don't count.

[Sha31]

Helium-4 has a nuclear magnetic moment of zero' date=' so your claim is clearly false.

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We were talking about bar magnets, macroscopic objects and static solution. Timo said two magnets with opposite orientation close to another will neutralize each other, so I said they will actually couple to make one stronger magnet, is this what you refer to as "false claim"? Anyhow, do you know what is the spatial arrangement and orientation of magnetic moments of those particles in Helium-4 that makes it magnetically neutral? Is hydrogen magnetically neutral as well?

 

 

The electric field outside the atom is zero, but what about inside? And you just said that far-field effects don't count.

 

Not inside, but outside, as combined entity (on average). Like molecules of water, which are electric dipoles, yet they still arrange into combined electrically neutral entity, say 'glass of water', that's what I mean. When you take a piece of wood and when it does not interact with magnet, you say it's magnetically neutral, that's what I mean. So, is there some static spatial arrangement of permanent bar magnets that can neutralize magnetic fields around them, make them magnetically neutral as a whole?

Edited December 27, 2009 by Sha31

[swansont]

We were talking about bar magnets, macroscopic objects and static solution. Timo said two magnets with opposite orientation close to another will neutralize each other, so I said they will actually couple to make one stronger magnet, is this what you refer to as "false claim"? Anyhow, do you know what is the spatial arrangement and orientation of magnetic moments of those particles in Helium-4 that makes it magnetically neutral? Is hydrogen magnetically neutral as well?

 

The Pauli exclusion principle tells me the spins will be anti-aligned for both the protons and the neutrons. They have a magnetic moment, so they are magnets.

 

And no, you claimed it for magnets in general, and used macroscopic magnets as an example. That's all it is — a claim. You have provided no evidence to back it up. Timo was right.

 

Not inside, but outside, as combined entity (on average). Like molecules of water, which are electric dipoles, yet they still arrange into combined electrically neutral entity, say 'glass of water', that's what I mean. When you take a piece of wood and when it does not interact with magnet, you say it's magnetically neutral, that's what I mean. So, is there some static spatial arrangement of permanent bar magnets that can neutralize magnetic fields around them, make them magnetically neutral as a whole?

 

You are describing two different situations. Something that does not generate a magnetic field may still respond to a magnet. Take your own example , water: it has no net electric field, but the molecules will react to an electric field. It's a fairly simple classroom demonstration to deflect a stream of water with a static charge.

 

So which situation do you want? No field, or not reacting to an external field? Even a ferromagnet, above its Curie temperature, will have no field.