magnetic field

Hi,
I would like to know what is a magnetic field. I mean what is it composed
of.
I searched google , asked people around me , no one seems to know.
Obviously everyone knows where how, but not what.
I thought it was electrons, but that cant be.
thank you
ken
Reply to
Ken
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A magnetic field is part of a theory we use to describe the interaction between charged particles, which are themselves just part of the theory.
At the end of the day, science only ever describes. It never explains things except in terms of other descriptions. By asking what a magnetic field is out in the real world, you're asking for something that is beyond the scope of measurement, and therefore unknowable even in principle.
Sylvia.
Reply to
Sylvia Else
Try quantum physics.
Ken wrote:
A magnetic field is part of a theory we use to describe the interaction between charged particles, which are themselves just part of the theory.
At the end of the day, science only ever describes. It never explains things except in terms of other descriptions. By asking what a magnetic field is out in the real world, you're asking for something that is beyond the scope of measurement, and therefore unknowable even in principle.
Sylvia.
Reply to
Brian
look at this one
formatting link
search word in google is: emf
Reply to
Ryan Wheeler
A field is a region of influence- hence a magnetic field is a region of magnetic influence- i.e. there are effects due to the magnetism. Beyond that one gets into "what is magnetism"
Reply to
Don Kelly
Basically, both electric and magnetic fields store electromagnetic enegy. Electric fields can be created by something as simple as a battery, and magnetic fields come from magnets or from electrical coils while a current flows. Why magnets make magnetic fields is a question for quantum physics.
With respect to Sylvia, James Clerk Maxwell expressed a relationship between electric and magnetic fields in the mid 1800's. Maxwell's contribution was to show that a magnetic field is created as an electric field changes, and an electric field is created as a magnetic field changes. The result is that if I switch an electric field off and on, I get a magnetic field that swells and collapses with each on-off transistion.
If I flip the swith fast enough at some frequency, I will find that the magnetic field comes and goes with the same frequency. But, since a changing magnetic field will create its own electric field, the effect moves out to this new field, which makes another magnetic field, and so on, and that is radio.
Kevin
Reply to
Kevin Kilzer
I'm not disagreeing with Kevin, but there is a simple thought experiment that shows how careful one must be about taking a theory, such as that of James Clerk Maxwell, and attempting to use it as anything more than a description.
Take two electrons, separated in space, stationary relative to some observer. There's an electric field, obviously, but no magnetic field. Now take another observer moving perpendicularly to the line joining the electrons. This observe sees the electrons in motion. Electrons in motion are an electric current, and an electric current produces a magnetic field, so for that observer there is a magnetic field present.
So one observer finds a magnetic field present where another observer finds none. The notion that a magnetic field has a concrete existence is clearly problematic. This paradox doesn't appear in the theory itself, because it simply tells you what will happen (or more exactly, what your measurements will show). It doesn't say anything about what is "really" there.
Sylvia.
Reply to
Sylvia Else
i was pretty sure that the magnetic field was the horizontal plane where alnico, samarium cobalt, and neodymium magnets were stored prior to instillation in speakers and microphones.
but after some consideration i decided it must be a nickname for 3M stadium.
perhaps its just a wild gauss chase but i wouldn't get too fluxed up over it.
Reply to
TimPerry
This is all a bit over my head, but presumably the first observer (the one who doesn't see the magnetic field because it doesn't exist for him) sees something else; whatever the second observer sees as a magnetic field manifests itself somehow for the first observer? Don't conservation laws say that elements might vary, but the total sum must be the same? Probably not...
Reply to
John
in article snipped-for-privacy@4ax.com, Kevin Kilzer at snipped-for-privacy@mindspring.com wrote on 9/26/04 7:59 PM:
Whatever a magnetic field may be, quantum physics is not going to explain it. Quantum physics will merely use the magnetic field as part of the hamiltonian in a quantum equation such as the Schrödinger equation. From that, quantum consequences of magnetic field will be derived but not explained.
Bill
Reply to
Repeating Rifle
in article 4157853f$0$20129$ snipped-for-privacy@news.optusnet.com.au, Sylvia Else at snipped-for-privacy@not.at.this.address wrote on 9/26/04 8:13 PM:
Think special theory of relativity and Lorentz transformation. Realize that both electric field and magnetic field are part of a tensor, that is relatavisticly invariant.
What is a tensor you my ask. Rather than giving a circular argument I will present *stress* as an example. Inside a stressed medium there will be a combination of tensile and shear stresses. This combination is an entity by itself, in which tensile and shear stresses cannot be separated out. If you carefully twist a piece of blackboard chalk (if it still is available) without bending it, it will break with a 45 degree break. Even though you are applying rotational shear alone, there are directions, at 45 degrees to the shear where tension is produced. The chalk is weaker in tension than in shear and the tension ends up causing the break. Stress is a tensor that is an entity where where shear and tension are not independently present.
The same is true for electric and magnetic fields. The entity is a tensor that mixes electric and magnetic fields.
Bill
I
Reply to
Repeating Rifle
in article RAM5d.5110$ snipped-for-privacy@news01.roc.ny, John at snipped-for-privacy@john.com wrote on 9/26/04 9:23 PM:
Whatever one observer sees is what another observer sees when transformed ty the appropriate Lorentz transformation.
Bill
Reply to
Repeating Rifle
On Mon, 27 Sep 2004 13:13:03 +1000, Sylvia Else put forth the notion that...
I think Heisenberg first developed that theory, but I'm not certain.
Reply to
Checkmate
will
entity by
Shear stress can always be seperated out: you can represent any combination of shear and tensile stress as pure tensile stress (google for Mohr's Circle).
The Mohr's Circle operation is just a graphical way of diagonalizing the stress matrix (well, it only works in 2D where the tensor is of rank 2).
-Ed
Reply to
E. Rosten
It isn't really composed of anything. It's a region in which a magnetic force can be detected. Ever seen a police car on the motorway? Everyone within 100 yards drives exactly at the speed limit. the police call this a bubble or zone of legality. The zone isn't composed of anythig but you can "feel the force".
Reply to
CWatters
Hi Sylvia,
Just a little note here, in your post the observer is moving relative to the electrons not the electrons relative to each other so there is no change in the electric potentials, unless the observer is at a different electrical potential themselves, of course then they are not a 'neutral observer" so the stationary observer would then see the field created as the other non stationary observer moved past the stationary electrons. The question I come up with is exactly what does the "at differential" moving observer see, since they are part of the emf/cemf event.
Matt
Reply to
softh
in article cj8eqs$9kd$ snipped-for-privacy@pita.alt.net, Checkmate at snipped-for-privacy@The.Edge wrote on 9/27/04 12:15 AM:
Planck introduce the concept of a quantum of energy in order to explain the spectral distribution of black body radiation. Einstein and others were able to extend the concept to explain specific heat and photoemission. Bohr first applied it to atomic physics. Heisenberg developed the first modern theory of quantum mechanics. Shrödinger formulated a wave equation that was much more familiar to physicists of the day. The big surprise was that the Schrödinger formulation gave identical results to that of Heisenberg's in spite of appearing to be very different. The Schrödinger formulation was much easier for making calculations while the Heisenberg formulation was better suited to understanding essence of what quantum physics was all about.
Bill
Reply to
Repeating Rifle
in article snipped-for-privacy@my.sig, E. Rosten at snipped-for-privacy@my.sig wrote on 9/27/04 2:31 AM:
Mohr's circle is a tensor on the cheap. In a sense, it was developed for engineers who were not formally trained in tensors or their matrix representations. The days when that was necessary, I hope, are over.
Another crutch for tensors was developed under the name of *dyadics*.
Another example of tensor quantities is that of the dielectric constant tensor. Displacement (D field) is not in the direction of the electric field (E field) for an anisoptripic material like a crystal.
Even more complicated are the piezo-elasto-optic tensors used for electro-optic devices where there are simultaneous stresses and optical index changes.
Bill
Reply to
Repeating Rifle
| |> |> Take two electrons, separated in space, stationary relative to some |> observer. There's an electric field, obviously, but no magnetic field. |> Now take another observer moving perpendicularly to the line joining the |> electrons. This observe sees the electrons in motion. Electrons in |> motion are an electric current, and an electric current produces a |> magnetic field, so for that observer there is a magnetic field present. |> |> So one observer finds a magnetic field present where another observer |> finds none. The notion that a magnetic field has a concrete existence is |> clearly problematic. This paradox doesn't appear in the theory itself, |> because it simply tells you what will happen (or more exactly, what your |> measurements will show). It doesn't say anything about what is "really" |> there. |> | This is all a bit over my head, but presumably the first observer (the one | who doesn't see the magnetic field because it doesn't exist for him) sees | something else; whatever the second observer sees as a magnetic field | manifests itself somehow for the first observer? Don't conservation laws | say that elements might vary, but the total sum must be the same? | Probably not...
If there is motion between the observer and the electrons, the observer might THINK he sees a magnetic field. But is it really there? That lies in the ability to observe. How do you tell if a magnetic field is there or not? You measure it by seeing how it acts on something. One way is with a coil and ampmeter. But now that's electrons again. The net effect is that something which is electrically changed has ultimately caused an electrical current where movement is involved.
On the other hand, how do we know there is an electron there? Maybe it only looks like it because that would explain a magnetic field, which is what we are measuring. Maybe what we sense as an electric/static charge is really a sensation of a magnetic current because we have to move in some way to know there is a charge and where it is.
One cannot be without the other, but the real question is whether there are really two things or not. I suggest that the answer is that what is really there is one thing that simply is characterizsed both ways.
Reply to
phil-news-nospam
| It isn't really composed of anything. It's a region in which a magnetic | force can be detected. Ever seen a police car on the motorway? Everyone | within 100 yards drives exactly at the speed limit. the police call this a | bubble or zone of legality. The zone isn't composed of anythig but you can | "feel the force".
It is composed of something called "fear".
Reply to
phil-news-nospam

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