Magnetism

[THEROB]

Can anyone explain to me how magnetism actually works -

In part of a book I read - it claimed that there were loads of electrons all spining the same way and that caused the effect of magnetism. Surely that can't be true as if I had lots of basket balls all spinning the same way nothing would be attracted to them.

Can anyone give me a more indept explaination of how magnetism works.


Thanks

Rob

[Starman]

This one looked interesting:
http://www.wondermagnet.com/dev/magfaq.html#q14

[Guv]

In some sense, this question does not have an answer. If you ask how a mechanical clock works, you can be shown a diagram of the mechanism and be satisfied that you know how the clock works. When you ask how electricity works, you are told that electrons have a negative charge and they flow thorugh conductors, resulting in electric currents. This seems like a satisfactory explanation, but some how I feel that I have a better understanding of the clock.

If you ask why electrons have a charge, you are unlikely to get any answer. If you do get one, I am sure you will not feel that it allows you to understand the phenomena as well as you understand the clock.

I think (not at all sure) that the current theory is that exchange of photons or some other particle results in the magnetic force.

A magnetic field is always associated with a moving electric charge. There is a slight magnetic field around the wire from the socket to a lamp. Every atom has a slight magnetic field associated with the movement of its electrons. Lining the atoms up causes the individual fields to add or reinforce eachother instead of fighting each other. The magnetic fields associated with each atom are alwyas present, even in materials that are never magnetic.

Quantum Theory seems to claim that all forces are due to the intechange of particles between the source of the force and the object acted upon. Due to this claim, there are researchers trying to detect gravitons, which some believe are necessary for gravity to be explained in the same manner as the other three fundamental forces.

This question is a bit like asking how gravity works or why gravity is attractive instead of repulsive. Such questions often do not have have an answer other than "That is the way it is."

BTW: They are not sure about the gravity due to antimatter. Does it attract or repel ordinary matter? Does it attract or repel other antimatter? If they really understood how gravity worked, they would not be wondering about the gravity associated with antimatter. I think it is the same with magnetisim and electricity. We can answer questions about how much force or what direction objects move when acted upon. We can do all sorts of calculations and predict results, but causes are not always clear.

Some unanswered questions lead to deep understandings of physics. Some questions do not have satisfactory answers.

Einstein developed General )not Special) Relativity Theory because he wondered why Inertial and gravitational mass were equivalent. This was an unanswered question of the 19th century.

[jim mcnamara]

Basketballs do not have a net charge, especially when you compare the charge/mass ratio.

Are you talking about Ferromagnetism? Sounds like it.
Try:

http://www.ee.washington.edu/consele...cord/ferro.htm

[THEROB]

Thanks for the replys - it seems that anything that cannot be explained are either given a long name - or in this case are connected to the quantum theory.

[STT]

I believe Quantum Electrodynamics gives us a more detailed explanation about electromagnetism.. also, i believe that they have combined the weak and electromagnetism forces the electro weak force and then combined the strong force with it, now they just need to work on gravity..

Uncertainties in physics lead to deeper questions, but sometimes from these deeper questions new areas of physics arise and these new areas can indirectly answer the initial question. That is why it is vital to keep on thinking about new ideas in physics b/c an entire new theory of physics may arrive from it.. a prime example of this is the Quantum Theory, scientists kept on asking deeper questions until finally Planck suggested that all matter and energy can be absorbed or released in small discrete amounts, called quanta. And from this statement, wave mechanics formed and Shordeger's (spelling?) wave equation was formed which lead to electron configuration which led to how elements bond... Physics is so deep and the only way to unlock the mysteries of the universe is to ask fundemental questions which leads to deeper questions and if your luckly, an entire new theory about how the universe works.

[Guv]

STT reminds me that Planck has always been given credit for inventing or discovering Quantum Theory, but he really did not have a clue about the theory.

Planck explained his experiment in classical terms and actually had some errors in his original paper. Einstein wrote the first papers on Quantum theory, and main stream physicists called him crazy for a year or two due to his ideas about quantized energy.

Planck described his experiment in terms of some type of oscillators within atoms, with different atoms having oscillators that vibrated at different frequencies. Einstein recognized that energy was inherently a quantum phenomena. He described the Planck results as being due to the quantized nature of energy, rather than in terms of atoms containing oscillators analogous to mechanical devices.

Aside from his original paper, I do not think that Planck ever wrote any significant paper on Quantum Theory. His main contributions to physics were classical developments prior to 1900.

BTW: Einstein never got a Nobel prize for General or Special relativity. He got it for some paper on the photoelectric effect, which was a Quantum Theory phenomena, explained in his paper as such. You might wonder why this is so. The reason was to apologize to him for the criticism he received due to his early views on Quantized energy. There was (maybe still is) a tradition that no one could get two Nobel prizes in the same fields (physics, chemistry, et cetera). It was known that even without a Nobel for it, Einstein would go down in history as the driving mind behind Relativity Theory (hardly anybody else contributed). However, without a Nobel for work in Quantum Theory, he could easily be forgotten as one of the most important minds in that field. In addition, he was due an apology for having been called crazy by most mainstream physicists, when he was actually correct in his basic views about quantized energy.

[HarryW]

Originally posted by Guv
A magnetic field is always associated with a moving electric charge.

I'm not sure about this. As far as I am aware, any charged particle, static or otherwise, has an electromagnetic field, just as any particle with mass has a gravitational field. Perhaps I have misinterpreted what you meant.

[STT]

lol thx for the history check Guv, but if i recall, Einstein hated the idea of determining the location or momentum of a particle by probability, so did Plank.. Max had a different idea about his quanta, but Einstein adopted his idea about quanta and solved the mystery of the photoelectric effect using it.. so Planck, by accident, started the Quantum Theory, he was just too blind to see it!

and yea that is pretty ridiculous that Enstein never received a Nobel Prize for his special and general theory of relatively b/c it totally changed the way we think about the universe.. I think the scientists disliked Einstein's theory b/c it lacked postulates.

[HarryW]

'God does not play dice' and all that. That wasn't really the basis of QM though.

[STT]

um... using probability to determine the position of a particle is a huge part of quantum mechanics...

[HarryW]

This whole thread started based on quantum theory. That's not the same issue as probabilistic mechanical processes. It's related but not particularly relevant to the thread.

[kedaman]

Originally posted by HarryW
I'm not sure about this. As far as I am aware, any charged particle, static or otherwise, has an electromagnetic field, just as any particle with mass has a gravitational field. Perhaps I have misinterpreted what you meant.

I think you are confusing electromagnetic field with electric field.
A charge will cause an electromagnetic field proportional to the speed of the reference frame in which the field is measured.
This is probably not a good way to look at it. To visalize
E=v X B
a circular powered circuit will cause a magnetic field go trough it
a straight wire leading charges cause a magnetic field around it.
Same way a
magnet moving forward will cause a electric field around it
rotating magnetic field around a wire causing electricity in it

[Guv]

Kedaman’s post is probably correct, but I only vaguely understand what he is saying.

This subject has gotten to the point where it seems to require more knowledge of charged particles and QED than I have.

Can a charged particle be stationary? If it were stationary, would it cause a magnetic field? Damned if I know the answer to either of these questions.

I think the following statements are valid for classical world objects.

If a magnetic moves relative to a conductor or vice versa, an electric current is induced in the conductor.

If an electric current flows in a conductor, it generates a magnetic field.

The magnetic field of an iron magnet is due to the sum of the magnetic fields generated by moving electrons in individual iron atoms.

The last statement implies that each individual iron atom has a small magnetic field, which may or may not be reinforced by the fields of adjacent atoms. The second statement above seems to imply that the magnetic field in an individual atom is due to electron motion.

[kedaman]

A particle is probably stationary in its own reference frame when no forces or all forces applying on it cancel each other. So even if a straight wire is powered, a point that is moving with the electricity in it will not sense any magnetic force. And yep, the magnetic field caused by the billions of electrons in non aligned(random) atoms will cancel each other, unless they're moving towards a lower potential which would cause them to enforce each other instead in a common magnetic field. A point moving relative to a noncharged object will exprience a magnetic field but unless the speed is extreemly high the force won't be noticable

[THEROB]

When a magnet is brought towards a piece of iron - how does the magnet actually 'reach out and grab the iron'?


Thanks for the replys.


Rob

[kedaman]

The piece of iron will align it's atoms (gets magnetized) so that the magnetic fields reinforce each other and they will attract each other due to magnetic force. This force is similar to Gravity "you just can't explain why, it just the way it is" and thats basically makes it fundamental. Nothing needs an explanation, it needs definition.

[Guv]

Therob: You have asked if anybody can explain how magnetism actually works. I think the answer to this question is No. I really doubt that there is a satisfactory answer to theis and similar questions.

As mentioned in a previous post, current theory talks about forces acting via the exchange of particles. The magnet and the iron exchange particles, which causes the attraction.

The above does not seem like a satisfactory explanation to me, and I doubt that it helps you understand either.

I do not think that there is an explanation which provides a clear understanding of how forces work.

Physicists do a good job with measurements and finding mathematical models that predict what happens to objects acted upon by forces. NASA does a great job of putting satellites in orbit and sending probes to Mars & beyond. Astronomers have detected planets in distant star system.

The equations of gravity provide a wonderful description of what happens. They provide no explanation of how or why. I do not think that any physicist can explain why gravity exists or why it is attractive instead of repulsive.

Some questions do not have satisfactory answers. Questions about how magnetic & gravitational forces actually work seem to be questions without good answers.

[HarryW]

That 'exchange of particles' thing can be a little misleading because the particles (technically called guage bosons) that, according to current theories, carry the electromagnetic force are massless - they are photons.

Actually, now I come to think of it, if photons carry energy then they must have a mass, in keeping with relativistic principles.... err...

Well I'm leaving this thread more confused than I was when I arrived at it now.

[STT]

HarryW, yea mass and energy are interchangeable, so photons should have mass since they carry energy, or maybe I'm not getting the complete story..

CAN SOMEBODY EXPLAIN????

[Parke]

A neutron, a neutral particle, has a magnetic moment associated with it.
Are you trying to understand magnetism from a macroscopic/classical or microscopic/quantum scale?

From a macroscopic viewpoint, Maxwell's equations do an excellent job including the movement of light through a vacuum.

From a microscopic viewpoint, you need quantum electrodynamics and really good math skills e.g. if you try to explain how an electron can have as strong a magnetic field as it does from the viewpoint of a moving charge spinning on the surface of a sphere, the surface of the sphere is moving faster than the speed of light. This is a major problem to physicists as nothing moves faster than the speed of light according to present theory. (As far as I know tachons have not yet been detected.)

Photons carry energy and momentum but they have no mass. Do photons behave as a wave or as a particle? Yes. It depends upon how you are trying to look/study them.

[kedaman]

Originally posted by Guv
Photons have a rest mass of zero, but can never stand still in any frame of reference. I think that any particle with a rest mass of zero must always travel at the velocity of light.

Many particles have a non zero rest mass. In addition to rest mass (if any), a particle has additional mass due to kinetic energy. Perhaps mass-energy is a better term.

I think the energy of a photon is related to its frequency. The higher the frequency, the more energy (mass-energy?).

I am not certain of the above, but believe that the experts make statements similar to the above.

The Energy of a photon is Planck's constant per it's wave length (or by frequency) is quantized "radiation energy"

[HarryW]

Originally posted by Guv
Photons have a rest mass of zero, but can never stand still in any frame of reference. I think that any particle with a rest mass of zero must always travel at the velocity of light.

Many particles have a non zero rest mass. In addition to rest mass (if any), a particle has additional mass due to kinetic energy. Perhaps mass-energy is a better term.

I think the energy of a photon is related to its frequency. The higher the frequency, the more energy (mass-energy?).

I am not certain of the above, but believe that the experts make statements similar to the above.

This sounds about right Guv, thanks for the reminder. It's been a couple of years since I was studying this.

The energy of a photon is indeed related to its frequency, hence the quest for blue lasers a few years ago, and also why there are more red fish in the deep ocean.