How the HECK do freakin Magnets work?

  • #1

Main Question or Discussion Point

How the HECK do freakin Magnets work???

I understand that moving electric charges create a magnetic field, but I can't find any explanation that actually describes what is going on, only how to describe what will result of it. ie Maxwell's Equations. Electric charge, and the way they repel each other makes sense. Is there any simple explanation relating the push and pull of charges and how they create a magnetic field?? I read something about special relativity but didn't get it. Please, any response would be appreciated. (Please don't just give me fancy names and equations :))
 

Answers and Replies

  • #2


Well remember how a moving charge would create a magnetic field? Take a swirling coil in which electric current is run through. That solenoid (literally means in greek resembling a pipe, meaning a cylinder) will have a magnetic field which you can imagine by typing solenoid magnet in google and checking out the pictures (butterfly like in 2 dimensional slice). So in this kind of situation you would use the biot-savart law and do the integration (double integral) over all of the cylinder where the current density (moving electric charge) is and get the magnetic field strength. That would be the ampere's law in maxwell's equations. Right. Magnets? That's another story.

Why? Well the thing is that the electrons, the particles that are responsible for natural magnets and are found in every atom making up everything, happen to have a small magnetic field around them constantly. That is related to their spin (search bohr magneton). It so happens that in some materials the electrons decide to prefer a direction on which their spin points to. Spin has a vectorial nature, pointing nature, in a similar way that angular momentum has a vector pointing at the vertical axis to the plane of revolution i.e the axis of revolution hence the word spin by resemblance. The magnetic field of the electron points in the same direction. All these small magnets add up their magnetic fields and you get the macroscopic magnetic field coming out of your ferromagnetic (wiki it) material. Usually the electrons point their spins in a complete random way so you get no magnetic field macroscopically. In the ferromagnetic case they point preferably to one direction, although be careful this doesn't mean that they all point to one direction, let's say when they are not completely random and don't cancel out completely just because of large statistics (lots of electrons) you get a magnet.

The explanation is a bit heuristic but I hope I have helped. If you feel confident enough and you like programming check out the Ising model (wiki it!) it gives a pretty good intuition in what is going on.
 
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  • #3


Thanks for your post. I think I found what I was looking for. I am beginnning to understand how relativity causes moving charges to attract each other. It seems pretty logical to me. I never liked the idea of a "magnetic" force. Now I see that the "magnetic" force is just an easier way of describing the way this works. I wish that every physics textbook said this, though.

Do you know about any sites that talk about electricity, magnetism, elec. waves, etc at more of a freshman level? (without any prior knowledge to complex formulas) I would be very, very happy to find a site that explained things at my knowledge level, but to the depth that I like to know.
 
  • #4
K^2
Science Advisor
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Yes, magnetic force is actually an imbalanced electrostatic force resulting from relativistic length contractions. But dealing with it this way is a bit of a pain mathematically. So introduction of magnetic field is a very convenient way of dealing with things. Especially when you start looking into linear dielectrics and magnetization.

I completely agree that this should be part of the introduction to magnetism, but only as a concept. Mathematics of it does not belong in the basic E&M text.
 
  • #5


When dealing with the relativistic effect causing magnetism, why does moving a magnet in relation to a wire induce a current, but not when you don't, even though the electrons in the magnet are already moving in relation to the wire?
 
  • #6
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The average velocity of electrons in a piece of metal is zero unless some current flows along it. Thus, in a steady wire (relative to the magnet) there are no induced currents
 
  • #7
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Yes, magnetic force is actually an imbalanced electrostatic force resulting from relativistic length contractions.
Is this at all related to the fact that magnetic fields cannot "perform" work on a particle?
 
  • #8


I understand that moving electric charges create a magnetic field
TheTankEngine you should keep in mind that we have absolutely no idea what an electron actually is. We have several frameworks to think of what it does wrt other stuff. If you want a better understanding you should think of all these theories as models that stick because they work. What I tried to point out is that ferromagnetism the model that describes magnets which was your question, has to do with the spin of electrons. That is an intrinsic property of electrons in all important theories, much like their charge. It does not have to do with movement.

Also I do not find the statement that the magnetic force is actually the electric force accurate except if you elaborate a bit on it. The relativistic effect you are referring to is that magnetic force may by modeled as electric force by changing reference frames. That only means that it is more objective to think of magnetic and electric force as the electromagnetic force much in the same way that one should think of space and time as spacetime under relativity. That is, electromagnetism is better modeled when thinking of it as a lorentz quantity say [tex]A^\mu[/tex] that has a norm [tex]A^\mu A_\mu[/tex] that is invariant under inertial reference frame changes (lorentz invariance). [tex]A^\mu[/tex] is taken to be the potentials [tex](\Phi,\vec{A}[/tex]). Having said all this I still don't understand where your knowledge stands in the subject so that I would make suggestions. Please point out on which part of the explanation you do not have a clear picture. A very good starting point is griffith's chapter on relativistic electromagnetism. I no longer have this book but i think it was chapter 10 or something like that.
 
  • #9


As for my knowledge, I don't know ANY equations, hardly any laws, I'm a newb... So, by saying that is a property of "spin" (they should change the name), are you saying that it isn't caused by relativity stuff? I am confused because I don't have any background knowledge (do you recomend any good books? (newb to less newbish.) Something more with these concepts, maybe explaining multiple theories)

Also, how does this tie in with photons and electromagnetic waves?

I realise this is probably too lengthy to explain, so maybe someone can point me to somewhere that I can learn?
 

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