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Author Topic: Magnets .. again.  (Read 4169 times)

Offline Quantumcat

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Magnets .. again.
« on: 15/11/2003 09:08:06 »
Can someone tell me how magnets work?

Something my teacher told me was baffling, if you cut a magnet at the north end, the cut end becomes a south. If you slice it so that there's only an atom holding it to the other part, the magnet somehow still knows it's attached and stays as North, until you seperate it completely, and the cut end becomes south. Please tell me how they work and how the atoms know that they are still attached and to stay north, and how they know when they are seperated and to become south ...

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« Last Edit: 15/11/2003 09:08:36 by Quantumcat »


 

Offline Ylide

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Re: Magnets .. again.
« Reply #1 on: 15/11/2003 09:30:29 »
Again with the magnets.  ;)  

In an iron magnet, what creates the magnetic field is the alignment of the iron atoms, specifically the spin states of the electrons of the iron atoms.  A magnetized piece of iron has had the atoms polarized so that the domains of the spin states are all (or mostly all) pointing the same direction.   (to do this, they expose the iron to a strong magnetic field, usually the iron is molten and being cooled to solid during the process)  Naturally occuring iron has no net magnetism because the atoms are randomly distributed rather than aligned.  Incidentally, iron is not the only ferromagnetic substance...cobalt, nickel, some other element I can't recall are also capable of ferromagnetism.  (as opposed to paramagnetism and diamagnetism, but I won't confuse you with that right now)

So, if you take a polarized (and hence magnetized) piece of iron and cut it in half, each of those pieces is still polarized becuase the spins of the electrons are still aligned, and hence each is a magnet.  The north and south poles of the magnet are simply indicative of the direction of the flow of the magnetic field lines.  (remember the conversation we had about the potential of energy fields and how the change in potential induces force)  Take a wooden board and draw a bunch of arrows all pointing one direction.  Now cut the board in half.  Do the arrows still point the same way?







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Offline tweener

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Re: Magnets .. again.
« Reply #2 on: 17/11/2003 03:27:46 »
Good explanation cannabinoid!  Another way to say the same thing is that each atom of iron is a tiny magnet with a north and south pole (caused by the way the electrons are held in the atom).  When you put two of the atoms side by side with the same alignment, the fields add together.  When you put several billion of them together, with the same alignment, the fields all add together and they make a strong magnet.  If you cut the bar of aligned atoms (the magnet) in two, each piece is still made of aligned atoms and the poles are still the same orientation.  Each piece generates a weaker field (by 1/2 if you cut it in equal halves), but they still add up the same when together.

If the atoms are aligned randomly, all their individual fields are still there, but they cancel each other out and leave nothing.  In reality, there will be a tiny bit of alignment due to the earth's magnetic field as the iron was formed.  This is how geologists have deduced that the earth's magnetic field has changed polarity in the past.  Some iron ore particles are magnetized the wrong way.

I hope this helps.


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John
 

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Re: Magnets .. again.
« Reply #2 on: 17/11/2003 03:27:46 »

 

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