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What is the meaning of the field about a conventional magnet?

What is the meaning of the field about a conventional magnet? - Physics Forum

What is the meaning of the field about a conventional magnet? - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 08-07-2006, 08:20 PM
Jeff Silverman (Remove the letters in all caps)
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Default What is the meaning of the field about a conventional magnet?



We take a conventional magnet, put a stiff card on top if, pour on some
iron filings and shake gently. The iron filings line up according to
the magnetic "lines of force". School children perform this experiment
and it always impresses the hell out of 'em because the phenomena is so
alien to their experience to this point. Furthermore, we can put a
small compass near a magnet and note which way it points and we get the
same result.

Then, in undergraduate physics classes, we learn that the
electromagnetic force is carried by photons. So far, so good. But what
is the motion or action of the photons that cause the force lines that
we observe?

I suppose that the same question could be asked about two electrical
charges in reasonable proximity but I'm not sure how to run that experiment.


Many thanks,


Jeff Silverman
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  #2  
Old 08-08-2006, 12:12 AM
N:dlzc D:aol T:com \(dlzc\)
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Default What is the meaning of the field about a conventional magnet?

Dear Jeff Silverman:

"Jeff Silverman (Remove the letters in all caps)"
<[Only registered users see links. ]> wrote in message
news:44d7a07b$0$57733$[Only registered users see links. ] ...

*virtual* photons.


It is the action of conveying electro*static* force (aka.
charge). Length contraction/time dilation provide the particular
geometries associated with magnetism.


Look for demonstrations involving pith balls on string.

David A. Smith


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  #3  
Old 08-08-2006, 06:30 PM
PD
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Default What is the meaning of the field about a conventional magnet?


Jeff Silverman (Remove the letters in all caps) wrote:

An excellent question. It's excellent because it points to so many
notions that *sound* plausibly correct but are not. For example, one
might guess that the photons travel in paths that follow the lines of
force. They do not.

So what is going on, then? I'll try to put it in colloquial terms and
as a result will be a little sloppy. Don't make too much of what I say.

In an interaction between a magnet and an iron filing, *lots* of
photons are exchanged. These do a lot of things, but chiefly they cause
jiggling, small perturbations. When things get jiggled, they tend to
settle, and settling really means migrating to a position/orientiation
of lower energy.

What a photon from an orbiting atom does when it encounters an orbiting
electron in another (distant) atom is jiggle it so that the planes of
orientation of the electron orbits tend to line up -- this turns out to
be a position of lower energy. The lines of force tell you essentially
what is the orientiation of minimum energy, for every point in space
surrounding a magnet, and the density of the lines of force tell you
how steep the slope is to get to that orientation if the filing is not
in that orientation.

That's basically all there is to it, in a very very coarse fashion. Now
the quantitative details require more work...

PD

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  #4  
Old 08-09-2006, 06:59 AM
Jeff Silverman (Remove the letters in all caps)
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Default What is the meaning of the field about a conventional magnet?

N:dlzc D:aol T:com (dlzc) wrote:

I think I know what a "virtual" electron or a "virtual" positron is: if
you have a photon rocketing through space, it may spontaneously form an
electron-positron pair, which will collapse on itself and convert back
to a photon. But what is a virtual photon?

I don't understand this answer. If the space/time in the region is
distorted, then why isn't light affected when it travels through the
vacinity of the magnet?

Oh. I supposed you could also do it with two Van De Graff generators.
Duh. Okay, that wasn't a very good question.

Jeff Silverman
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  #5  
Old 08-09-2006, 10:59 AM
pom
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Default What is the meaning of the field about a conventional magnet?

Jeff Silverman (Remove the letters in all caps) a écrit :
Hello,
I really don't know why one has to speak of photons in relation with a
"static" magnetic field.
The famous duality between photons and waves is just that : you have to
have a wave. If the period of your wave tends to infinity, I wonder
about the strange "photon" you will get...
The inter action between a permanent magnet field and the "filings" is
in reality an interaction between a paramagnetic or ferromagnetic VERY
anisotropic particle with a static field
- very difficult to explain without solid state magnetics-
and therefore excludes in some way or the other when an explanation is
given to beginners.
An experiment with a electrostatic field :
In a flat glas container, put some very visquous transparent and
non-conducting fluid (castoroil will work fine), two electrodes of
convenient form and strew some not too finely ground flour over the
surface.
When applying a potential difference of several kV the particles will
align as in the magnetostatic case.
Good luck
pom
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  #6  
Old 08-09-2006, 01:11 PM
N:dlzc D:aol T:com \(dlzc\)
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Default What is the meaning of the field about a conventional magnet?

Dear Jeff Silverman:

"Jeff Silverman (Remove the letters in all caps)"
<[Only registered users see links. ]> wrote in message
news:44D987B7.4050505@STOPSPAMNOW.commercialventva cQ.com...

That is simply "spontaneous pair creation" of real particles.


[Only registered users see links. ]
.... it is a particle that is exchanged between two charges. Many
physicists believe that there are no real photons, simply a very
long series of virtual photons (doing a baton pass).


Since this effect is correlated with "linear" motion, and not
mass, "gravitational lensing" is not an issue. And there are
predicted, very tiny effects on photons passing through very
powerful magnetic fields. Currently being tooled up to see if
the theory works (and I can't remember the name).


And see what effect a magnetic field has on a moving charged pith
ball...

David A. Smith


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  #7  
Old 08-09-2006, 06:15 PM
pom
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Default What is the meaning of the field about a conventional magnet?

N:dlzc D:aol T:com (dlzc) a écrit :
Hmm...
are you sure you meant to reply to me, pom or M. Silverman?
Anyway, your message has only a very slight relation to the original one.
Baffled
POM
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  #8  
Old 08-10-2006, 12:18 AM
N:dlzc D:aol T:com \(dlzc\)
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Default What is the meaning of the field about a conventional magnet?

Dear pom:

"pom" <[Only registered users see links. ]> wrote in message
news:44da2629$0$13514$[Only registered users see links. ].fr...
....

See where I said "Dear Jeff Silverman" above?


Blame it on Thunderbird...

David A. Smith


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