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PICList Thread
'[OT] MAGNETIC FIELDS'
1999\09\26@094223 by Donald L Burdette

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On Sun, 26 Sep 1999 00:06:51 -0400 Brian Kraut wrote:

>Is it theoretically possible to have a spherical magnet that
>has the north pole on the outside and south on the inside?

Though I'm no expert, I think the answer is yes and no (sounds like an
expert answer, doesn't it?)

Yes - you could complete your ping-pong ball with all the north poles on
the outside and all the south poles on the inside.  In the theoretical
case you could do this perfectly well and achieve exactly what you
requested.

No - this would no longer be a magnet.  Let me explain what I mean,
because what I said may not be quite true in the most literal sense.  A
magnet (my definition) is an object that creates a magnetic field.  This
field is often described by 'lines of flux' which travel through space
from one pole (let's say north) of the magnet to the other (south).
Maxwell's equations require that these lines actually be closed loops,
and this happens because the lines travel through the magnet from south
to north to close the loop.  For your sphere, any flux lines going out of
the sphere (north) must also come back into the sphere in order to reach
the south pole.  Spherical symmetry requires that the flux density be the
same at all points on the sphere.  Since the 'out' and 'in' must total
the same, and must be uniform, the only possible answer is that they
cancel completely.  This argument holds true at any point on a sphere
centered at the center of your magnet, with any radius.  Since that
includes all the known universe, your magnet does not meet my definition
at any point in the known universe!

Can anyone see a flaw in my logic?

Don

'Perpetual motion is impossible, but it perpetually moves people to try.'

1999\09\26@104557 by Wagner Lipnharski

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If you really want to play with magnets, first save away all your
computer diskettes, then go to a electronic repair shop and buy for
cents some of the surplus (bad, replaced) Microwave oven MAGNETRON
valves, dismount the metallic case and you will find one or two very
(really) powerful circular magnet (axial polarization), and prepare to
have a lot of trouble to separate them if you put two together. If you
instal a non magnetizable rod inside them (N-S S-N configuration) in a
vertical position, the top will float easily and will stand several
ounces of weight easily.  You can do several experiments with coils and
voice-coils with those strong magnets... use your PIC to generate the
power patterns...
Wagner.

1999\09\26@132353 by Mike Keitz

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On Sun, 26 Sep 1999 10:35:47 -0400 Wagner Lipnharski
<spam_OUTwagnerlTakeThisOuTspamEARTHLINK.NET> writes:
> If you really want to play with magnets, first save away all your
> computer diskettes, then go to a electronic repair shop and buy for
> cents some of the surplus (bad, replaced) Microwave oven MAGNETRON
> valves, dismount the metallic case and you will find one or two very
> (really) powerful circular magnet (axial polarization),

These magnets are really powerful.  Much better than the ones typically
found in loudspeakers.

Of course if you're like me you've played with the magents a little but
are now wondering what's inside the rest of the magnetron.  Here you must
be careful that the ceramic seals of the magnetron (which you'd need to
break to see inside) are not made of toxic BeO.  I kind of doubt it would
be used in a consumer device (except an early model when the magnetron
was really expensive) but if you aren't sure it would be best to throw
away the "heart" of the magnetron without dismantling it further.

and prepare
> to
> have a lot of trouble to separate them if you put two together.

They are made of rather brittle ceramic.  Don't let them crash into each
other or into ferrous metal surfaces as they probably will break.

Even more powerful, though small, magnets can be found in hard disk
drives which are new enough to use a voice coil instead of a step motor
to move the head.  The magnets are found inside the disk cover,
suprisingly close to the disk, on the back end of the arm that holds the
heads.



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1999\09\26@140143 by Steve Kelley

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<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>Even more fun . . . . .
although small , the * Rare- Earth * magnets are available at</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>* Junk - Shack * ( a.k.a.
Radio- Shack ) that are the Cobalt type.</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>These will prove that even
materials that we consider non-magnetic are subject</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>to their fields . . . for
instance . . . . take a piece ( sheet ) of brass and tilt it at a 45
degree</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>angle.&nbsp; Let one of
these slide down the sheet and you'll notice that it produces * Eddy *
</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>currents that are strong
enough to cause an attraction to the brass .</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2>Oh . . . . almost forgot .
. . .&nbsp; .you can use them to erase your PIC&nbsp; : )</FONT></DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif" size=2></FONT>&nbsp;</DIV>
<DIV><FONT color=#0000ff face="MS Sans Serif"
size=2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Steve</FONT></DIV>
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   <DIV><FONT face=Arial size=2><B>{Original Message removed}

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