meredith lamb wrote:

> Hi all,
>
> A Interesting question (too me), has arisen while briefly
> utilizing some neodymium magnet disks.  The normal coil/
> magnet scheme for seismometers is to use North-South
> poles facing each other; with the coil inbetween.  OK....
> what if same poles are repelling (~ North-North); with the
> coil inbetween.  Is there really any difference?  Is the normal
> attraction of unlike poles really better than the repelling
> variety?

If two identical magnets are placed with north poles facing,  there is
theoretically no voltage produced in
a coil which is placed in the center between them.  That is, the coil sees
flux in one direction from one
magnet, and identical flux in the opposite direction from the other.  Thus
the two voltages cancel out.
Try the experiment with the magnets in the same and opposite directions.
Move any coil with a good number of turns in the center of the gap, and
measure the voltage with a simple voltmeter (or better on an
oscilloscope).  The ones with north to south will give much larger voltage.

George Harris


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