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Re: Bar magnets



At 10:25 2/19/01 -0500, John Denker wrote:
[Michael Edmiston]
If the torsion wire is stiff enough to allow a stable
equilibrium for attractive forces, then it is not sensitive enough to yield
a meaningful measurement. If it is weak enough to allow sufficient
sensitivity for a meaningful measurement, you simply cannot attain a stable
equilibrium.
///
b) A needle is added to the end of one arm. Add one to the other arm
for symmetry. The needle goes through a tiny hole. This prevents any
large movements.

In operation, apply whatever electrical force you intend to
measure. Perform a _null measurement_ by rotating the turntable to create
a torsion that just nullifies the force and pulls the needle off the wall
of the cage.

This may cause the needle to snap from one wall to the other, forcing you
to move the turntable back part way to unstick it again. In the worst
case, there is hysteresis

Or to put it more succinctly; the needle WILL snap from one wall of the cage
to the other... there WILL be hysteresis. That is the meaning of unstable
balance.


brian whatcott <inet@intellisys.net> Altus OK
Eureka!