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Subject: Re: Artificial Horizon.
From: Dr. Geoffrey Kolbe (geof@XXX.XXX)
Date: Tue Apr 02 2002 - 01:41:27 EST
At 13:30 01/04/02 -0500, you wrote:
>
>Geoffrey-
> <As the mirror tilted, the copper strip moved in the
>field of a small rare earth magnet fixed to the sextant frame, and so
>damped the movement.>
>
> Am I the only one here to wonder how this worked? Copper is non-magnetic,
regardless of the magnet you used a simple copper strip would not be
affected by it.
>
As the copper strip moves through the magnetic field, electric currents are
induced to flow in the copper. These electric currents form magnetic fields
of their own such that they oppose the magnetic field from the magnet, so
acting as a brake on the movement of copper strip through the field of the
magnet. Copper is used because it has very low resistance and so this
phenomenon is more efficient in copper. This is basically how electric
dynamos work. Delicate scales are often damped in this way as when the
scales are steady, the magnet has no effect on the scales at all.
A dramatic demonstration of this effect is to place a block of firewood
between the poles of powerful electromagnet and then try and split the log
with a chopper. The harder you try, the further you have to go into the
bushes to find the chopper!
Geoffrey Kolbe.
Border Barrels Ltd., Newcastleton, Roxburghshire, TD9 0SN, Scotland.
Tel. +44 (0)13873 76253 Fax. +44 (0)13873 76214.
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