The strongest magnet can be produced with an exceedingly
small current, if we only wind sufficient wire upon an iron core. An
electro-magnet excited by a tiny battery of 10 volts, and, say,
one ampere of current, may be able to hold a tremendous weight in
suspension, although the energy consumed amounts to only 10 watts, or
less than 1/75 of a horse power, but the suspended weight produces no
mechanical work. Mechanical work would only be done if we discontinued
the flow of the current, in which case the said weight would drop; if
the distance is sufficiently small, the magnet could, by the application
of the current from the battery, raise the weight again, and if that
operation is repeated many times in a minute, then we could determine
the mechanical work performed. Assuming that the weight raised is 1,000
lb., and that we could make and break the current two hundred times
a minute, then the work done by the falling mass could, under no
circumstances, equal 1/75 of a horse-power, or 440 foot-pounds; that is,
1,000 lb.
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