I want to add one bit more to Dan Masters' clear explanation to the following
question posed by Warren.Allen@infores.com:
> Here goes: A generator consists of an
> armature (a metal shaft covered with wires) rotating between
> two magnets. There's no physical contact (other than
> brushes). How, therefore, can increased load make the
> armature harder to rotate?
I do not know much about generators in particular, but I am a physicist so I do
know about magnetic fields. The electric polarity of the aramature changes
every time it rotates so that the magnetic field induced by the current also
switches so that it always opposes that of the permanent magnets (in other
words N faces N and S faces S). As the current in the armature increases due
to a load, the magnetic field it creates also increases, requiring greater
force to bring the opposing magnetic poles into proximity. Intuitively, think
of trying to bring the N poles of two magnets together. Even though there is
no physical contact, if you try it again with a stronger magnet, it is going to
require more force. This is why the aramature is harder to turn when it is
required to generate more current.
Richard Breedon
Dept. of Physics, University of California, Davis
'74 TVR 2500M (TR6 engine)
'36 Ford V8
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