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It is best if you read
the page on the Magnetism
first.
When a current is passed
through a wire which is
suspended in a magnetic
field, the wire will
move.
The direction of
movement is determined
by the direction of the
field and the direction
of the current.
The speed of movement is
determined by the
strength of the field
and the amplitude of the
current.
This principle is used
in the electric motor to
produce rotation.
It is also used in the
loudspeaker where
varying speech currents
through a coil,
suspended in a magnetic
field, causes movement
of a cone, resulting in
sound pressure waves.
The moving coil meter
uses the same idea.
When the meter is
connected to a circuit,
current passes through a
coil. The
coil is suspended in a
magnetic field, and
rotates when current
passes through it. A
pointer fixed to the
coil indicates a value
on a scale.
The Electric Generator
Principle is related.
Here a coil is moved in
a magnetic field.
This induces voltages
and current in the coil.
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