If you take a Magnet and move it relative to
a Conductor, a current is made to flow in that conductor.
The magnitude of that Current is dependent on many things,
including the Magnetic Flux density cutting the wire; the
relative Speed of the Magnet; the number of turns the
conductor makes, etc. It can be said that the Moving Flux
lines "cutting" the conductor's path induces an Electro
Motive Force, an "E.M.F."
Conversely, if an electrical Current is
passed through a Conductor, a Magnetic Field (Flux Lines)
forms around the Conductor. With a sufficient number of
turns of wire one has an Electro Magnet. If
one were to place two Conductors side by side; one passing a
steady Electric Current; the other wire is unaffected.
Although there are Magnetic Flux lines "cutting" the second
Conductor, No E.M.F. is generated since there is No Relative
Motion.
However, if the Electric Current is made to vary in
Magnitude and/or Polarity, then there would be an Induction
of an E.M.F into the second Conductor, i.e., this
variation/change in Magnetic Flux has the same Effect as
Relative Motion between the Magnetic source and the
Conductor
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