Basic Electrical Theory
MAGNETISM
Figure 24 Left-hand Rule to Find North Pole of an Electromagnet
Magnetomotive Force
Magnetomotive force (mmf) is the strength of a magnetic field in a coil of wire. This is
dependent on how much current flows in the turns of coil: the more current, the stronger the
magnetic field; the more turns of wire, the more concentrated the lines of force. The current
times the number of turns of the coil is expressed in units called "ampere-turns" (At), also known
as mmf. Equation (1-13) is the mathematical representation for ampere-turns (At).
Fm = ampere-turns = NI
(1-13)
where
Fm
=
magnetomotive force (mmf)
N
=
number of turns
I
=
current
Rev. 0
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