Reed Relays and
Electronics India Limited

# Magneto-motive Force

Magneto-motive force is a quantity representing the line integral of the magnetic intensity around a closed line and is expressed in Ampere-Turns.

In physics, the magnetomotive force (mmf) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, often called Ohm's law for magnetic circuits. It is the property of certain substances or phenomena that give rise to magnetic fields:

${\displaystyle {\mathcal {F}}=\Phi {\mathcal {R}},}$

where Φ is the magnetic flux and R is the reluctance of the circuit. It can be seen that the magnetomotive force plays a role in this equation analogous to the voltage V in Ohm's law: V = IR, since it is the cause of magnetic flux in a magnetic circuit:

1. ${\displaystyle {\mathcal {F}}=NI}$
where N is the number of turns in the coil and I is the electric current through the circuit.
2. ${\displaystyle {\mathcal {F}}=\Phi R}$
where Φ is the magnetic flux and R is the magnetic reluctance
3. ${\displaystyle {\mathcal {F}}=HL}$
where H is the magnetizing force (the strength of the magnetizing field) and L is the mean length of a solenoid or the circumference of a toroid.
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