 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 (abbreviated mmf or MMF, symbol ${\mathcal {F}}$ ) is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, Hopkinson's law. It is the property of certain substances or phenomena that give rise to magnetic fields:

${\mathcal {F}}=\Phi {\mathcal {R}},$ where Φ is the magnetic flux and ${\mathcal {R}}$ 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. ${\mathcal {F}}=NI$ where N is the number of turns in the coil and I is the electric current through the circuit.
2. ${\mathcal {F}}=\Phi {\mathcal {R}}$ where Φ is the magnetic flux and ${\mathcal {R}}$ is the magnetic reluctance
3. ${\mathcal {F}}=HL$ 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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