Magneto-motive Force

In physics, the magnetomotive force (mmf) ${\displaystyle {\mathcal {F}}}$ 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:

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

${\displaystyle {\mathcal {R}}}$

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. ${\displaystyle {\mathcal {F}}=\Phi {\mathcal {R}}}$
   where Φ is the magnetic flux and ${\displaystyle {\mathcal {R}}}$ 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.