Magnetomotive force

Magnetic circuits
Part of a series on
Conventional magnetic circuits
Magnetomotive force ${\mathcal {F}}$ Magnetic flux $\Phi$ Magnetic reluctance $\mathcal R$
Phasor magnetic circuits
Complex reluctance $Z_\mu$
Related concepts
Magnetic permeability $\mu$
Gyrator-capacitor model variables
Magnetic impedance $z_\mathrm{M}$ Effective resistance $r_\mathrm{M}$ Magnetic inductivity $L_\mathrm{M}$ Magnetic capacitivity $C_\mathrm{M}$
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In physics, the magnetomotive force is a quantity appearing in the equation for the magnetic flux in a magnetic circuit, sometimes known as 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 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]

ℱ = NI
where N is the number of turns in the coil and I is the electric current through the circuit. Sometimes the unit of gilbert is used to express ℱ.
ℱ = ΦR
where Φ is the magnetic flux and R is the reluctance
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

Notes

↑ Smith, R.J. (1966), Circuits, Devices and Systems, pp 495-506, Wiley International Edition, New York.

References

The Penguin Dictionary of Physics, 1977, ISBN 0-14-051071-0
A textbook of Electrical Technology, 2008, ISBN 81-219-2440-5
Smith, R.J. (1966), Circuits, Devices and Systems, Chapter 15, Wiley International Edition, New York. Library of Congress Catalog Card No. 66-17612

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