Dictionary:
mag·ne·to·mo·tive force (măg-nē'tō-mō'tĭv) ![]() |
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The magnetomotive force (mmf) around a magnetic circuit is the work per unit magnetic pole required to carry the pole once around the circuit. It is the analog of electromotive force.
It is expressed mathematically in the equation below,
where H cos θ is the component of magnetic field strength in the direction of a length of path ds. The line integral is taken around any closed path in the field.
| Veterinary Dictionary: MMF |
Maximal midexpiratory flow (rate).
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| Magnetic Circuits |
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Conventional Magnetic Circuits |
Magnetomotive force ![]() |
| Magnetic flux Φ |
Magnetic reluctance ![]() |
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Phasor Magnetic Circuits |
| Complex reluctance Zμ |
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Related Concepts |
| Magnetic permeability μ |
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Gyrator-Capacitor Model variables |
| Magnetic impedance zM |
| Effective resistance rM |
| Magnetic inductivity LM |
| Magnetic capacitivity CM |
Magnetomotive force (MMF) (SI Unit: At) is any physical force that produces magnetic flux. In this context, the word "force" is used in a general sense of "work potential", and is analogous to, but distinct from mechanical force measured in newtons. The name came about because in magnetic circuits it plays a role analogous to the role electromotive force (voltage) plays in electric circuits.
The SI unit of magnetomotive force is the ampere-turn (At), represented by a steady, direct electric current of one ampere flowing in a single-turn loop of electrically conducting material in a vacuum.
The CGS unit of magnetomotive force is the gilbert (Gi), established by the IEC in 1930 [1]. The gilbert is defined differently, and is a slightly smaller unit than the ampere-turn. The unit is named after William Gilbert (1544–1603) English physician and natural philosopher.
The conversion factor between the SI and CGS units is
(≈ 0.795774715) Ampere-turns for every gilbert.
The magnetomotive force
in an inductor or electromagnet consisting of a coil of wire is given by:

where N is the number of turns of wire in the coil and I is the current in the wire.
The equation for the magnetic flux in a magnetic circuit, sometimes known as Hopkinson's law, is:

where Φ is the magnetic flux and
is the reluctance of the magnetic 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.
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| mmf (abbreviation) | |
| ampere·turn (magnetomotive force) | |
| gilbert (electromagnetism) |
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