# Magnetomotive force

Magnetomotive force
Magnetic Circuits

Conventional Magnetic Circuits
• Magnetomotive force $\mathcal F$
• Magnetic flux Φ
• Magnetic reluctance $\mathcal R$

Phasor Magnetic Circuits

Related Concepts

Gyrator-capacitor model variables
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Magnetomotive force (MMF) (SI Unit: Ampere) is any physical driving (motive) force that produces magnetic flux. In this context, the expression "driving force" is used in a general sense of "work potential", and is analogous, but distinct from 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.

## SI versus CGS units

The SI unit of magnetomotive force is the ampere (A), 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 . The gilbert is defined differently, and is a slightly smaller unit than the ampere. The unit is named after William Gilbert (1544–1603) English physician, astronomer and natural philosopher.

The conversion factor between the SI and CGS units is $\frac {10}{4\pi}$ (≈ 0.795774715) ampere for every gilbert.

Between the CGS unit and SI unit, the MKS unit magnetomotive force was the ampere-turn At.

## Equations

The magnetomotive force $\mathcal{F}$ in an inductor or electromagnet consisting of a coil of wire is given by: $\mathcal{F} = N I$

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: $\mathcal{F} = \Phi \mathcal{R}$

where Φ is the magnetic flux and $\mathcal{R}$ 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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### Look at other dictionaries:

• magnetomotive force — n. The force that produces magnetic flux. [WordNet 1.5] …   The Collaborative International Dictionary of English

• magnetomotive force — magnetovara statusas T sritis automatika atitikmenys: angl. magnetomotive force vok. Durchflutung, f; magnetomotorische Kraft, f rus. магнитодвижущая сила, f pranc. force magnétomotrice, f …   Automatikos terminų žodynas

• magnetomotive force — magnetovara statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas atitikmenys: angl. magnetomotive force vok. magnetomotrische Kraft, f rus. магнитодвижущая сила, f pranc. force… …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• magnetomotive force — magnetovara statusas T sritis fizika atitikmenys: angl. magnetomotive force vok. magnetomotorische Kraft, f rus. магнитодвижущая сила, f pranc. force magnétomotrice, f …   Fizikos terminų žodynas

• magnetomotive force — noun the force that produces magnetic flux • Hypernyms: ↑force …   Useful english dictionary

• magnetomotive force — noun Date: 1883 a force that is the cause of a flux of magnetic induction …   New Collegiate Dictionary

• magnetomotive force — noun the force associated with a magnetic field and that produces magnetic flux; it is the work required to carry a magnetic monopole of unit strength once round a magnetic circuit; measured in ampere turns …   Wiktionary

• magnetomotive force — mag•ne′to•mo′tive force′ [[t]mægˈni təˈmoʊ tɪv, ˌni [/t]] n. elm a scalar quantity that is a measure of the sources of magnetic flux in a magnetic circuit • Etymology: 1883 …   From formal English to slang

• magnetomotive force — /mægˌnitoʊˌmoʊtɪv ˈfɔs/ (say mag.neetoh.mohtiv faws) noun the force which gives rise to magnetic effects or magnetic induction, calculated as the magnetic flux multiplied by reluctance …   Australian-English dictionary

• magnetomotive force — /mag nee teuh moh tiv, nee /, Elect. a scalar quantity that is a measure of the sources of magnetic flux in a magnetic circuit. Abbr.: mmf [1883; MAGNETO + MOTIVE] * * * …   Universalium