Magnetomotive force


Magnetomotive force
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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 [1]. 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.

References


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  • 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

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  • 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