Magnetomotive force

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Magnetomotive force is any physical cause that produces magnetic flux. It is analogous to electromotive force or voltage in electricity.

In this context, the word "force" is used in a general sense of "that which has a physical effect", and is not the same as mechanical force measured in newtons.

Although the standard definition of magnetomotive force involves current passing through an electrical conductor, permanent magnets also exhibit magnetomotive force. The same is true for planets with magnetic fields, such as the Earth, Jupiter, Saturn, Uranus, and Neptune. The Sun also generates magnetomotive forces, particularly near sunspots.

Units

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 gilbert (Gi), established by the IEC in 1930 [link], is the CGS unit of magnetomotive force. The gilbert is defined differently, and is a slightly smaller unit than the ampere-turn.

[\begin1\ Gi & = & } \ \mbox \\ & \approx & 0.795773 \ \mbox\end]

Equations

The magnetomotive force [\mathfrak F] in an inductor is given by:

[\mathfrak F = N I = \Phi R]

where N is the number of turns of the coil, I is the current in the coil, Φ is the magnetic flux and R is the reluctance of the magnetic circuit.

Reference

The Penguin Dictionary of Physics, 1977, ISBN 0140510710

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