magnetomotive force

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.

The standard definition of magnetomotive force involves current passing through an electrical conductor, which accounts for the magnetic fields of electromagnets as well as planets and stars. Permanent magnets also exhibit magnetomotive force, but for different reasons.

Units

The 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 [1], is the CGS unit of magnetomotive force. 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.

Equations

The magnetomotive force in an inductor is given by:

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

Reference

• The Penguin Dictionary of Physics, 1977, ISBN 0-14-051071-0

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