Basic Electrical Theory MAGNETISMFigure 24 Left-hand Rule to Find North Pole of an ElectromagnetMagnetomotiveForceMagnetomotive force (mmf) is the strength of a magnetic field in a coil of wire. This isdependent on how much current flows in the turns of coil: the more current, the stronger themagnetic field; the more turns of wire, the more concentrated the lines of force. The currenttimes the number of turns of the coil is expressed in units called "ampere-turns" (At), also knownas mmf. Equation (1-13) is the mathematical representation for ampere-turns (At).F_{m} = ampere-turns = NI (1-13)whereF_{m}= magnetomotive force (mmf)N = number of turnsI = currentRev. 0 Page 33 ES-01

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