Magnetomotive Force:

MMF (Magnetomotive force) is the strength of a magnetic field in a coil of wire. This is dependent on how many current flows in the turns of coil:  the more current makes stronger the magnetic field; the more turns of wire, a more concentrated the lines of force.   A current time the number of turns of the coil is expressed in units called "ampere-turns" (At), also known as mmf. The given Equation (1-13) is the mathematical representation for ampere-turns (At).

F_m = ampere-turns = NI                              (1-13)

where

F_m= magnetomotive force (mmf)

N= number of turns

I= current

Example: To Calculate the ampere-turns for a coil with 1000 turns and a 5 mA current.

N = 1000 turns and I = 5 mA

substitute

N = 1000 turns and I = 5 x 10^-3

NI = 1000 (5 x 10^-3) = 5 At