Electromagnetic field force is often quantified or measured as magnetomotive force (mmf).
Magnetomotive force (mmf) is determined by two factors:
• The amount of current flowed through the conductor
• The number of turns of wire in a coil
Magnetomotive force is measured in ampere-turns (At). Ampere-turn factors are the number of windings (complete turns of a wire conductor) and the quantity of current flowed (measured in amperes). For instance, if a coil with 100 windings has 1 ampere of current flowed through it, the result will be a magnetic field strength rated at 100 At. An identical magnetic field strength rating could be produced by a coil with 10 windings with a current flow by 10 amperes. The actual field strength must factor in reluctance. In other words, the actual field strength of both coils would be increased if the coil windings were to be wrapped around an iron core. A pair of coils of equal field strength, but because of its larger number of windings, the one on the left requires much less current flow.
A common use of an electromagnet would be that used in an automobile salvage yard crane. By switching the current to the lift magnet on and off, the operator can lift and release scrap cars. Electromagnetic principles are used extensively in vehicle electrical systems. They are the basis of every solenoid, relay, coil, generator, and electric motor.