An induction motor is simply an electric transformer whose
magnetic circuit is separated by an air gap into two relatively
movable portions, one carrying the primary and the other the
secondary winding. Alternating current supplied to the primary
winding from an electric power system induces an opposing
current in the secondary winding, when the latter is shortcircuited
or closed through external impedance. Relative
motion between the primary and secondary structure is
produced by the electromagnetic forces corresponding to the
power thus transferred across the air gap by induction.