Principle of the solid-rotor induction motor
Alternating current meters - Electromechanical meters

To produce torque on a freely rotating armature, it must be subjected to two alternating fluxes:

• which are not in phase with each other in time;

• which are applied to the armature at two different points, aligned according to the direction of the desired movement.

This principle is illustrated in figure 1 where we see symbolically represented two elementary induction fluxes b₁ and b₂ creating elementary currents i₁ and i₂ and therefore elementary forces f₁ and f₂ . Rotation only occurs if b₁ and b₂ are out of phase.