AC induction motor: Armature in a whirling field.

AC induction motor: Armature in a whirling field. This is an old AC induction motor with casing removed. Throwing the switch causes a rotating field in the ring of coils. The rotating field induces eddy currents in the squirrel cage armature. The armature eddy currents produce magnetic fields in a direction opposite to the rotating coil field. This causes the armature to rotate without any electrical connection between the coils and the armature. The speed of rotation can be varied by sliding the core in or out of the coil, or by varying the rheostat. The armature can be removed, and a piece of translucent plastic laid on the top of the ring of coils. Iron filings sprinkled on the plastic whirl in a circle when the A.C. is turned on.