Both single-phase and polyphase AC motors are produced by LEESON and many other manufacturers. In polyphase motors, the placement of the phase winding groups in conjunction with the phase sequence of the power supply line produces a rotating field around the rotor surface.
The rotor tends to follow this rotating field with a rotational speed that varies inversely with the number of poles wound into the stator. Singlephase motors do not produce a rotating field at a standstill, so a starter winding is added to give the effect of a polyphase rotating field. Once the motor is running, the start winding can be cut out of the circuit, and the motor will continue to run on a rotating field that now exists due to the motion of the rotor interacting with the single-phase stator magnetic field.
If arranged in a circle, the lights would appear to rotate. The speed of this ”rotation” depends on the frequency of the on/off blinking.
Follow-up question: what electrical change(s) would you have to make to reverse the direction of the lights’ apparent motion?
Challenge question: what would happen to the apparent motion of the lights if one of the phases (either 1, 2, or 3) were to fail, so that none of the bulbs with that number would ever light up?
The compass needle would rotate. Challenge question: what would happen to the apparent motion of the magnetic field if one of the phases
(either 1, 2, or 3) were to fail, so that none of the coils with that number would ever energize?
The magnetic rotor will rotate as it tries to orient itself with the rotating magnetic field.
Follow-up question: what must we do with the AC power energizing the coils to increase the rotor’s rotational speed?