Final answer:
A single phase motor’s run winding alone isn't generally enough to start the rotor due to lack of starting torque. Additional components like a start winding with a capacitor are needed to create a phase shift and produce a rotating magnetic field. Once running, the motor adjusts current flow to match load conditions for efficient operation.
Step-by-step explanation:
In a single phase motor, the run winding does produce a pulsating magnetic field. However, this by itself generally isn't enough to start the rotor turning due to lack of starting torque. That's why single phase motors often need additional components, such as a start winding with a capacitor, to create a phase shift and produce a rotating magnetic field which can start the rotor. Once the motor is running, if a mechanical load is applied, the motor may slow down causing the back emf to drop, which in turn allows more current to flow, enabling the motor to do more work. But if the motor slows too much, the increased current can cause overheating and potentially damage the motor. At optimal conditions, with no mechanical load beyond friction, the motor reaches a speed where the back emf nearly equals the input emf for efficient operation.