Also, the rotating magnet is not a permenent magnet, but an electro magnet, thus the current which creates the magnetic field can be controlled and is applied via slip ring, just like your alternator in you car. Some have a permenent magnet just to get things started. If no load is applied there will be no current, but as you apply load, you draw energy and the removal of energy comes from the mover or stored energy of rotating, thus draw energy, rotor slows down or engine works harder.
Mike, I disagree that current is induced in the stator, it is voltage and current is determined by the load.