For you technically minded individuals, here is a short explanation of the working of the alternator:

 The rotor is an iron core, or armature, with a field of copper wire (called a winding) wrapped around it.  A 12-volt current supplied to the rotor produces a magnetic field around the iron center, which results in changing the rotor to an electromagnet.  The rotor is mounted to the alternator housing via front and back bearings.

Three fields of copper windings are fixed to the alternator housing, called a stator.  As the engine is turning the rotor, the windings on the stator are subjected to a rapid change of magnetic field (remember the rotor is an electromagnet), which in turn produces alternating current (AC) electricity (as in your home). The diodes, or rectifier, set in the back (“3 dime-sized electronic buttons”), convert this AC current to direct current (DC – the kind your car uses).  The Voltage Regulator (VR) controls the output of the alternator, using the battery input voltage.  If the battery voltage drops, the VR will allow more voltage to the rotor, which will increase the magnetic field and this will increase the electric current generated.