One other little scientific tidbit:
Electrons do not travel through wire, they actually travel along the surface of the conductor(s).
AC current experiences the Skin Effect
DC travels through the bulk of the conductor, unless you are dealing with high-frequency DC.
Cool, I didn't know that.
Where does regulated DC of the average vehicle fall into the frequency range?
As for the starter, coming off the battery, there is not any frequency, it's flat.
As for what the alternator produces, that varies with the RPM
. (Every hear a bad alternator through an old radio? The sound goes up and down with the motor.)
As for what comes out of the alternator, that depends on filtering. Capacitors flatten out the waves, and the battery also has an impact.