The field inside a solenoid is strong and uniform ... The magnetic field produced by the current in a coil of wire: is very similar to the field of a bar magnet; reverses when the direction ...

Anyone who has ever wound a toroidal coil by hand can tell you that it ... which generally have relatively few windings, passing all that wire through the toroid time after time is a pain.

As the rotation continues and that side of the coil moves down, the induced potential difference reverses direction. This means that the alternator produces a current that is constantly changing.