1. AC Generators use slip rings NOT slip ring commutators and as such, do not change the direction of the current. This allows current to alternate in each direction periodically to create AC.
2. AC Motors use split rings where the magnetic field is produced by electromagnets connected in series with the current through the rotor coils - this allows the magnetic field to switch in direction as the current changes in direction. It effectively allows the motor to run like a DC motor.
3. DC Generators use split ring commutators to change the direction of the current in the rotor coil.
4. DC Motors use split ring commutators, also to change the direction of the current in the rotor.
A slip ring consists of two rings connected to either end of the rotor coil and at either end of the power source.
Diagram:
http://everythingscience.co.za/grad...pictures/a9a84dfde6226fde8500d1abd73e621d.png
A split ring consists of a single ring split into at least 1 pair of segments. As the coil rotates, the commutator effectively switches the terminal of the power source of which the rotor coil is connected to.
Diagram:
http://everythingscience.co.za/grad...pictures/0ffe6a062725fefa6d31b021c15c878f.png