What device is used to change AC to DC?

The correct device used to change alternating current (AC) to direct current (DC) is the commutator. A commutator is a mechanical switch in rotary machinery that reverses the current direction in the coil windings of motors or generators. This action converts the alternating current generated in the windings into direct current, allowing the electrical output to remain constant in one direction.

Transformers are primarily used to increase or decrease the voltage of AC electricity but do not convert AC to DC. Capacitors store electric charge and can smooth out fluctuations in DC voltage, while resistors limit current flow and dissipate energy as heat. Both capacitors and resistors perform essential functions in electrical circuits but do not have the role of converting AC to DC.