What component changes 120 V AC power to a lower AC voltage for other uses?

A transformer is an electrical component consisting of two or more coils of wire wrapped around a common core. By varying the ratio of turns in each coil, a transformer can step down (or step up) alternating current (AC) voltages, such as converting 120 V AC from a wall outlet to a lower AC voltage for use in electronic devices. The other options serve completely different purposes. A diode allows current to flow in only one direction and is often used to convert AC to DC, but it does not change AC voltage levels. Transistors are used for amplifying or switching signals, and variable capacitors are used to tune frequencies in radio circuits.