A __________ is an electrical device that converts AC electricity from one voltage level to another.

A transformer is an electrical device specifically designed to change the voltage level of alternating current (AC) electricity while maintaining the same frequency. It operates based on the principle of electromagnetic induction. A transformer consists of two coils of wire, known as the primary coil and the secondary coil, which are wound around a magnetic core.

When AC electricity flows through the primary coil, it creates a varying magnetic field. This magnetic field induces a voltage in the secondary coil, enabling the transformer to either step up (increase) or step down (decrease) the voltage to the desired level. The ratio of turns between the primary and secondary coils determines the output voltage, making transformers essential components in electrical power distribution systems, where they efficiently manage voltage levels for transmission and distribution.

The other terms listed relate to different components or configurations within the context of transformers but do not define the device itself that changes voltage levels. The secondary coil and primary coil are parts of a transformer, while a center tap is a specific configuration of a secondary coil used for specific voltage requirements, but none of these options serves as the definition of the device that fulfills the role of converting AC electricity to different voltage levels.