Which device is used to alter the voltage level of AC?

A transformer is specifically designed to alter the voltage level of alternating current (AC). It operates based on the principle of electromagnetic induction, allowing it to either step up (increase) or step down (decrease) the voltage level while maintaining the frequency of the current. This device consists of two coils, the primary and secondary windings, wrapped around a common core. When AC flows through the primary coil, it generates a magnetic field that induces voltage in the secondary coil, thus changing the voltage level according to the turns ratio between the two coils.

In comparison, a circuit breaker is a safety device used to protect electrical circuits from overload or short circuits but does not change voltage levels. A rectifier transforms AC into direct current (DC) and is not involved in voltage level alteration. An inverter performs the opposite of a rectifier by converting DC back into AC, which does not involve changing the voltage levels of an existing AC supply. Therefore, the transformer is the appropriate device for altering the voltage level of AC.