What device is used to alter the voltage level of an alternating current?

A transformer is the device that alters the voltage level of an alternating current (AC). It operates on the principle of electromagnetic induction, which allows it to step up (increase) or step down (decrease) the voltage of AC power. When alternating current flows through the primary coil of a transformer, it generates a changing magnetic field, which then induces a voltage in the secondary coil. The ratio of the number of turns in the primary and secondary coils determines whether the voltage is increased or decreased.

Transformers are essential in power transmission systems, allowing electricity to be transmitted over long distances at high voltages, which reduces energy loss due to resistance in the wires. The ability to efficiently convert voltage levels makes transformers indispensable in electrical engineering and energy distribution.

The other devices mentioned have different functions. An inductor stores energy in a magnetic field when an electric current passes through it. A capacitor stores energy in an electric field and is primarily used for smoothing out voltage fluctuation or filtering signals. A battery provides a constant direct current (DC) voltage rather than altering AC voltage levels.