Which device is specifically designed to convert mechanical energy into electrical energy using alternating current?

The alternator is specifically designed to convert mechanical energy into electrical energy using alternating current. This device operates on the principle of electromagnetic induction, where a coil of wire rotates within a magnetic field, or a magnetic field moves past a coil of wire. As this occurs, it induces an alternating voltage and current in the coil, effectively generating electrical energy.

Unlike a standard generator, which can produce direct current (DC) or alternating current (AC), an alternator is optimized for the production of alternating current. This makes it particularly useful in automotive applications and power generation where AC power is required.

In contrast, while a generator can refer to devices that produce both DC and AC, it doesn't exclusively indicate AC generation like an alternator does. A motor, on the other hand, converts electrical energy into mechanical energy, and a transformer is used to change the voltage of an alternating current without converting mechanical energy into electrical energy. Therefore, the alternator stands out as the correct choice for directly converting mechanical energy into electrical energy in the form of alternating current.