What type of device converts an automobile's mechanical energy into electrical energy?

An alternator is a device in automobiles that converts mechanical energy into electrical energy. It operates by using the principles of electromagnetic induction, where a rotating magnetic field generates alternating current (AC) electrical energy. As the engine runs, it powers the alternator, which in turn converts the rotational energy into electricity, providing power to the electrical systems of the vehicle and recharging the battery.

The alternator is specifically designed for this purpose in vehicles, making it a crucial component for the electrical system's efficiency and performance. It allows for a steady supply of electricity, which is essential for operating lights, the ignition system, and other electronic components while the engine is in operation. Thus, identifying the alternator as the answer reflects an understanding of its primary function in converting mechanical energy into usable electrical energy in an automobile.