Which device converts mechanical energy into electrical energy?

The generator is the device that converts mechanical energy into electrical energy. This process relies on electromagnetic induction, where a coil of wire is rotated within a magnetic field, producing an electric current. Generators are commonly used in various applications, including power plants, where they convert kinetic energy from steam turbines or water flow into electrical energy that can be distributed for public use.

In contrast, a motor converts electrical energy into mechanical energy, making it work in the opposite direction compared to a generator. A transformer is designed to change the voltage of an alternating current (AC) electrical signal and does not convert energy types. A battery stores chemical energy and releases it as electrical energy, but it does not directly involve the conversion of mechanical energy. Overall, the generator's fundamental role in energy conversion is what distinguishes it as the correct answer in this context.