What is the name of the electromagnetic device that changes voltage from one level to another?

The device that changes voltage from one level to another is called a transformer. A transformer operates on the principle of electromagnetic induction, which allows it to increase (step-up) or decrease (step-down) the voltage of an alternating current (AC) signal while maintaining the same frequency. This is achieved through the use of two coils of wire, known as the primary and secondary windings, wrapped around a magnetic core. When an AC voltage is applied to the primary winding, it creates a magnetic field that induces a voltage in the secondary winding according to the turns ratio of the coils. This capability is essential in electrical power distribution systems, where high voltages are used for efficient long-distance transmission, and lower voltages are needed for end-use applications.

In contrast, an inductor stores energy in a magnetic field when current flows through it, while a capacitor stores energy in an electric field. A relay is an electromagnetic switch used to control the power to a circuit, but it does not change voltage levels.