What is the name of the electrical device that changes voltage?

The device that changes voltage is called a transformer. Transformers operate on the principle of electromagnetic induction and are essential in electrical systems for either stepping up (increasing) or stepping down (decreasing) voltage levels. They consist of two coils of wire, known as the primary and secondary coils, wound around a core, usually made of iron. When alternating current (AC) flows through the primary coil, it creates a magnetic field that induces a current in the secondary coil. The ratio of the number of turns of wire in the primary and secondary coils determines the change in voltage.

In contrast, a resistor is primarily used to limit current flow in a circuit and does not change voltage. A capacitor stores electrical energy temporarily and affects voltage and current in AC circuits but does not change voltage levels directly like a transformer does. A conductor simply refers to a material that allows electric current to flow through it and does not perform any voltage transformation. Therefore, the function of altering voltage is uniquely attributed to transformers.