In what type of applications are transformers most commonly used?

Transformers are primarily utilized in AC power transmission and distribution systems due to their ability to efficiently step-up or step-down voltage levels. This functionality is critical in transmitting electricity over long distances, as higher voltages reduce energy losses in the conductors. When electricity is transmitted at high voltages, the current decreases, which minimizes resistive losses according to Joule's law. Upon reaching the vicinity of consumption, transformers can reduce the voltage to safe and usable levels for residential or industrial applications.

In contrast, direct current (DC) circuits do not work with transformers since they rely on changing current to induce voltage in the secondary coil. Some industrial settings and electronic devices may utilize transformers, but their primary and most critical role is in the AC transmission and distribution networks, where they facilitate efficient energy transfer from power plants to end-users.