How does a transformer function in an electrical circuit?

A transformer functions primarily by changing the voltage levels in an electrical circuit. It operates on the principle of electromagnetic induction, consisting of two windings - the primary and the secondary - wrapped around a magnetic core. When alternating current flows through the primary winding, it creates a magnetic field. This magnetic field induces a voltage in the secondary winding, which can either increase or decrease the voltage level depending on the turns ratio between the two windings. This capability is crucial for efficiently transmitting electricity over long distances and for adapting voltage levels to meet the needs of different devices or circuits.

The other options describe functions that are not applicable to transformers. For instance, transformers do not store energy; their role is to transfer electrical energy between circuits. They also do not measure electrical resistance, as that is the function of an ohmmeter or similar devices. Finally, while transformers are vital in electrical systems, they do not directly control circuit breakers, which operate as protective devices in response to overloads or faults.