Which of the following is used to control voltage levels within a circuit?

A transformer is an electrical device specifically designed to control voltage levels within a circuit by varying the voltage according to the turns ratio between its primary and secondary windings. When alternating current (AC) passes through the primary coil, it generates a magnetic field that induces a voltage in the secondary coil. By adjusting the number of turns in the primary and secondary coils, transformers can increase or decrease voltage levels efficiently, making them essential in power distribution systems and various electronic applications.

While resistors, capacitors, and inductors play vital roles in controlling current flow, storing energy, and filtering signals, they do not primarily function to alter voltage levels in the way transformers do. Resistors are used to limit current by providing resistance, capacitors store electrical energy and can smooth voltage levels, and inductors store energy in a magnetic field and can influence current flow over time. None of these components are designed to step up or step down voltage levels as transformers are.