Which device would be used to control the amount of voltage in a circuit?

A transformer is the device specifically designed to control the amount of voltage in a circuit. It operates on the principle of electromagnetic induction and is used to increase or decrease voltage levels as needed. By adjusting the ratio of turns of wire in its primary and secondary coils, a transformer can step up (increase) or step down (decrease) the voltage while maintaining the overall power level, with some losses due to efficiency.

In practical applications, this is essential for power distribution systems where the voltage needs to be altered for safe use or transmission over long distances. For instance, electricity is typically transmitted at high voltages to minimize losses over distances, and transformers are used to reduce this voltage to safer levels for residential or commercial use.

The capabilities of capacitors, resistors, and diodes are quite different; capacitors store and release electrical energy, resistors limit current flow and dissipate energy as heat, while diodes allow current to flow in one direction only, providing rectification but not voltage control. These functions are not aimed at voltage control in the way transformers are designed to adjust voltage levels directly.