Which device is used to reduce voltage in electrical circuits?

The step-down transformer is specifically designed to reduce voltage in electrical circuits. It operates on the principle of electromagnetic induction, where the primary coil receives alternating current (AC) voltage, and this induces a lower voltage in the secondary coil. The ratio of the number of turns in the primary coil to the number of turns in the secondary coil determines the voltage reduction; thus, when the secondary coil has fewer turns, the voltage decreases proportionally.

In contrast, a step-up transformer serves to increase voltage by having more turns in the secondary coil compared to the primary. A generator converts mechanical energy into electrical energy but does not inherently modify voltage levels. A rectifier is used to convert alternating current (AC) to direct current (DC) but does not change the voltage level itself. Therefore, for reducing voltage, the step-down transformer is the correct device.