What is the primary function of a transformer?

The primary function of a transformer is to step up or step down voltage levels. Transformers operate on the principle of electromagnetic induction and are designed to change the voltage of alternating current (AC) while maintaining the same power level, assuming negligible losses.

When a transformer increases voltage, it is referred to as a step-up transformer, which is useful for transmitting electricity over long distances, as higher voltages result in lower current, minimizing energy loss due to resistance in the transmission lines. Conversely, a step-down transformer reduces voltage, making it suitable for household applications where lower voltages are safer and more practical for use with appliances.

The other options present functions that are not associated with transformers. Converting AC to DC is a task performed by rectifiers, measuring electrical current involves devices such as ammeters, and circuit protection is typically handled by breakers and fuses. Thus, the correct answer aligns perfectly with the fundamental purpose of transformers in electrical systems.