Which of the following is a requirement for a transformer to function effectively?

A transformer requires proper efficiency to function effectively because its primary role is to transfer electrical energy between its windings with minimal losses. Efficiency in a transformer is determined by how well it converts input energy to output energy without significant losses due to factors such as heat from copper losses (resistance in the windings) and core losses (hysteresis and eddy currents in the magnetic core).

When a transformer operates at high efficiency, it means that most of the electrical energy is being transformed from one voltage level to another while retaining its integrity, which is essential for the reliability of electrical systems. While voltage levels, resistance, and current can influence how well a transformer performs, these factors are not requirements for effective operation in the same way that efficiency is.