When using a transformer, what is transferred from the primary to the secondary?

In a transformer, the key principle is that it transfers power from the primary winding to the secondary winding through electromagnetic induction. This transfer occurs while maintaining the relationship of voltage and current based on the turns ratio of the transformer.

When voltage is increased in the primary winding, the current decreases in the secondary, and vice versa, ensuring that the total power remains constant (neglecting losses). This means that while individual voltages and currents change based on the turns ratio, the overall power being transferred—calculated as the product of voltage and current—remains consistent across the transformer's primary and secondary windings.

Resistance is not transferred, as it is a characteristic of the materials used in the windings rather than a parameter that changes hands during operation. Therefore, understanding that the fundamental function of a transformer is to transfer power helps clarify the operation and design of electrical systems where transformers are employed.