What principle does a transformer operate on?

A transformer operates on the principle of electromagnetic induction. This fundamental concept involves the generation of an electromotive force (EMF) in a circuit due to a changing magnetic field. In a transformer, alternating current flows through the primary coil, creating a time-varying magnetic field around it. This magnetic field induces a voltage in the secondary coil, allowing for the transfer of electrical energy between the two coils.

The efficiency of a transformer relies heavily on this principle, as it enables the conversion of high voltage to low voltage, or vice versa, without moving parts. This mechanism is crucial in various applications, such as power distribution and electrical isolation.

The other choices do not pertain to how transformers function: thermal conduction relates to heat transfer, electric resonance concerns the oscillation of electrical networks, and capacitance variation involves changes in the capacity of a capacitor to store electrical energy. These principles do not apply to the operation of transformers, emphasizing why electromagnetic induction is the correct answer.