What primarily enables energy transfer in a transformer?

• A. Direct electrical connection between windings.
• B. Capacitive coupling between windings.
• C. Conduction through the iron core.
• D. Electromagnetic coupling via changing magnetic flux in the core.

Answer: (D)

The energy transfer in a transformer is driven by electromagnetic coupling through a changing magnetic flux in the core. When the primary winding carries alternating current, it creates a time-varying magnetic field that travels through the high-permeability iron core. This changing flux links with the secondary winding and induces a voltage there, with the magnitude determined by the turns ratio and Faraday’s law. The core’s job is to provide a low-reluctance path for the flux, maximizing coupling and minimizing leakage, so most of the magnetic energy is transferred from primary to secondary rather than being lost in the surrounding space.

Direct electrical connection between windings would defeat isolation and isn’t how power is transferred. Capacitive coupling between windings is negligible at power frequencies and cannot account for the main energy transfer. The core might conduct magnetic flux well, but energy moves via the evolving magnetic field, not through conduction in the core.