How does a transformer work?

• A. The energy transfer occurs through direct conduction between windings without magnetic field involvement.
• B. The energy transfer requires a direct electrical connection between primary and secondary windings.
• C. An alternating current in the primary produces a changing magnetic flux in the core, which induces a voltage in the secondary.
• D. The transformer converts DC into AC.

Answer: (C)

A transformer works by transferring energy through a changing magnetic field in a shared core. When the primary winding is fed with an alternating current, it creates a time-varying magnetic flux in the core. This changing flux links the secondary winding, and Faraday’s law tells us that a changing flux induces a voltage in the coil. The induced voltage in the secondary is proportional to the turns ratio between the windings, and the power delivered to the load comes from the primary, with the currents adjusting so power is approximately conserved. Because the energy moves through the magnetic field rather than a direct electrical connection, there’s no physical link between the two windings.

Why the other ideas don’t fit: energy isn’t transferred by direct conduction between windings, so a direct electrical connection would defeat the purpose and typically short the source. Using direct current in the primary would establish a steady magnetic field with no changing flux, so no continuous voltage is induced in the secondary. The device can transform voltage and current for AC signals, not DC.