Transformers operate based on which principle involving coils?

• A. Capacitive coupling
• B. Magnetic induction
• C. Electric conduction
• D. Thermal conduction

Answer: (B)

Transformers operate on magnetic induction: when the current in the primary coil changes, it creates a changing magnetic flux in the core, and that changing flux induces a voltage in the secondary coil according to Faraday's law. The alternating current makes the flux vary continuously, and the turns ratio between windings sets the relationship between primary and secondary voltages. The iron core concentrates the magnetic flux to improve coupling and efficiency. Capacitive coupling would involve an electric field path, which is not how power is transferred between windings; electric conduction would require a direct electrical path, which isn’t present between isolated windings; and thermal conduction is about heat transfer, not transferring electrical energy.