The basis for transformer operation in AC is mutual inductance.

• A. Capacitance.
• B. Reactance.
• C. Inductance.
• D. Impedance.

Answer: (C)

Transformers rely on the ability of coils to couple through a changing magnetic field, which comes from inductance and mutual inductance. When AC flows in the primary, it creates a time-varying magnetic flux in the core that links the secondary winding. The changing flux induces an emf in the secondary proportional to the rate of change of the primary current, a direct consequence of inductive coupling between the windings. Capacitance would involve electric fields and isn’t what transfers energy between the windings in normal transformer operation. Impedance and reactance describe how circuits oppose AC, but the fundamental mechanism that makes a transformer work is inductance through mutual induction between the windings.