_____ is an electrical device that changes one value of AC voltage into another value of AC voltage.

• A. Condenser
• B. Transformer
• C. Rotor
• D. Inductor

Answer: (B)

The device that changes one value of AC voltage into another value does so through mutual induction between windings on a magnetic core. When alternating current flows in the primary winding, it creates a changing magnetic flux in the core, which links to the secondary winding and induces a voltage there. The voltage ratio is determined by the turns ratio between the windings, so more turns on the secondary raise the voltage (step-up) and fewer turns lower it (step-down). Because the flux must be changing, this only works with AC; steady DC would not produce an ongoing induction.

Energy is roughly conserved, so the current shifts inversely with the voltage: higher secondary voltage means lower primary current, and vice versa, aside from losses. This is why transformers are ubiquitous in power distribution and electronics power supplies.

A condenser (capacitor) stores electrical energy but doesn’t convert voltage levels; an inductor stores energy in a magnetic field and can filter or shape current, not change voltage by a fixed ratio; a rotor is a mechanical part of machines, not a voltage-transforming device.