What is a transformer?

• A. A device that stores energy in a magnetic field.
• B. A device that increases or decreases the voltage of alternating current.
• C. A device that switches DC to AC.
• D. A device that filters noise.

Answer: (B)

Transformers rely on voltage changing through magnetic coupling. When alternating current flows in the primary winding, the magnetic flux in the core changes over time and induces a voltage in the secondary winding proportional to the turns ratio. That lets the device increase or decrease the voltage of alternating current while transferring power from one circuit to another. It’s designed to transfer energy efficiently, not to store energy like a capacitor or battery; the magnetic field is a means of coupling, not a long-term storage element. Because DC doesn’t continuously change, a transformer won’t sustain induction with direct current—after the initial surge, there’s no changing flux to keep inducing voltage. The core is usually laminated to minimize eddy currents, and the main practical considerations are the turns ratio (which sets the voltage change) and the associated losses in windings and the core.