What term describes a passive two-terminal component that stores energy in a magnetic field when current flows through it?

• A. Hydraulic reservoir
• B. Heat exchange
• C. Psi
• D. Coil inductor

Answer: (D)

Energy storage in a magnetic field produced by current in a coil describes an inductor, a passive two-terminal component. An inductor stores energy as the magnetic field around its windings, with the stored energy given by E = 1/2 L I^2. It also resists changes in current, producing a voltage v = L di/dt as the current changes. This magnetic-field storage makes inductors essential in filters, timing circuits, and power electronics.

Hydraulic reservoir is for fluids, not electricity; heat exchange involves transferring heat, not storing magnetic energy; psi is a unit of pressure. A capacitor also stores energy, but in an electric field between plates, not a magnetic field.