What stores energy in a magnetic field?

• A. Capacitor
• B. Inductor
• C. Resistor
• D. Transformer

Answer: (B)

Storing energy in a magnetic field happens when current flows through a coil, creating a magnetic field around it. The energy sits in that magnetic field and can be returned to the circuit as the current changes. The amount of energy stored is proportional to the inductance and the square of the current: E = 1/2 L I^2. This is what an inductor does—it stores energy in its magnetic field and resists changes in current because building or collapsing that field requires or releases energy. Capacitors store energy in electric fields between plates (E = 1/2 C V^2), so they handle electric energy rather than magnetic. Resistors dissipate energy as heat and don’t store it. A transformer uses magnetic fields to transfer energy between windings, and while magnetic fields exist there, its primary role is energy transfer rather than storage.