Which component stores energy in a magnetic field?

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

Answer: (C)

Inductors store energy in a magnetic field. When current flows through a coil, a magnetic field builds up around it and a portion of the energy is stored in that field. The stored energy equals 1/2 L I^2, with L as the inductance and I as the current. This magnetic energy is why inductors resist sudden changes in current, since changing the current alters the magnetic field and the energy in it, creating a back-EMF that opposes the change. A capacitor stores energy in an electric field between its plates (1/2 C V^2), a resistor mainly dissipates energy as heat, and a transformer uses magnetic fields to transfer energy between windings rather than primarily storing it. So, the component that stores energy in a magnetic field is the inductor.