Which component stores energy in a magnetic field?

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

Answer: (C)

Storing energy in a magnetic field is what an inductor does. When current flows through its coil, a magnetic field forms around the windings, and energy is stored in that field. The amount stored depends on the inductance and the current, roughly described by the energy 1/2 L I^2. This magnetic storage also explains why inductors oppose sudden changes in current: increasing current builds a stronger magnetic field (and more stored energy), while a decrease lets the field collapse and can release energy back into the circuit. Capacitors store energy in electric fields between plates; resistors simply convert energy to heat; diodes don’t store energy in a magnetic field during normal operation. So the component that stores energy in a magnetic field is the inductor.