Which of the following is a coil of wire that stores energy in a magnetic field?

• A. Resistors
• B. Inductors
• C. Capacitors
• D. Diodes

Answer: (B)

Inductors store energy in a magnetic field created by current flowing through a coil. The energy depends on the inductance and the current, following E = 1/2 L I^2, and the coil resists changes in current because a changing current builds or collapses a magnetic field that induces an opposing voltage (V = L di/dt). This magnetic energy storage is what makes inductors useful in filtering, timing, and power storage in circuits. Resistors convert electrical energy to heat and don’t store energy in a field. Capacitors store energy in an electric field between plates, not a magnetic one. Diodes control current direction and don’t store energy in a magnetic field.