Which of the following stores energy in an electric field?

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

Answer: (A)

Storing energy in an electric field happens when charges are separated so that an electric field exists between conductors. A capacitor does exactly that: its plates hold opposite charges, creating an electric field in the dielectric between them. The energy stored in that field is given by W = 1/2 C V^2, where C is the capacitance and V is the voltage across the plates. That field energy is the hallmark of a capacitor.

In contrast, an inductor stores energy in a magnetic field produced by current in a coil, with energy W = 1/2 L I^2. A resistor simply dissipates electrical energy as heat, and a diode mainly controls current flow without storing usable energy in a field. So the device that stores energy in an electric field is the capacitor.