Which describes how energy is stored in a capacitor?

• A. Electrostatic charge
• B. Magnetic energy
• C. Chemical energy
• D. Kinetic energy

Answer: (A)

Energy storage in a capacitor comes from the electric field created by separated charges on the two plates. When a capacitor is charged, opposite charges accumulate on the facing surfaces, establishing an electric field between the plates. The work done to assemble those charges against their attraction is stored as electrostatic energy in that field. The amount of energy grows with charge or voltage, following E = 1/2 QV or E = 1/2 C V^2. This is why describing the storage as electrostatic charge best captures how a capacitor holds energy. Magnetic energy would be tied to magnetic fields around currents (inductors), chemical energy to bonds in chemicals, and kinetic energy to moving objects, none of which describe the capacitor’s stored energy.