Capacitors store energy in which type of field?

• A. Electric field
• B. Magnetic field
• C. Thermal field
• D. Nuclear field

Answer: (A)

Capacitors store energy in the electric field between their plates when a voltage is applied. The charges on the plates create an electric field in the dielectric that fills the space between them, and the energy sits in that field rather than in the metal itself. The amount of energy stored is given by W = 1/2 C V^2, and the energy density in the field is u = 1/2 ε E^2, with E = V/d for simple plate arrangements and C = εA/d depending on geometry and dielectric. This electric-field storage is what distinguishes capacitors from devices that rely on magnetic fields (like inductors), while thermal or nuclear fields aren’t the mechanism by which a capacitor holds energy.