How does a capacitor store energy?

A capacitor stores energy by creating an electric field between two conductive plates separated by an insulating material, or dielectric.12

The Charging Process

Energy storage occurs through the work performed to move electric charge onto the plates. Initially, both plates are uncharged. As negative charge is moved from one plate to the other, the source must overcome the repulsion of the already negatively charged plate and the attraction of the positively charged plate. This process requires work, which is stored as potential energy within the resulting electric field.123

Energy Storage

The stored energy is equivalent to the work required to establish this field. Because the charges are attracted to each other but cannot cross the dielectric, the energy remains trapped, similar to the potential energy of a stretched spring. The total energy $W$ in joules can be expressed using the charge $Q$ and potential difference $V$ as:13

• $W=\frac{1}{2}QV$
• $W=\frac{1}{2}C{V}^2$
• $W=\frac{Q^2}{2C}$13

The energy is effectively stored in the volume between the plates, with the energy density determined by the strength of the electric field.13