StellarA capacitor is a device that stores electric charge and electric potential energy. The simplest model is two conductors separated by an insulating gap. When one conductor holds positive charge and the other holds negative charge, an electric field exists between them, and energy is stored in that field. The amount of charge a capacitor stores per unit potential difference is called its capacitance, defined by
where Q is the magnitude of charge on either plate and Δ V is the potential difference across the capacitor. A larger capacitance means more charge can be stored for the same voltage.
For a parallel-plate capacitor, capacitance depends on geometry: larger plate area increases capacitance, while greater plate separation decreases it. Once a capacitor is charged, it also stores energy. The energy can be written as
These equivalent forms are useful in different situations. Physically, the stored energy comes from the work required to separate charge and build the electric field between the plates. This makes capacitors important in circuits, energy storage, and transient electrical behavior.