A capacitor is a device that can store electrical energy in an electric field. Its capacitance (C) is directly proportional to the permittivity of free space and the area of the conductive plates, and inversely proportional to the distance between the plates. The charge (Q) stored on a capacitor is directly proportional to its capacitance (C) and voltage (V). The energy (W) stored in a capacitor is equal to one-half the capacitance (C) multiplied by the square of the voltage (V). Capacitors can be connected in series or parallel configurations, which affects how charge and voltage are distributed across the capacitors.