Capacitor, or electrical condenser, device for storing an electrical charge. In its simplest form a capacitor consists of two metal plates separated by a nonconducting layer called the dielectric. When one plate is charged with electricity from a direct-current or electrostatic source, the other plate will have induced in it a charge of the opposite sign; that is, positive if the original charge is negative and negative if the charge is positive. The Leyden jar is a simple form of capacitor in which the two conducting plates are metal-foil coatings on the inside and outside of a glass bottle or jar that serves as the dielectric. The electrical size of a capacitor is its capacitance, the amount of electric charge it can hold. The charge it can hold is inside the electric field between the capacitors that happen in the dielectric. With AC, capacitors charge and discharge according to the inherent characteristics of the circuit where the capacitor is connected and this makes it useful with specifying timing synchronization in some circuits that need switching.