A capacitor is a passive component that stores electrical energy, widely used in common electrical devices and circuits. They are used to block direct current while allowing alternating current to pass, smooth the output of power supplies, stabilize voltage, and stabilize power flow.
Capacitors work by storing positive and negative charges on opposite sides of an insulating dielectric. The capacitor can continue to accept more charge until it reaches capacitance, or the point at which any additional electrons that try to join are repelled. If a complete path in the circuit is created, the capacitor will discharge.
Capacitors come in a wide variety of sizes and types, often differentiated by the type of dielectric used and the application they are designed for. Ceramic, aluminum and tantalum electrolytic, glass, oxides, even paper can be used as the dielectric. The type and size often determine max capacitance and how the capacitor is used. Common applications include energy storage, power factor correction, and motor starting.