电容器 Capacitor
A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator).When a potential difference (voltage) exists across the conductors,an electric field is present in the dielectric.This field stores energy and produces a mechanical force between the conductors.The effect is greatest when there is a narrow separation between large areas of conductor,hence capacitor conductors are often called plates.
An ideal capacitor is characterized by a single constant value,capacitance,which is measured in farads.This is the ratio of the electric charge on each conductor to the potential difference between them.In practice,the dielectric between the plates passes a small amount of leakage current.The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage.
Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass,to filter out interference,to smooth the output of power supplies,and for many other purposes.They are used in resonant circuits in radio frequency equipment to select particular frequencies from a signal with many frequencies.