The action of a capacitor Capacitors store charge and energy. They have many applications, including smoothing varying direct currents, electronic timing circuits and powering the memory to store information in calculators when they are switched off. A capacitor consists of two parallel conducting plates separated by an insulator.
It is a function of the geometric characteristics of the capacitor - plate separation (d) and plate area (A) - and by the permittivity (ε) of the dielectric material between the plates. Capacitance represents the efficiency of charge storage and it is measured in units of Farads (F).
The capacitor may be modeled as two conducting plates separated by a dielectric as shown on Figure 2. When a voltage v is applied across the plates, a charge +q accumulates on one plate and a charge –q on the other. Figure 2. Capacitor model capacitor plates i = dq . And thus we have, dt
Capacitors have the ability to store an electrical charge in the form of a voltage across themselves even when there is no circuit current flowing, giving them a sort of memory with large electrolytic type reservoir capacitors found in television sets, photo flashes and capacitor banks potentially storing a lethal charge.
Capacitor leakage current is an important parameter in amplifier coupling circuits or in power supply circuits, with the best choices for coupling and/or storage applications being Teflon and the other plastic capacitor types (polypropylene, polystyrene, etc) because the lower the dielectric constant, the higher the insulation resistance.
A charged capacitor can supply the energy needed to maintain the memory in a calculator or the current in a circuit when the supply voltage is too low. The amount of energy stored in a capacitor depends on: the voltage required to place this charge on the capacitor plates, i.e. the capacitance of the capacitor.