Electrical Communication is a free textbook on the basics of communication technology. See the editorial for more information....

# Capacitance

The definition of capacitance of most value in communication is1 "the property of an electric system comprising insulated conductors and associated dielectrics which determines, for a given rate of change of potential differences between the conductors, the displacement currents in the system. Thus in a system of two conductors only

where C is the capacitance, i the displacement current, and e the potential difference between the conductors." The usual units are amperes, farads, and volts per second.

Equation 9 is in terms of instantaneous values. For steady-state effective values this equation can be written

In these equations I is the magnitude of the effective value of the current in amperes, Ec is the magnitude of the effective value of voltage across the condenser in volts, and f is in cycles per second. The voltage EC lags the current I by 90°. This equation assumes that capacitance only exists in the circuit,

Last Update: 2011-05-14