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Capacitance is the ability of an object to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related notions of capacitance: self capacitance and mutual capacitance.
In electrical engineering, electrical length is a dimensionless parameter equal to the physical length of an electrical conductor such as a cable or wire, divided by the wavelength of alternating current at a given frequency traveling through the conductor. [1] [2] [3] In other words, it is the length of the conductor measured in wavelengths.
The capacitance between the two conductors is represented by a shunt capacitor (farads per unit length). The conductance of the dielectric material separating the two conductors is represented by a shunt resistor between the signal wire and the return wire (siemens per unit length).
The signal delay of a wire or other circuit, measured as group delay or phase delay or the effective propagation delay of a digital transition, may be dominated by resistive-capacitive effects, depending on the distance and other parameters, or may alternatively be dominated by inductive, wave, and speed of light effects in other realms.
In all inductors, the parasitic capacitance will resonate with the inductance at some high frequency to make the inductor self-resonant; this is called the self-resonant frequency. Above this frequency, the inductor actually has capacitive reactance. The capacitance of the load circuit attached to the output of op amps can reduce their bandwidth.
The formula for capacitance in a parallel plate capacitor is written as C = ε A d {\displaystyle C=\varepsilon \ {\frac {A}{d}}} where A {\displaystyle A} is the area of one plate, d {\displaystyle d} is the distance between the plates, and ε {\displaystyle \varepsilon } is the permittivity of the medium between the two plates.
As a result, device admittance is frequency-dependent, and the simple electrostatic formula for capacitance, = , is not applicable. A more general definition of capacitance, encompassing electrostatic formula, is: [ 6 ]
At a distance x into the line, there is current phasor I(x) traveling through each wire, and there is a voltage difference phasor V(x) between the wires (bottom voltage minus top voltage). If Z 0 {\displaystyle Z_{0}} is the characteristic impedance of the line, then V ( x ) / I ( x ) = Z 0 {\displaystyle V(x)/I(x)=Z_{0}} for a wave moving ...