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Capacitance

refers to the ability of a device to store energy in the form of an electrostatic field. In its simplest form, a capacitor is a pair of parallel plates spaced apart with a dielectric material between them. Coax cables have a certain capacitance per foot. The dielectric materials in a cable affect the capacitance of the cable. If two cables are identical in geometry, the cable with the higher dielectric constant insulator will have the higher capacitance per foot and, thus, the lower impedance. The standard unit of capacitance is the farad, abbreviated F. This is a large unit; more common units are the microfarad, abbreviated µF (1 µF = 10-6 F) and the picofarad, abbreviated pF (1 pF = 10-12 F). The reactance of a capacitor decreases as frequency increases.     XC = 1/(2πfC), where XC = capacitive reactance f=frequency and C=capacitance