Capacitive reactance, indicated by XC, is the opposition of a capacitance to the flow of sine-wave alternating current.
Reactance XC is measured in ohms because it limits the current to the value V/XC. With V in volts and XC in ohms, I is in amperes.
XC = 1/(2πfC ). With f in hertz and C in farads, XC is in ohms.
For the same value of capacitance, XC decreases when the frequency increases.
For the same frequency, XC decreases when the capacitance increases.
With XC and f known, the capacitance C = 1 (2πfXC).
With XC and C known, the frequency f = 1 (2πfXC).
The total XC of capacitive reactances in series equals the sum of the individual values, as for series resistances. The series reactances have the same current. The voltage across each reactance is IXC.
The combined reactance of parallel capacitive reactances, is calculated by the reciprocal formula, as for parallel resistances. Each branch current is V/XC. The total line current is the sum of the individual branch currents.
Table 17–3 summarizes the differences between C and XC.
