Electronics Principles V11

Clive W. Humphris

IMPEDANCE: RC Series Impedance.  

Impedance is the sum of resistance and reactance in an AC circuit, it is measured in Ohms and given the symbol Z. Impedance can be used in place of resistance when calculating AC using Ohm's Law on reactive circuits. The voltages developed across R and C (Xc) cannot be added directly as the voltage across C is at 90° to that across R.

The impedance triangle can be a useful method to graphically find the impedance Z.

The resultant impedance phase angle will be determined by the relative values of R and Xc. With the angle becoming greater as the reactance of the capacitor to the applied frequency increases.

A lagging (-) phase angle indicates a capacitive circuit.

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