In pure resistance within an AC circuit the current and voltage will oscillate in phase, that is, when the current is at its maximum the voltage will also be at its maximum, hence there is no phase shift. In addition, the resistance value is not affected by the height of the frequency.
However, when there are inductors or capacitors in the circuit there will be phase difference between the current and the voltage as they will oscillate ninety degrees out of phase. Complex numbers are used to monitor both the phase and the magnitude where the resistance (R) is used in conjunction with an imaginary unit to represent reactance (X). AC resistance can be determined using an LCR meter.
Z = R + i X
Z = R + iX = R + iωL + 1/iωC
Angular frequency ω = 2 × π × f« Back