Alternating Current (AC) Circuit Characteristics

The characteristics of an a.c. circuit depend on which of the elements Resistance ( R ), Inductance ( L ) and Capacitance ( C ) are present, and whether they are connected in series or parallel.

For a purely resistive circuit, the voltage is in phase with the current i.e. the power factor of the circuit is 1
For a purely inductive circuit, the current lags the voltage by 90° i.e. the power factor is 0
For a purely capacitive circuit, the current leads the voltage by 90° i.e. the power factor is 0

Thus, for any combination of elements R, L and C, the overall power factor of the circuit i.e. whether the current leads or lags the voltage, and by what amount, depends on whether the resultant reactance of the circuit is inductive, capacitive or zero.
Click on the hyperlinks below to get a better understanding on how the voltage and current phasors vary in simple series circuits: