Impedance Curve:

Figure illustrates variation of impedance Z, inductive reactance X_L and capacitive reactance X_C with frequency. At resonance X_L = X_C and Z = R.

Figure: Impedance Curve

Angle φ (between voltage and current) is given by

φ= tan^-1  ( X _L - X c ) /R

Here, φ is known as the power factor angle. Figure illustrates the variation of φ with frequency.

At frequencies below ω₀ the capacitive reactance is greater than the inductive reactance and the angle of the impedance is -ve. If the resistance is low, the angle alters more quickly with frequency as illustrated in Figure. As ω approaches zero the angle of Z approaches - 90.

Figure: Angle Curve