Figure illustrates variation of impedance Z, inductive reactance XL and capacitive reactance XC with frequency. At resonance XL = XC 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