Electrical Engineering ⇒ Topic : Impedance-frequency curve

Impedance-frequency curve. If we plot impedance-frequency graph for a parallel circuit shown in Fig. a (i), the shape of the curve will be as shown in Fig. (b). Note that the impedance of the circuit is maximum at resonance. As the frequency changes from resonance, the circuit impedance decreases very rapidly. This behaviour can be explained as follows. For frequencies below resonance, the capacitive reactance will he higher and thus *more current will flow through the coil

                                                                    figure (a)

This causes the line current to lag behind the applied voltage and the circuit appears inductive. For frequencies above resonance, inductive reactance is higher and more current will flow through the capacitor. Consequently, line current leads the applied voltage and circuit appears capacitive. In either case, the circuit impedance is far less than its value at resonance

                                                                            figure (b)