12.1 INTRODUCTION

A two-terminal network, in general, offers a complex impedance consisting
of resistive and reactive components. If a sinusoidal voltage is applied to such
a network, the current is then out of phase with the applied voltage. Under
special circumstances, however, the impedance offered by the network is
purely resistive. The phenomenon is called resonance and the frequency of
the applied signal at that resonance is called the frequency of resonance or
resonant frequency. The nature of resonance depends upon whether the
inductance and the capacitance are in series or in parallel. Accordingly, we
classify the resonant circuits into the following two categories:

(i) Series resonant circuit, and,
(ii) Parallel resonant circuit.