# Introduction

Any system having at least a pair of complex conjugate poles has a natural frequency of oscillation. If the frequency of the system driving force coincides with the natural frequency of oscillation, the system resonates and the system response becomes maximum. This phenomenon is known as â€˜resonanceâ€™ and the frequency at which this phenomenon occurs is known as â€˜resonant frequencyâ€™.

In electrical systems, resonance occurs when the system contains at least one inductor and one capacitor. In this system, the phenomenon of cancellation of reactances when inductor and capacitor are in series or cancellation of susceptances when they are in parallel, is termed as resonance. The circuit under resonance is purely resistive in nature and is termed as â€˜resonant circuitâ€™ or â€˜tuned circuitâ€™.