6 - Resonance

Abstract

This chapter discusses various aspects of the series and parallel resonance. Series resonance has important applications in filter circuits and radio and television tuning circuits. It is found that when an RLC circuit is in a state of series resonance, the circuit behaves as a pure resistance and the inductive reactance is equal to the capacitive reactance. It is observed that if the resistance is small, the current could be very large, and the potential difference developed across the inductance and the capacitance would then be very large. It is found that as the resistance of the circuit becomes smaller, the current becomes larger and the stored energy oscillating between the capacitor and the inductor becomes much larger than the energy dissipated in the resistor. A bandpass filter is designed to allow signals at the resonant frequency and those within a band of frequencies above and below to pass from the input terminals to the output terminals. Signals at frequencies outside this band are passed at a much reduced level or not at all, and are said to be rejected. Under certain conditions the parallel RLC circuit behaves as a pure resistor because the phasors representing the circuit supply voltage and the total current drawn from the supply are in phase with each other. This condition is known as parallel resonance. The dynamic impedance of the tuned circuit is also elaborated in the chapter.