In a universal AC series circuit consisting of series resistors, inductors, and capacitors, the impedance of the circuit is given by the following equation:

Now, if the inductance reactance XL is equal to the capacitance reactance XC, the resulting reactance is zero, and the impedance of the circuit is equal to the Ohmic resistance, i.e. Z=R ohm. Current I=V/R, and it is same to V.In this case, the circuit is in a resonant or series resonant state. At this stage, the current is maximum because the impedance is minimum.

Resonance is the result of applying a frequency that is consistent with the natural frequency of the circuit. In this case, the voltage across the coil and capacitor may be many times greater than the normal applied voltage. Therefore, it may lead to equipment malfunction.

Due to the voltage (V L) across the inductor being equal to the voltage (V C) across the capacitor, the circuit is in series resonance. The frequency at which the circuit accepts resonance. Therefore, it is also known as a receiver circuit. The overall performance of the circuit is purely resistive, as the inductive effect of the circuit is completely offset by the capacitive effect.

Resonance frequency (f r):

The specific frequency value at which resonance occurs in an R-L-C series circuit is called the resonance frequency. Usually represented by f.

Its value can be obtained as follows: