Resonant Frequency:

Resonance occurs in an AC circuit when inductive reactance and capacitive reactance are equal to one another:  X_L = X_C.    When this occurs, the total reactance, X = X_L - X_C becomes zero and the impendence is totally resistive. Since inductive reactance and capacitive reactance are both dependent on frequency, it is probable to bring a circuit to resonance by adjusting the frequency of the applied voltage.  Resonant frequency (f_Res) is the frequency at which resonance occurs, or where X_L = X_C.  Equation (8-14) is the mathematical representation for resonant frequency.

f_Res  = 1/2Π√LC                                                    (8-14)

f_Res = resonant frequency (Hz)

L = inductance (H)

C = capacitance (f)