By hvhipot 
It is said that series resonance (also known as frequency conversion resonance) occurs in a series LCR circuit when the capacitive reactance is equal to the inductive reactance at the maximum current allowed by the AC power supply at a given frequency.
The current (1) in a series LCR circuit is given by the following equation
At high frequencies
At low frequencies
if
The impedance of the LCR circuit is the smallest, therefore the current is the largest. This frequency Fo is called series resonance.
For the determination of resonance frequency in series resonance, we have
Application of LCR Circuit
The LCR circuit allows maximum current to be generated at a specific frequency during resonance. LCR circuits are used as transmitters and receivers for wireless, television, and telephone carrier equipment.
Quality factor of resonant circuit
The quality factor or Q coefficient of a series resonant circuit is defined as the ratio of the voltage generated across the inductor or capacitor during resonance to the applied voltage (i.e., the voltage applied across R).
Q factor of inductance
Q value of capacitor