The quality factor is , in general, defined as the ratio of resonant frequency to bandwidth. It is given by
Thus the quality factor, Q can be improved by decreasing the resistance, R or increasing the ratio of inductance to capacitance L/C.
In a series RLC circuit resonance can be obtained by varying f, that is adjusting the values of L and C. In radio receiver, capacitance is varied to tune different radio station so that resonance is obtained at the desired frequency.
Q is also a measure of the degree of sensitivity of the circuit.