On my text book, there are several definition given for this Q factor. 1) 2 pi * maximum energy stored in reactive element / energy dissipated in a period 2)resonance frequency (in terms of ω) / band width 3)Q = 1/(2 * damping factor) I have tried a couple of random circuits, and its seems not all of them are correct for arbitrary circuit. (Some o them may only true for simple RLC series of parallel). May I ask which statement is always true? My text book also says resonant frequency = natural frequency *(1-2*zeta^2) where zeta is damping factor and undamped natural frequency is = natural frequency *(1-*zeta^2) where zeta is damping factor Are these true for RLC series only?? Thank you!