Hi all, For a resonant system, there is usually a transfer of energy into another kind of energy back an forth (kinetic to potential; electric to magnetic, etc). for an LC tank or an RLC circuit, we know that the energy is transfered from as an electric field between the capacitor's plate to a magnetic field around an inductor coil. But, how come we can define a q-factor for an inductor alone? Thank you very much for your help :)
You can't. The Q-factor is a measure of how closely a real inductor comes to behaving like an ideal inductor; an ideal inductor would have an infinite Q at all frequencies but real inductors are made from resistive wire etc so there are always losses.
You can define a Q-factor for many situations where oscillation occurs. Inductors, and capacitors have a Q when are subjected to AC. It sort of is a measure of deviation from an ideal component as said.