This appendix is added for those readers who might need it for other application than electric circuits, such as in communications. For parallel and series circuits a quality factor Q can be defined using the values of the three components. Q is a ratio; so it is a number without any unit. Here R is the resistance of a resistor that is part of the RLC and must not be confused with the internal resistance of a coil as an inductor.
For a parallel RLC circuit the quality is
At the resonance frequency, for which XC = XL, C can be substituted in terms of L and Equation F.1 assumes the form
Because XC = XL, Q can also be written as Q =
For a series RLC the quality is XC