In this chapter we introduce series RLC circuits for the AC case. There is much here that will be familiar from your prior studies with DC series circuits, however, there will be a few notable changes and perhaps a surprise or two lurking. The key to most of this is to remember that all computations involve vector quantities. In fact, DC can be thought of as a special case of AC; namely, the frequency drops to zero hertz causing \(X_C\) to approach an open and \(X_L\) to drop to zero. This leaves us with just resistors and scalar quantities because the phase angles in the remainder of the circuit collapse to zero for DC steady state.
Many of the solution techniques from DC analysis will be applicable here. This includes the use of Ohm's law and Kirchhoff's voltage law, along with the voltage divider rule. Generally, reactance values will need to be computed from capacitor and inductor values before the main analysis may begin. In this chapter, as in the most of the remaining chapters, we shall be concerned with determining the circuit response based on a source with a single frequency of excitation, in other words, a simple sine wave.
To clarify our analyses, we shall make considerable use of both time domain voltage plots as well as phasor diagrams.