way that cannot generally occur with resistance. Capacitors act like “negative induc-tors.” Interesting things happen when capacitors and inductors are combined, which isdiscussed in the next couple of chapters.Reactance can vary from extremely large negative values, through zero, to ex-tremely large positive values. Engineers and physicists always consider reactance to beimaginary. In the mathematical model of impedance, capacitances and inductancesmanifest themselves “perpendicularly” to resistance.The general symbol for reactance is X; this encompasses both inductive reactance(XL) and capacitive reactance (XC).Vector representation of impedanceAny impedance RjX can be represented by a complex number of the form ajb.Just let Ra and Xb.It should be easy to visualize, now, how the impedance vector changes as either Ror X, or both, are varied. If X remains constant, an increase in R will cause the vector to270 Impedance and admittance15-5The complex impedanceRX plane.