13.4: Resistance and Inductance in Series
( \newcommand{\kernel}{\mathrm{null}\,}\)
The impedance is just the sum of the resistance of the resistor and the impedance of the inductor:
Z=R+jlω.
Thus the impedance is a complex number, whose real part Ris the resistance and whose imaginary part Lω is the reactance. For a pure resistance, the impedance is real, and V and I are in phase. For a pure inductance, the impedance is imaginary (reactive), and there is a 90o phase difference between V and I.
The voltage and current are related by
V=IZ=(R+jLω)I.
Those who are familiar with complex numbers will see that this means that V leads on I, not by 90o, but by the argument of the complex impedance, namely tan−1(Lω/R). Further the ratio of the peak (or RMS) voltage to the peak (or RMS) current is equal to the modulus of the impedance, namely √R2+L2ω2.