You have studied that a linear impedance is one in which the resulting current is directly
proportional to a change in the applied voltage. A nonlinear impedance is one in which the resulting
current is not directly proportional to the change in the applied voltage. View (A) of figure 1-8 illustrates
a circuit which contains a nonlinear impedance (Z), and view (B) shows its voltage-current curve.
Figure 1-8A.Nonlinear impedance circuit.
Figure 1-8B.Nonlinear impedance circuit.
As the applied voltage is varied, ammeter readings which correspond with the various voltages can
be recorded. For example, assume that 50 volts yields 0.4 milliampere (point a), 100 volts produces 1
milliampere (point b), and 150 volts causes 2.2 milliamperes (point c). Current through the nonlinear
impedance does not vary proportionally with the voltage; the chart is not a straight line. Therefore, Z is a
nonlinear impedance; that is, the current through the impedance does not faithfully follow the change in
voltage. Various combinations of voltage and current for this particular nonlinear impedance may be
obtained by use of this voltage-current curve.