Definition of Impedance
Almost everyone has heard of Ohm’s Law, which relates voltage to electrical current flow in an electrical circuit.
E = I · R
R is the resistance of an electrical circuit. It has units of ohms. A resistance has the important property that its value is independent of the frequency of an alternating current (AC) signal applied to it.
Often current flow depends on AC frequency. In this case a more general form of Ohm’s Law is used.
E = I · Z
Z is called the impedance of the circuit. It is a complex number with a magnitude expressed in ohms. Unlike a resistance, an impedance can change value with frequency.
The complex impedance of a reference electrode is often dominated by resistive effects. For this reason, the terms resistance and impedance are often used interchangeably when discussing reference electrode impedance.
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Last revised on Thursday, August 30, 2007