Editing Electrical impedance (section)

=== Ohm's law ===
[[File:General AC circuit.svg|thumb|right|165px|An AC supply applying a voltage <math>V</math>, across a [[Electrical load|load]] <math>Z</math>, driving a current <math>I</math>]]
{{Main|Ohm's law}}

The meaning of electrical impedance can be understood by substituting it into Ohm's law.<ref>[http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html AC Ohm's law], Hyperphysics</ref><ref name=HH1>{{cite book |last=Horowitz |first=Paul |author2=Hill, Winfield |title=The Art of Electronics |year=1989 |publisher=Cambridge University Press |isbn=978-0-521-37095-0 |pages=[https://archive.org/details/artofelectronics00horo/page/32 32–33] |chapter=1 |chapter-url=https://archive.org/details/artofelectronics00horo |url=https://archive.org/details/artofelectronics00horo/page/32 }}</ref> Assuming a two-terminal circuit element with impedance <math>Z</math> is driven by a sinusoidal voltage or current as above, there holds  

:<math>\ V = I Z = I |Z| e^{j \arg (Z)}</math>

The magnitude of the impedance <math>|Z|</math> acts just like resistance, giving the drop in voltage amplitude across an impedance <math>Z</math> for a given current <math>I</math>. The [[phase factor]] tells us that the current lags the voltage by a phase <math>\theta = \arg(Z)</math> (i.e., in the [[time domain]], the current signal is shifted <math display="inline">\frac{\theta}{2 \pi} T</math> later with respect to the voltage signal).

Just as impedance extends Ohm's law to cover AC circuits, other results from DC circuit analysis, such as [[voltage divider|voltage division]], [[current divider|current division]], [[Thévenin's theorem]] and [[Norton's theorem]], can also be extended to AC circuits by replacing resistance with impedance.