Editing Input impedance (section)

{{short description|Measure of the opposition to current flow by an external electrical load}}

In [[electrical engineering]], the '''input impedance''' of an [[electrical network]] is the measure of the opposition to [[Electric current|current]] ([[Electrical_impedance|impedance]]), both static ([[Electrical resistance and conductance|resistance]]) and dynamic ([[Electrical reactance|reactance]]), into a [[Electrical load|load]] network or circuit that is ''external'' to the electrical source network. The input [[admittance]] (the [[Multiplicative inverse|reciprocal]] of impedance) is a measure of the load network's propensity to draw current. The source network is the portion of the network that transmits [[Electric power|power]], and the load network is the portion of the network that consumes power.

For an electrical property measurement instrument like an [[oscilloscope]], the instrument is a load circuit to an electrical circuit (source circuit) to be measured, so the input impedance is the impedance of the instrument seen by the circuit to be measured.

[[Image:Source and load circuit Z (2).svg|thumb|200px|The circuit to the left of the central set of open circles models the source circuit, while the circuit to the right models the connected circuit. {{math|''Z''<sub>S</sub>}} is the output impedance seen by the load, and {{math|''Z''<sub>L</sub>}} is the input impedance seen by the source.]]