# clarification of resistance and impedance

#### james7701

Joined Jan 5, 2016
37
In DC circuits resistance is the opposition (restrictions )to the flow of current
In AC circuits impedance is the measures of opposition (restrictions )of current...

did i get this short definition correct?

#### DickCappels

Joined Aug 21, 2008
6,003

#### james7701

Joined Jan 5, 2016
37
could resistance only be present in DC circuits and impedance present in AC circuits? or they both appear where resistors and inductors are?

#### AnalogKid

Joined Aug 1, 2013
8,209
Both.

Everything has an impedance (we'll leave out superconductors for now), because all electronic components have some resistance, inductance, and capacitance. A "pure" resistance has that value at all frequencies. The reactance of an inductor and capacitor vary with frequency. At 0 Hz (DC), the reactance of a pure inductor goes to zero ohms, and at infinite frequency it goes to infinity. So an inductor appears as a short circuit at DC and an open circuit at infinite frequency. A capacitor is the opposite, a short circuit at infinite frequency and an open circuit at DC. In between those extremes, reactive components have an impedance based on their equations.

ak

#### crutschow

Joined Mar 14, 2008
23,722
Reactive impedances doesn't appear in DC circuits, so only resistance is considered.