# clarification of resistance and impedance

Discussion in 'General Electronics Chat' started by james7701, Feb 15, 2016.

1. ### james7701 Thread Starter New Member

Jan 5, 2016
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0
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?

Aug 21, 2008
2,756
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YES!

3. ### james7701 Thread Starter New Member

Jan 5, 2016
28
0
could resistance only be present in DC circuits and impedance present in AC circuits? or they both appear where resistors and inductors are?

4. ### AnalogKid Distinguished Member

Aug 1, 2013
4,685
1,297
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

5. ### crutschow Expert

Mar 14, 2008
13,475
3,362
Reactive impedances doesn't appear in DC circuits, so only resistance is considered.