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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    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?
     
  2. DickCappels

    Moderator

    Aug 21, 2008
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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
    4,546
    1,252
    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
    13,056
    3,245
    Reactive impedances doesn't appear in DC circuits, so only resistance is considered.
     
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