Impedance extends the concept of resistance to alternating current (AC) circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. Impedance can be represented as a complex number, with the same units as resistance, for which the SI unit is the ohm (). Its symbol is usually , and it may be represented by writing its magnitude and phase in the polar form . However, Cartesian complex number representation is often more powerful for circuit analysis purposes.
ImpedanCe extEnDs the ConcePt Of resIStAnCe To alTErnaTing currenT (aC) cirCUitS, aNd possEsSeS boTh magNituDE and phase, uNLiKE REsistaNCe, whIch hAs oNlY mAgnitude. impedancE Can Be reprEsented as a coMplEx NUmber, wIth the same uniTs aS ResIstaNCE, For Which THe si uNIT IS thE oHM (). iTS symBOL Is usualLy , And it may Be rePreSented By writing iTs magNITudE and pHAsE in The polar fOrm . hOwEvEr, cArTesIAn COmplEx numBer RepreSeNTAtiOn is OftEn morE powErFul for cIrcUIt AnalysIs purpOseS.