What is the unit of impedance?

Answer 1

Impedance "Z" is measured in Ohms, same as resistance. The only difference is that this form of resistance is frequency dependent where induction or capacitances are involved. Z = sqr(R2+X2) and in its complex from Z = R +jX where j = sqr(-1). The classical apparent power (V x I) will not apply as well as it apply in DC circuits. It would rather be in the form of P = Power Factor x V x I where Power Factor is PF= cos (angle) and angle = tan-1(X/R) since there is a phase shift between voltage and current due to the reactance (X) of the load, for inductive reactance the current lag, for capacitive reactances the current lead.

I only use X as a general form of reactance, but normally reactance will either be:

XL = 2 x Pi x f x L for inductive components

or

Xc = 1 / (2 x Pi x f x C) for capacitive components

X, XL or Xc is also in ohms

Impedance is Z and measured in Ohms and the same series - parallel laws apply as with resistances.

When do you need to worry about impedance? when you work with alternating currents and not DC. When there are possible induction or capacitance involved which is the case most of the time.

Answer 2

ohms.