Impedance vs Resistance

digipony

Just wondering here... What is the difference between impedance and resistance? Is resistance typically used to describe the nature of a circuit element, while impedance is of an entire circuit? I have looked up the definitions for both, and I just don't see the difference between them. Thanks!

davenn

really basically...

impedance is used in an AC circuit ie .... resistance to an AC current
impedance is determined from the inductive and capacitive reactances

resistance is used in a DC circuit .... resistance to a DC current

look up
Characheristic Impedance
Inductive Reactance and
Capacitive Reactance

cheers
Dave

Khashishi

Impedance rolls together resistance, inductance, and capacitance into one complex value.

Naty1

http://en.wikipedia.org/wiki/Electrical_impedence

Next line in wikipedia:

This statement is not quite correct.....in a steady state condition, this is true, but when DC is initially turned on...or shut off....there ARE reactance effects.

This is a nice/accurate synopsis from the above source:
"There are an additional two impeding mechanisms to be taken into account in AC circuits: the induction of voltages in conductors self-induced by the magnetic fields of currents (inductance), and the electrostatic storage of charge induced by voltages between conductors (capacitance). "

Studiot

There is one more difference not so far mentioned.

Inductance comes in two flavours.

Self inductance
Mutual inductance

The contribution of inductance to impedance refers only to the former.

sophiecentaur

Even a network of pure resistors can have a similar effect, though; the voltage across one of the resistors can be a scaled version of the voltage across another resistor.
Mutual Impedance is a more general term for the relationship between the volts across one element of a circuit / structure and the current passing through another - see the theory of multiple element antennae.