Impedance vs Resistance: Understanding the Distinction in Circuit Elements

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Discussion Overview

The discussion centers on the differences between impedance and resistance in electrical circuits, exploring their definitions, applications in AC and DC circuits, and the implications of inductance and capacitance. Participants examine the conceptual distinctions and technical nuances related to these circuit elements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the difference between impedance and resistance, suggesting that resistance describes individual circuit elements while impedance pertains to entire circuits.
  • Another participant states that impedance applies to AC circuits and is influenced by inductive and capacitive reactances, whereas resistance is relevant for DC circuits.
  • A participant notes that impedance combines resistance, inductance, and capacitance into a complex value.
  • It is mentioned that electrical impedance measures the opposition to current in AC circuits and includes both magnitude and phase, unlike resistance, which has only magnitude.
  • A later reply challenges a statement about the distinction between impedance and resistance in DC circuits, asserting that reactance effects occur when DC is turned on or off.
  • One participant introduces the concept of self and mutual inductance, indicating that impedance only considers self-inductance.
  • Another participant elaborates on mutual impedance, relating it to the relationship between voltage across one circuit element and current through another, particularly in multiple element antenna theory.

Areas of Agreement / Disagreement

Participants express differing views on the definitions and implications of impedance and resistance, with no consensus reached on the nuances of these concepts.

Contextual Notes

Some statements rely on specific conditions, such as the behavior of circuits under AC versus DC, and the definitions of inductance types, which may not be universally agreed upon.

digipony
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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!
 
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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
 
Impedance rolls together resistance, inductance, and capacitance into one complex value.
 
Electrical impedance is the measure of the opposition that a circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current (AC) circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude.

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

Next line in wikipedia:

When a circuit is driven with direct current (DC), there is no distinction between impedance and resistance...

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). "
 
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.
 
Studiot said:
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.

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.
 

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