# Relationship between impedance and resistance

### Electrical impedance - Wikipedia

The Difference Between Resistance and Impedance is explained below keeping in mind the various factors like the basic definition, type of. IMPEDANCE Basic AC Reactive Components where Z = impedance (W) R = resistance (W) X = net reactance (W) The relationship between resistance. Impedance, measured in Ohms, is the effective resistance to current flow difference between the current and the voltage when using an AC resistance as the.

To make the calculations simpler, we use complex numbers to express impedance. In that case, we only have resistance and no reactance. It's not wrong to say that a purely resistive load has impedance, because impedance consists of resistance and reactance, but it seems that over time the term impedance started to imply that there is some reactance.

Another problem with the term impedance it that it is mostly used for AC circuits and for some reason people usually get exposed to DC circuits first.

The reason why impedance isn't used for DC circuits is because of the nature of reactance. Basically for reactance, we have 3 cases: When reactance is zero, when it is positive, and when it is negative. With DC current the frequency is zero and therefore the imaginary part of impedance is zero too, giving us only resistance. Because the resistance is often considerably lower than reactance an ideal coil is considered to have zero resistance and in DC circuits is a short.

In DC circuits as the frequency approaches zero, the reactance approaches infinity and for that reason ideal capacitors are modeled as open circuit in DC circuits.

## Difference Between Resistance and Impedance

There's also the inverse of impedance called admittance. Basically each part of the circuit acts as a combination of a resistor, inductor and a capacitor.

It is possible to calculate inductance of a piece of wire for example using Biot-Savart law or Gauss's law. Capacitance among other things may be calculated using Gauss's law for electric field or Coulomb's law. However, if a very high frequency is put across that capacitor a signal that has a voltage which is changing very quickly back and forththe capacitor will look like a short circuit. The capacitor has a reactance which is inversely proportional to frequency. An inductor has a reactance which is directly proportional to frequency -- DC flows through easily while high-frequency AC is stopped.

### Review of R, X, and Z | Reactance And Impedance -- R, L, And C | Electronics Textbook

Impedance is the total contribution of both -- resistance and reactance. This is important for AC analysis and design. Power has to be given in terms of resistive power and reactive power. Resistive power actually burns off energy into heat while reactive power simply stores energy in E-fields and B-fields.

Often you'll hear about the 'impedance' of transmission lines, like the cables which run between components of your stereo system, and impedance of things like speakers. You'll also hear that it is important to match these or else you'll get reflection.

## What is the difference between resistance and impedance?

This is a much more complicated subject, which a few answers have commented on in recent questions about light and its speed. However, what I want to mention is that when you hear about the impedance of a transmission line, like speaker cable or an antenna or coaxial cable or anything else, this does not represent energy which is "burned off" in the cable.

This has to do with how energy is stored in the cable as it propagates down it.

The cable does not well, in reality it does, but assume the lossless case for simplicity get hotter as a signal travels down it. It is not proper to think of a 'ohm cable' as a ohm 'resistor.

Note that impedance and reactance are both given in units of 'ohms' just like resistance. Capacitance is measured in Farads and inductance in Henries, and these relate to impedance, but they are not measures of impedance.

### Figure 5 Relationship Between Resistance, Reactance, and Impedance

As I said, the impedance of a capacitor is inversely proportional to its capacitance and the impedance of an inductor directly proportional to its inductance. This may sound a little abstract. Impedance really is an abstraction of things that are far more complicated things like time constants and rise times that electrical engineers have to constantly consider. The idea of 'impedance' allows for many of these things to be wrapped up into one subject so that they are easier to communicate. The short answer is -- impedance includes reactance, and reactance includes effects which vary with frequency due to inductance and capacitance.