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### Network # Impedance

#### Bluepoint SEO

Jul 28, 2016
88
What's the difference between impedance and resistance? I have a gut feeling impedance is more to do with the blocking effect of inductors? But I could be thinking bs.

#### Minder

Apr 24, 2015
3,268
In the absence of any text books, Let Google be your friend, the basic three are resistance , capacitance, inductance.
Bone up on these three and their characteristics in AC & DC application.
M.

• Arouse1973 and hevans1944

#### Minder

Apr 24, 2015
3,268
What I suggest is before going on to Transistors and IC's etc is to get the basics down first and this usually entails the three R,C,L and the effects when used in conjunction with DC and AC power.
These are the three basic components you are going to see in just about every circuit afterwards.
M.

• Arouse1973 and hevans1944

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,739
What's the difference between impedance and resistance? I have a gut feeling impedance is more to do with the blocking effect of inductors? But I could be thinking bs.
You are thinking bs. Do as @Minder suggested and learn what resistors, capacitors, and inductors DO and HOW they do it. Some simple algebra and trigonometry will be involved at first, but you can go much deeper down the rabbit hole with a little calculus and a simple differential equation or two.

To answer your question: resistance and impedance are related quantities, both measured in ohms. Impedance however is a complex number composed of a real resistive component and an imaginary reactive component. Complex number arithmetic is required to analyze circuits that include parts having impedance. In a circuit, only the resistive component dissipates real power (manifested as heat). The voltage across the reactive component is ninety degrees out of phase with the current through the reactive component. As a result, the product of the reactive voltage and reactive current averages to zero over complete cycles of the applied waveform.

Reactance (and therefore impedance) is a function of frequency, increasing with increasing frequency for inductors and decreasing with increasing frequency for capacitors. Reactance is always associated with devices that store energy in either an electromagnetic field (inductor) or an electrostatic field (capacitor), but reactance has no meaning at zero frequency or DC. An ideal inductor has no series resistance and zero "reactance" at DC. An ideal capacitor has no parallel (leakage) resistance and infinite "reactance" at DC. Neither ideal inductors nor ideal capacitors actually exist, although a super-conducting coil comes close and a vacuum capacitor in outer space also comes close. You are not likely to encounter either in the near future.

All real electronic components have resistance, capacitance, and inductance associated with them. Most inductors are characterized by their inductance and the series resistance of the wire used to wind the inductor, but there is also distributed capacitance associated with the inductor. This may or may not be important to circuit analysis, depending on the frequencies being considered. Similarly, most capacitors are characterized by the capacitance and the parallel or leakage resistance across their two terminals, but there is also inductance and series resistance of the wires connected to the capacitor. And again, this may or may not be important to circuit analysis, depending on the frequencies being considered.

You can calculate impedance graphically if you know the resistance and reactance. Positive reactance is associated with inductive reactance and negative reactance is associated with capacitive reactance. Plot either of these on the Y-axis of linear Cartesian coordinate graph paper. Plot resistance on the positive X-Axis. Draw a horizontal line, parallel to the X-axis, through the point that represents reactance. Draw a vertical line, parallel to the Y-Axis, through the point that represents resistance. Where these two lines intersect, mark a point. The distance of this point from the origin (Y = 0 and X = 0) is the magnitude of the impedance. You can also solve for impedance using trigonometry applied to the graph you just made.

Now go Google and read some technical articles.

#### Sunnysky

Jul 15, 2016
506
Impedance includes the possibility of phase shift between voltage and current , or a time lag of either current (C ) or voltage (L)
Pure Resistance is always in phase.

Yet at sufficiently high f, all passive parts , R, L, C have imperfections. Longs leads and coils have L and R, then stray parallel capacitance while C will have a series L where at some point the impedance will be equal but opposite phase. What do you think happens there?

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