Impedance

Ok, what the heck is impedance?? Please try to use small words because I am an idiot. I thought it was related to inductance, but that was probably a good joke for whoever knows better. I just want to figure out what it means.

Impedance - imagine a plot where resistance on the horizontal axis (resistance from real resistance) and inductive reactance (in units of ohms) on the vertical axis (look up equation for an inductor). The impedence (Z) is the distance from the plot origin to the point on the plot where inductive reactance meets resistance. You'll need to a ruler to measure it on your graph or Pythagorean's theorem to calculate it. If real resistance is zero, impedence is equal to inductive reactance. If there is no significant inductive reactance at the frequency of interest, then impedance equals simple dc resistance.
Once you master that, add a capacitor and calculate again...
Read this - **broken link removed**

gophert said:

Impedance - imagine a plot where resistance on the horizontal axis (resistance from real resistance) and inductive reactance (in units of ohms) on the vertical axis (look up equation for an inductor). The impedence (Z) is the distance from the plot origin to the point on the plot where inductive reactance meets resistance. You'll need to a ruler to measure it on your graph or Pythagorean's theorem to calculate it. If real resistance is zero, impedence is equal to inductive reactance. If there is no significant inductive reactance at the frequency of interest, then impedance equals simple dc resistance.

Click to expand...

interesting thank you

I added a bit to the end

Impedance is the restriction to current flow of a signal as determined by the resistors, capacitors, inductors in the circuit.
It can vary with frequency and there may be a phase-shift between the input and output for AC signals.
For a pure resistor circuit the impedance is its resistance.

This is further explained by the information gophert provided.

Impedance can be thought of as resistance that is frequency-dependant, called Reactance.

eg. A perfect capacitor has infinite impedance at DC, but will pass some amount of AC, depending on the frequency and capacitor value.

An inductor - coil, choke, solenoid, motor or loudspeaker windings etc. - is just a piece of wire at DC, but appears higher resistance as the frequency increases, as energy has to be stored and recovered in the magnetic field around it as that changes.

Think of that as the electronic equivalent of a flywheel; the bigger it is, the harder it is & longer it takes to change the "speed" of current flow through it.

The equivalent resistance (reactance) of a capacitor or inductor at any particular frequency can be calculated by simple equations:

For a capacitor, "Two pi F C":
2 * pi * F* C
[with F in Hz and C in Farads].

For an inductor, "One over two pi F L":
1 / (2 * pi * F * L)
[With L in Henries].

More info here:

rjenkinsgb said:

Impedance can be thought of as resistance that is frequency-dependant, called Reactance.

Click to expand...

Not exactly. Impedance is the vector addition of capacitive reactance, inductive reactance and frequency independent resistance where the reactance calculations or measurements are done at a particular frequency.