Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
Tesla list wrote:
As far as I know resistance and impedance are the same.
Not exactly.
Resistance is the real part of impedance. Reactance is the imaginary part.
You could have a "ground connection" that has zero ohms resistance,
yet have a 1000 ohm impedance (i.e. an inductor of some sort), and
that's why the distinction is important.
I prefer to avoid the abstraction of "imaginary" resistance, that
is not a real thing, but just a mathematical trick to do the
calculations, meaning that, if the voltage is a sinusoid, the
current is a cosinusoid, at +/- 90 degrees with the voltage.
Even so, this works only for sinusoidal signals (and periodical
signals, if you decompose them in Fourier series).
A resistor has always the same impedance, for any frequency.
A capacitor has an impedance proportional to the inverse of
the frequency, so it blocks DC and allows the passage of currents
that vary at high frequency.
An inductor has an impedance that is proportional to the
frequency, so it is a short-circuit at DC and blocks vast-varying
currents.