Re: The discovery of the R-C circuit.

steveu@xxxxxxxxxxx wrote:
On Oct 30, 9:49 am, Jerry Avins <j...@xxxxxxxx> wrote:
steveu wrote:
Transmission lines are characterized by series resistance R and
inductance L, and by shunt capacitance C and conductance G. (All
per
unit length.) There is no dispersion when L/C = R/G
Jerry
Wrong way round. Inductance is characterised as a transmission line
with
negligible capacitance like qualities. Capacitance is characterised
as a
transmission line with negligible inductance like qualities. The
transmission line in fundamental. The others are just twisted ways
most
engineers try to look at things.
Inductance is a transmission line? I need more explanation.

Try another perspective if you don't like that one.

Two long thin sheets of conductor, separated by a relatively thin
*** of dielectric is called a transmission line. Attach two wires
the conductor sheets, roll them up, and pot them in plastic, and
suddenly people call it a capacitor. Why is that?

If the rolled-up structure's dimensions allow wave propagation at the
frequencies at which it is used, then it is a poor capacitor indeed. If
the line -- rolled or unrolled -- is short enough, then its capacitance
dominates. We used to use short pieces if 300-ohm twin lead -- an inch
or so -- as neutralizing capacitors in triode RF amplifiers. One starts
with a piece likely to be too long, and adjusts the feedback by clipping

it shorter as needed.

Why do you think that engineers' perspectives are twisted?

Jerry

Here's a fun experiment few people ever seem to try.

Take a resistor, and the kind of capacitor which is a long strip rolled
up. Multi-layers won't work too well, as they are paralleled stack of
extremely short transmission lines. Now take a really fast sampling scope,
charge and discharge the capacitor repeatedly through the resistor, and see
if you get a smooth exponential curve, or a lot of little steps, where the
step length represents the reflection time along the transmission
line/capacitors plates and back again. The relatively short length of the
transmission line doesn't make this easy, but you can see steps if you get
it right.

The thing is that however you approach this stuff, the macroscopic view
turns out the same. When you look at what is really going on things may
look different. Draw a smooth curve through those steps, and its the
exponential curve the simplistic resistor charges a capacitor model
suggests.

Steve

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