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Re: [Phys-l] Reference needed

At 10:50 AM 8/19/2006, you wrote:
.... the
correct matching termination for a lossless transmission circuit is a
resistance with value \sqrt{L/C}. Feynman derives this result in a model
of lumped L-C circuit elements (II-22-12), although he doesn't tell us
that he's really modeling a transmission line circuit. I'm looking for
the classical derivation of this result.
I will be discussing Feynman's derivation, which has generated
some unnecessary controversy at the Feynman Festival at U. Md, starting on
8/25. The controversy arises from disbelief that a circuit of purely
reactive elements can look resistive at low frequencies. The DC
resistance of the circuit is just the termination value referred to above.
It doesn't seem to be in Jackson's or Schwinger's texts. If
someone has a text on transmission lines, it might be there.
Regards,
Jack

Although not responsive to Jack's question, I want to assert that
a circuit of purely reactive elements does not look resistive at
low frequencies. It is certainly true that a long transmission line
has a ratio of voltage to current at intermediate points which
behaves like a resistance of that value (called the characteristic
impedance) for a time period equal to the transmission time
for traversing that line both ways. After that time - i.e. in the
low frequency limit, the line can look capacitive, inductive or
resistive at the near end, depending on the value of the
terminating resistor at the far end, if any.



Brian Whatcott Altus OK Eureka!