lu6etj wrote in news:5856cdb7-211c-47d6-9b19-
:

Hello Owen, good day in Australia I hope!

Sorry, with due respect, your answer throws back the ball out of the
soccer field :)
I like poetry also but would you mind search the web for another
scientific uses of "never" word?, such as in
http://www.upscale.utoronto.ca/PVB/H...y/Entropy.html.

Of course many thanks for your time and your kind reply.


Hi Miguel,

Lastly first, your reference uses "never" in the statement of a law of
physics. That might be a safer place to use it than your typical ham
assertions like "a non-resonant antenna is never going to work as good as
a resonant one".

I am not sure what "throws the ball out of field". Is it the misuse of
Thevenin equivalent circuits?

I tempted you to an exercise. In case you didn't try it, try this one.

I have three ideal components, a 1000V voltage generator, a 999.5 ohm
resistor, and a 1 ohm resistor, all in series. They are in a black box,
and both ends of the 1 ohm resistor are bought out to two terminals on
the black box. It is a trivial exercise to show that load that will
develop the most power is approximately 1 ohms. At that point, the load
voltage is 0.5V, and load power is 0.25W. Efficiency of the system (ie
Pout/Pin) is 0.25/1000=0.025%. The o/c voltage is approximately 1V and
internal dissipation is approximately 1000W, the s/c current is
approximately 1A and internal dissipation is approximately 1000W.

I have another black box with a 1.0005V generator and a series resistance
of 0.999000 ohms bought out to its two terminals. It produces exactly
the same o/c current, but with internal dissipation of 0W, exactly the
same s/c current with internal dissipation of approximately 1W, maximum
power of approximately 0.25W in an approximately 1 ohm load for system
efficiency of 50%.

Both of these networks have the same Thevenin equivalent circuit (in fact
one is the equivalent circuit), they produce the same load current, load
power, load voltage on the same load impedance, but their internal
dissipation and efficiency is quite different.

The Thevenin equivalent circuit cannot be used to explain the internal
dissipation or efficiency of a source network, but it can be used the
explain the behaviour of the load network.

Owen