Nick Palmer wrote:
Steven - I wasn't trying to insult you or Michel, however I was
definitely trying to insult Paul after his appallingly arrogant
"intelligent thinking beings" crack. Where is the late, great Chris
Tinsley when you need him? He could, and did, squash adolescent
grandstanding like this in a couple of sentences. I am not in his
league. For you Steve and Michel, I will see if I can explain what I
meant because what you said appeared to show that you did not get my
argument.
Firstly, I did not say that there is no THERMAL noise (obviously there
is from the Brownian motion) I said that there is no thermally induced
effective *voltage* noise when there is no current flowing. Consider the
molecular situation in, say, a carbon resistor which is nicely noisy.
The Brownian motion of the carbon atoms clearly creates communicated
vibrations (thermal noise) but no effective electric noise - one could
argue that the electron cloud around the carbon atoms "vibrating"
creates a varying electric field around the atom at very close range but
this is not going to be a useable or rectifiable voltage.
If one argues that there are ionised carbon atoms present and that it is
the free electrons that are influenced you might have an argument that
by using a naturally very ionised substance it may increase the effect
you are looking for. However, the equation is analysed further on in
the web site, clearly written by someone familiar with sound
engineering, and it goes on to state that the thermal noise is
*independent* of the material of the resistor and only depends on the
value of the resistance and the absolute temperature. It follows that a
material with zero free electrons would have exactly the same thermal
noise i.e. purely due to the Brownian motion of the molecules.
Thanks for the additional explanation; in fact, I'm still not sure I
actually "got it". I've tried the experiment of amplifying and
"listening to" a resistor with no current through it in the past, in the
hope of actually seeing a noise signature of some sort, and never found
anything, but there could have been a number of explanations for that,
of course (starting with my use of a noisy opamp).
This is a fascinating subject IMHO but I'm going to have to find some
time to put more thought into it before I can say anything further that
is ... ahem ... "intelligent"...
Steven wrote
<<And I do not believe that the noise jumps from 0 to its "full-on
value" as soon as the current goes from exactly 0 to, say, 1
fempto-pico-amp.
the formula given in an earlier post, with which you did not disagree,
certainly does not describe something which
decreases with current. If it just _cuts_ _off_ at zero current, that
would be very strange behavior indeed! >>
This is where the "sound engineer's" (as opposed to a physicist's)
equation comes in. Yes, I do believe it jumps from zero to its full on
"thermal noise influencing free electrons" value in exactly the same way
as there is no current in a wire until you flick the switch and apply a
voltage.
Well.... the current through the wire, in the sound engineer's world,
goes up linearly with the voltage dropped by the wire. It would be nice
if the sound engineer's formula for noise showed _some_ dependence on
the current or voltage, if the noise isn't also present at zero volts!
I have problems with formulas describing physical situations which are
discontinuous at zero -- it typically means something significant got
left out (as, come to think of it, I think you already said).
When a sound engineer "listens" to a noisy resistor with a "low
noise amp" he is, in a Schrödinger's cat sort of way, measuring a system
but also affecting that system at the same time - the connection of the
amp inputs *will* generate very small currents in the resistor and these
will be influenced by the *thermal* noise and this will be the source of
the amplified "electrical noise" which Paul hopes to rectify and light
his LEDs with prior to powering the entire world with them. He is
expecting to cohere random vibrations losslessly and output cohered
useable energy capable of doing work at the same energy level. THIS WILL
NOT WORK.
Yeah, well, right, no disagreement there, and I don't have a lot to add
on the discussion of "intelligence", either...
- Re: [Vo]: Quantum Thermodynamics Stephen A. Lawrence
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