Author Topic: Johnson noise thought experiment  (Read 9294 times)

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Zeranin

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Re: Johnson noise thought experiment
« Reply #25 on: May 25, 2016, 07:47:18 am »
As with the guy in the fridge, if you have millions of warm resistors, each with the same noise power, then no matter what we do, we apparently cannot harvest useful electrical noise power either from a single resistor, or any large number of resistors. If we could then the 2nd Law would be broken, but I’m sure that hasn’t stopped many people from trying!

Well why not?  Evidently the guy stuck in the 'fridge is "harvesting useful power".  He could use it to power a conventional heat engine and generate electrical power (at fairly poor efficiency, but decidedly nonzero amount).

Yes you are right, the guy in the fridge can harvest useful power from his resistors because they heat up relative to his environment in the fridge, though this only happens because his resistors and environment are colder than his 'power-station' resistors outside the fridge. He could even run a heat engine from his resistors, just as you say. However, just as with resistors sitting on the bench at room temperature, he apparently can't take the many pairs of wires running into his fridge, and connect them in series or parallel to directly increase the amount of electrical power to run his TV set. Similarly, if you have millions of warm resistors, each with the same noise power, then no matter what we do, we apparently cannot harvest useful electrical noise power either from a single resistor, or any large number of resistors. That's the point I was trying to make, but should have left the fridge guy out of it.

I have always felt that Johnson noise power was such a waste. It causes us untold grief in low-noise designs, and then when we try to harvest it for something useful, it refuses to cooperate.

RIS

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Re: Johnson noise thought experiment
« Reply #26 on: May 25, 2016, 07:57:15 am »
One more question from hell
http://energythic.com/view.php?node=208

Zeranin

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Re: Johnson noise thought experiment
« Reply #27 on: May 25, 2016, 08:28:14 am »
It's a presumed semiconductor implementation of the thought experiment:
https://en.wikipedia.org/wiki/Brownian_ratchet
We like to think that, by some intuition, the ratchet mechanism has zero forward force and infinite reverse force required to turn it; but that's clearly not true, as the pawl is pushed up a ramp as the crank turns, and for the pawl to remain in position, it must be spring-loaded, and this exerts a lever force on the crank.  For thermal motion to be able to turn it, the spring must be so slight that, not only will the crank turn by thermal motion, but the pawl will jitter about as well, allowing the crank to skip backwards after all.  The combined effect is no net movement.

Tim

Beautiful! I especially like the paragraph specifically on attempting to rectify Johnson noise. I'm not surprised that someone (Leon Brillouin) had thought of that idea before, and way back in 1950s. Discussions of this sort are not total nonsense, noting that Brillouin wrote a paper on this in a respected science journal :-

Brillouin, L. (1950). "Can the Rectifier Become a Thermodynamical Demon?". Physical Review 78 (5): 627

The demon, of course, is Maxwell's Demon, a thought experiment by the great scientist James Maxwell. As I have online access to all the science journals, I might even read his paper.

But hey, we can make that diode work OK. We place our rectifier diodes and series/parallel wiring in the fridge, but the 'power-station-warm-resistor-array' at room temperature outside the fridge, and then just have a pair of high-voltage-high-current wires leaving the fridge, connected to our TV, or through an inverter to the power grid or whatever.

Tell you what Tim. Lets split equally on the Nobel Prize. Deal?

T3sl4co1l

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Re: Johnson noise thought experiment
« Reply #28 on: May 25, 2016, 09:09:36 am »
Tell you what Tim. Lets split equally on the Nobel Prize. Deal?

Sure thing!

I'll let you catch the refrigeration bill though.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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John Heath

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Re: Johnson noise thought experiment
« Reply #29 on: May 25, 2016, 10:25:10 am »
If I were stuck on the surface of the sun there could be a problem charging my intergalactic  iPhone to ask for help as there is no energy on the surface of the sun. No energy in that everything is hot therefore no temperature difference to run a heat engine to charge the iPhone. However if a parabolic disk could be constructed pointed away from the sun towards the cold black sky then there would be energy to charge my iPhone from the difference between the sun and cold night sky. The point being made is energy is in entropy or differ4ence not temperature. Johnson noise on a resister is like the temperature on the sun. No energy unless a surface of less Johnson noise can be found to take advantage of the Johnson noise difference between the two.

T3sl4co1l

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Re: Johnson noise thought experiment
« Reply #30 on: May 26, 2016, 12:47:52 am »
Not quite. The corona is much hotter (~MK) than the photosphere (~kK).  A SW antenna will pick up quite a lot of noise, though still not a practical amount, I don't think.

What's peculiar is, 1. how it gets so hot (and I guess that's still not understood), 2. the frequencies where it's hot (mostly at radio frequencies, because there is a high frequency cutoff effect in the corona, just as in the Earth's ionosphere), and 3. the low density and high velocity compared to the photosphere.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!

John Heath

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Re: Johnson noise thought experiment
« Reply #31 on: May 26, 2016, 11:25:00 pm »
Indeed there are more questions than answers when it comes to plasma states. Just a lightening strike will punch its way through our ionosphere to travel alone the Allen belt leading it back on the opposite side of the earth? It can be picked up with VLF receivers when returning as a whistling sound in the audio range , around 5 KHz decreasing to 500 Hz in a 1 to 2 second length. This is thought to be dispersion where high frequencies of a pulse arrive sooner than low frequencies. If so that had to happen in the ionosphere not a magnetic channel of the Allen belt b, I would think. It gets stranger as there is a double hop where it launches itself again returning  through the Allen belt to where it came , lightening strike , with the same odd whistle sound. It seems both electrostatic electricity and plasma states are not the same as electronics. An apple and an orange with different rules.

RandallMcRee

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Re: Johnson noise thought experiment
« Reply #32 on: May 27, 2016, 12:15:28 am »
Is this Spherics?

Quote
The "antenna on the hill" at this year's Stellafane was a simple loop detector for "SPHERICS". Its function is to directly convert very-low-frequency (10 to 10,000 Hz) electromagnetic noise into acoustic sound at the same frequencies. Thus you can hear the otherwise inaudible natural atmospheric noises termed spherics. Some level of noise activity is always present. It was interesting to watch people start to walk by, only to stop in surprise and lean over to hear better, as they realized that the detector was "on" and working.

Amazingly easy to create one of these "telescopes".

https://stellafane.org/tm/tg/avellone02/avellone2.html

John Heath

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Re: Johnson noise thought experiment
« Reply #33 on: May 27, 2016, 04:29:15 am »
Listening to electromagnetic waves in the audio spectrum is over 100 years old and has a few names. Currently the buzz word for this branch of science is VLF for Very Low Frequency reception. And yes they are easy to build. A condenser coupled wire from the mic input of a computer sound card tied to a tree and you are in business. I like to listen in if we have a nice sun burst coming our way. There is great software out there for spectrum analysis of these signals. I can recommend Spectrum lab as the best , freeware as well , by Wolfgang Buescher. He has a web site to chat with him for the finer details.  As this is open software some of the finest minds from around the world have been tweaking it for the last ten years. The end result is one of the nicest spectrum analyzers I have seen.

Smf