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peteshimmon
2018-Oct-14, 09:08 AM
Any solid state physicists around? I have been wondering about metals and electricity. I know the atoms have one or two electrons in an outer shell that can be moved by a moving magnetic field. But are they wondering from atom to atom by thermal agitation to a small extent? This means zillions of small electric currents in a block of metal supposedly. Crazy thoughts about two cones back to back causing a herding of some currents to the points maxwell demon style. Then bending the cones around so the points are almost touching. Will a very high frequency very small voltage exist which warms a short conductor between them? Or would you suggest an ice pack for my head? I will not be offended:)

profloater
2018-Oct-19, 04:50 PM
I don't know but I have seen diffusion bonding. You take two highly polished metal pieces and press them together under vacuum to exclude oxygen mainly, and wait. They will bond so well that upon section you cannot see the join. That must be using electrons and shows our normal experience with metals is caused by surface oxides and roughness.

peteshimmon
2018-Oct-19, 05:13 PM
Nice to know someone thinks about these things:) I went to wiki and found silver is better than gold as a coinductor. I was confusing chemical reactivity with conduction. It was Brownian motion I was thinking of when wondering if the electrons move about a lot through thermal activity.

grapes
2018-Oct-19, 06:27 PM
Nice to know someone thinks about these things:) I went to wiki and found silver is better than gold as a coinductor. I was confusing chemical reactivity with conduction. It was Brownian motion I was thinking of when wondering if the electrons move about a lot through thermal activity.
Brownian motion is usually molecules, not electrons.

And, you know that herding by maxwell demons is a thought experiment, right? not really real?

billslugg
2018-Oct-25, 11:46 PM
In a good conductor the conduction electrons form a sort of gas. They have motion depending on their temperature, very similar to Brownian motion. Any mechanism to sort out the more energetic ones would use more energy than it produced.

peteshimmon
2018-Oct-26, 08:58 AM
Refining my thinking I wonder if a short metal rod that is hot might be radiating radio wise due to hordes of electrons randomly moving up an down. And has this been investigated in some type of "anechoic chamber" with radio absorbent stuff to exclude extaneous noise. Also we know that all warm materials give infra red waves presumably due to agitation of whole atoms in the surface. This lower frequency radio emission would just be a small extra loss of energy from conducting material.

profloater
2018-Oct-26, 12:42 PM
It was that radiation of EM that got Einstein interested in the quantised energy idea, of course you mention both infra red and radio , both different frequency bands that we allocate to EM and form a spectrum for all warm and hot objects. Then for conductors we know specific lengths have resonance with radio waves, not related to thermoelectric radiation but to the movement of electrons in the conductor as used in antennae. So a short metal rod can be radiating in infra red and oscillating at a radio frequency quite separately. Except that conductivity is also temperature dependent and a metal can be defined as a material with a positive temp coeff of resistance.

Grey
2018-Oct-26, 04:09 PM
Refining my thinking I wonder if a short metal rod that is hot might be radiating radio wise due to hordes of electrons randomly moving up an down.I think that with the electrons just moving randomly, there's no net change in the charge distribution, and so there won't be the kind of radio emission that you'd see in an antenna that's being driven. That said, of course radio waves are part of a blackbody spectrum just like all other electromagnetic radiation. Any hot object will be emitting radio waves, and the intensity will increase as the temperature goes up.

chornedsnorkack
2018-Oct-27, 05:32 PM
That said, of course radio waves are part of a blackbody spectrum just like all other electromagnetic radiation. Any hot object will be emitting radio waves, and the intensity will increase as the temperature goes up.

Only if the hot object has ability to emit and absorb radio waves. All black bodies have Rayleigh tail all the way to radio waves, but not all hot bodies are black. A white body, that either reflects the incident radiation or passes them through, is also unable of emitting them.

Geo Kaplan
2018-Oct-27, 06:23 PM
Any solid state physicists around? I have been wondering about metals and electricity. I know the atoms have one or two electrons in an outer shell that can be moved by a moving magnetic field. But are they wondering from atom to atom by thermal agitation to a small extent? This means zillions of small electric currents in a block of metal supposedly. Crazy thoughts about two cones back to back causing a herding of some currents to the points maxwell demon style. Then bending the cones around so the points are almost touching. Will a very high frequency very small voltage exist which warms a short conductor between them? Or would you suggest an ice pack for my head? I will not be offended:)

Your intuition is basically right. Brownian motion applies to conduction electrons in metals, much as it applies to atoms and molecules. Thanks to this thermally-driven agitation, there are absolutely instantaneous noise currents and, thanks to Ohm's law, instantaneous noise voltages. However, in thermal equilibrium, there won't be any net transfer of energy, so you can't use a resistor to power your refrigerator. That is, the noise voltage has a zero mean, but a nonzero variance.

To a good approximation, the power spectral density of this noise is constant up to near-optical frequencies (at room temperature). Penzias and Wilson computed carefully how much noise their microwave amplifiers should exhibit, but kept on measuring a stubborn excess. They diligently searched for electronic sources of the discrepancy and found none. And thus the CMB was discovered.