Yes, this is true, because (explanation that is probably over your head) the mean free path of phonons is shorter in alloys, in which there is more disorder. Roughly, the mean free path of electrons is about the same as that of phonons, so the electrical conductivity is also lower. This is the explanation for the http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html" .Pengwuino said:
A qualitative experiment is easy. You can compare thermal conductivities of different rods with the same diameter by holding them in a candle flame. See for how long you can hold copper, aluminium, iron, brass, and steel.
Quite handy for those of us who like to solder.Integral said:
Sorry,while this is true, it is not the explanation for thermal conductivity, which in metals is by electrons.Pieter Kuiper said:
Yes that Hyperphysics article does talk about Wiedeman-Franz and thermal conductivity. That is not what I had a problem with. However, you said that :erickalle said:
I don't see where that article says anything like this. In fact, I'm pretty sure this isn't stated anywhere on the site. If you got it from a particular page, show a link to that page. I'm pretty sure you just misunderstood something it said in one of its articles on heat capacity or some such.
It would be fair to say that, ONLY if you can actually quote a page on that site that says exactly what you said. In my opinion, the Hyperphysics site is a very high quality physics resource, and I would not expect it to have any gross errors. If it says something that I disagree with, I'd go back and recheck my understanding. While the Drude (classical) result is conceptually flawed, it ends up being very close to the correct result because of two offsetting errors : the heat capacity should be reduced by about 3 orders of magnitude (because of the effect described above), but the mean square thermal velocity (or mean KE) sould be raised by the same order.
Can't disagree with that. Clearly, at a simplistic level, raising the temperature raises the mean velocity of the conduction electrons, and hence will raise the rate of electronic heat transfer.
I believe spell-check has not yet been restored since the upgrade.
Gokul43201 said:
What does (the last part of) this sentence mean ?erickalle said:
2
Does anybody know anything about electrons propagating sound in metals?
That is definitely wrong.
Eric, why do you think we need to change the laws of physics? Please explain more fully.erickalle said:
I am not sure why one would think that the laws of physics must be changed. What contradiction does one perceive?erickalle said:
from http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thercond.html
I can testify this these statements. I have been in situations where I have had to approximate (guesstimate!) thermophysical properties because they simply did not exist - no one had bothered to measure them, especially at high temperature because we simply have not used certain alloys under those conditions.
mezarashi said:
But that is not losing energy, that simply has to do with resistance to movement, and sound is movement of atoms - related to elastic displacement from equilibrium.
At some point yes, as electrons are affected by atomic motion. Perhaps it is more accurate to say that electrical and thermal resistance are explained in terms of phonon scattering.
It's not very clear why you think there is a need for theory revision. Where does the theory not explain the experiment ? Are you suggesting that as temperature is increased, since the KE of the atoms must increase, this will be manifested in an increase in the speed of sound ?erickalle said:
Gokul this answer could finally solve my headache. As I understand it, this is indeed the case for gasses. An increase in temperature will increase KE and therefore the speed of sound in a gas will go up. Please correct me if this is wrong.
The KE of the gas molecules affects the pressure, not the speed of sound.
Astronuc said:
For an ideal gas: KE=1/2mv^2=3/2kT.
This is not wrong.erickalle said:
That's right.
Not exactly, but the relationship is not straightforward. Besides, you've assumed that increasing temperature proportionately increases the KE of the atoms. While this is not an entirely unreasonable line of thinking (it is flawed however, and I may get to that later), you've probably forgotten that a large chunk of the heat can go into the KE of the free electrons, which do nothing for the propagation of sound. Additionally you've applied the same theory to a metal, as you have to an ideal gas. Unfortunately that is not a valid extension. An ideal gas is a non-dispersive medium, while a metal is not.
The theory (beyond the simplistic picture painted above) is hardly trivial. It often takes up a few weeks in an upper undergraduate/graduate level solid state physics course, and even there is hardly ever covered satisfactorily.
Gokul43201 said:
Gokul as you can see from your own statement the heat capacity of electrons is only ~1% of the total.
In general this is true for most metal, but not necessarily for all of them. Nevertheless, notice that this was not what I suggested was the primary reason. I admit, you are justified in neglecting the electronic component of the heat capacity, but that still doesn't solve the problem.erickalle said:
It isn't missing at all - just not easy to get at and digest over a single sitting.
There is also a very carefully laid out theory in general - not just for specific applications. I'd recommend you find Ashcroft & Mermin (or Marder) from a nearby library, if you really want to spend some time on this.
Sheersh (hic) !
Astronuc said:
Astronuc said:
