Drift of electrons

  • #1

Main Question or Discussion Point

why are good conductors of heat good conductors of electricity as well?
 

Answers and Replies

  • #2
why are good conductors of heat good conductors of electricity as well?
i mean to ask is it something to do with drift of electrons?
also, what factors govern the thermal drift of electrons(if any)
 
  • #3
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what factors govern the thermal drift of electrons(if any)
voltage...potential difference....

yes....heat and electricity conduction are similar:

based on how tightly electrons are bound.....

In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors, such as copper or aluminum, the movable charged particles are electrons (see electrical conduction). Positive charges may also be mobile in the form of atoms in a lattice that are missing electrons (known as holes), or in the form of ions, such as in the electrolyte of a battery. Insulators are non-conducting materials with fewer mobile charges, which resist the flow of electric current.
http://en.wikipedia.org/wiki/Electrical_conductor

Metals (e.g. copper, platinum, gold,etc.) are usually the best conductors of thermal energy. This is due to the way that metals are chemically bonded: metallic bonds (as opposed to covalent or ionic bonds) have free-moving electrons which are able to transfer thermal energy rapidly through the metal. The "electron fluid" of a conductive metallic solid conducts nearly all of the heat flux through the solid. Phonon flux is still present, but carries less than 1% of the energy.
http://en.wikipedia.org/wiki/Conduction_(heat [Broken])
 
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  • #4
K^2
Science Advisor
2,469
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Are you familiar with concept of Fermi-surface? Electrons are fermions, which cannot occupy the same state. That means that all of the states with low kinetic energies are taken, forcing most electrons to occupy energy states with sizable kinetic energies. If temperature is exactly 0, the cutoff is very sharp, and the boundary is called the Fermi-surface.

What's interesting is that if temperature is non-zero, the cutoff is smooth. The higher the temperature, the smoother the cutoff. So if temperature in different parts of material is different, this distorts the Fermi-surface. The distortion is similar to one that happens when you apply voltage, so an electric potential gradient (electric field) and thermal potential gradient are both affecting the movement of electrons in similar ways, relating electric and heat conduction properties.

Of course, a metal also conducts heat via phonons in the metallic lattice. That conduction mode can contribute nearly as much or sometimes more than electrons, and this mode of heat conduction is unrelated to electric properties. So while being a good electric conductor guarantees good heat conductivity, reverse is not always true.
 
  • #5
Are you familiar with concept of Fermi-surface? Electrons are fermions, which cannot occupy the same state. That means that all of the states with low kinetic energies are taken, forcing most electrons to occupy energy states with sizable kinetic energies. If temperature is exactly 0, the cutoff is very sharp, and the boundary is called the Fermi-surface.

What's interesting is that if temperature is non-zero, the cutoff is smooth. The higher the temperature, the smoother the cutoff. So if temperature in different parts of material is different, this distorts the Fermi-surface. The distortion is similar to one that happens when you apply voltage, so an electric potential gradient (electric field) and thermal potential gradient are both affecting the movement of electrons in similar ways, relating electric and heat conduction properties.

Of course, a metal also conducts heat via phonons in the metallic lattice. That conduction mode can contribute nearly as much or sometimes more than electrons, and this mode of heat conduction is unrelated to electric properties. So while being a good electric conductor guarantees good heat conductivity, reverse is not always true.
could u please eleaborate more on fermi surfaces? thanks
 
  • #6
K^2
Science Advisor
2,469
28
Erm... It's a fairly deep subject. I don't think I can cover it in a post. If there is a specific query, I may be able to answer, but if you are looking for general coverage of Fermi Surface, Fermi Energy, etc., you are better off reading up on it elsewhere. By far the best introduction would be from an introductory Solid State text, but it will assume that you have a firm grasp of basic Quantum Mechanics and probably some Statistical Mechanics, at least, as far as understanding Fermi-Dirac distribution. You might be able to get some basic info from Wikipedia article, but I haven't looked at it, so I don't know how detailed or technical it would be.

What's your background in Physics? It might help me point you in the right direction.
 
  • #7
well i am in the last year of my high school
 
  • #8
K^2
Science Advisor
2,469
28
Well, if you had some calculus, there is absolutely nothing there that would be beyond your understanding, but there is a lot of stuff to digest. If you seriously want to understand this, you can try reading Introduction to Quantum Mechanics by David J. Griffiths. It's a good introductory text used in many universities at undergraduate level. In order to move on forward towards free electron gas you need to understand it up to and including particle in a box, aka particle in a square well. Preferably, both infinite and finite potential cases. I think it's one of the first examples of using Shroedinger's Equation, so it should be very near the beginning.

If you haven't had any calculus, you'll need to learn about derivatives. There are some video-lectures on Youtube that cover them in about 10 minutes, though. Not in any sort of detail, but just enough for it not to sound like alien language.
 
  • #9
na, i have done calculus. could u give a link, or a source from where i cud get this book. i surely dont have this in my school library
 

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