Question

Explain why electrons carry a net energy but not a net current in the case of thermal conduction.

Answer 1

Thermal energy is just erratic, jiggling motion. If for instance you have a metallic rod connecting a hot piece of iron to a cold piece of iron. The electrons in the "hot end" of the rod begin moving faster, bumping into and transferring energy to the electrons in the rest of the rod, and then into the cold piece of iron. Each individual electron is still moving erratically though -- there is no coherent movement of the electrons from hot to cold, so there is no current.

Answer 2

sounds like what I put. I said that the movement of electrons while conducting heat move back and forth through the crystal. Also a current needs to have some electromotive force behind it, and a closed circuit.
Thanks!

Answer 3

well hold on... the whole key is that thermal motion is not coherent. If I go into the vacuum of space and throw an electron in some random direction, that constitutes a current even though there's no electromagnetic force behind it and it's not a closed circuit.

But in thermal conduction, there are just as many electrons going left as right, going up as down, and going forward as back. Everything is random, so all the mini currents cancel each other out.

Answer 4

ooh, that makes sense. Even though there is heat being applied to one side of the solid, since it acts like a classical gas the electrons are moving back just as much as forward.

cool, thank you very much