Seebeck Effect a bit of a puzzler

[Arkasha]

Hello all,
I was recently talking about the Seebeck effect with one of my colleagues, and we've run into a bit of a puzzle.
Why are *dissimilar* metals required to produce it? All of the various sources I've consulted state very clearly there must be two different metals (or I suppose you could cheat a bit and use a semiconductor, like Pasco does in its little toys), but none of the sources explained why!
I would have thought that the electron diffusion from the hot to the cold side of each part would create the greatest potential difference if the same metal was used for each "leg."
Clearly there must be something wrong with my thinking . . .
Enlightenment received with gratitude!

 

[FredGarvin]

The Seebeck effect can be produced in a single material. Dissimilar metals are not required to create a voltage potential amongst a single piece.

Take a look at the following link. The answer you need is the first paragraph of section 3 (thermocouples).

http://kasap3.usask.ca/samples/Thermoelectric-Seebeck.pdf

 

[ananthu]

Hello all,
I was recently talking about the Seebeck effect with one of my colleagues, and we've run into a bit of a puzzle.
Why are *dissimilar* metals required to produce it? All of the various sources I've consulted state very clearly there must be two different metals (or I suppose you could cheat a bit and use a semiconductor, like Pasco does in its little toys), but none of the sources explained why!
I would have thought that the electron diffusion from the hot to the cold side of each part would create the greatest potential difference if the same metal was used for each "leg."
Clearly there must be something wrong with my thinking . . .
Enlightenment received with gratitude!

Obviously it is because only different metals, because of their different atomic numbers, have different electron density, producing electron diffusion at the juntiions.
This results in what is called contact potential difference. For two gases to diffuse from one to the other. they must have different pressure. The picture is similar to an electrochemical cell where current is produced only two dissimilar metals are used.