What is the physics behind the functioning of thermocouples?

[krackers]

Hello there! I am planning to do an experiment on thermocouples but have a few questions.

1. What is the physics behind why the thermocouple works?

2. Why do two different metals need to be used for making this?

Thank you!

 

[K^2]

Do you understand what a Fermi surface is?

 

[krackers]

No, I do not.

However, I did look through wikipedia and I think I might have found a section that pertains to my question. [http://en.wikipedia.org/wiki/Thermoelectric_effect#Charge-carrier_diffusion]

The part I am not clear on is this. [Taken from that article directly]

"If the rate of diffusion of hot and cold carriers in opposite directions is equal, there is no net change in charge. The diffusing charges are scattered by impurities, imperfections, and lattice vibrations or phonons. If the scattering is energy dependent, the hot and cold carriers will diffuse at different rates, creating a higher density of carriers at one end of the material and an electrostatic voltage."

Why would there be no potential difference if the rate of movement of the hot/cool electrons is equal? Why are two different metals necessary? Why would impurities, imperfections, lattice vibrations, or phonons make them diffuse at different rates, and how does that end up creating an electrostatic voltage?