The Seebeck Effect
If a wire of one material is connected by wires of another material to a galvanometer and the two junctions kept at different temperatures a potential difference is set up and a current flows. The magnitude of the potential difference and current depend on the temperature difference and the materials used to form the junctions.
This device is called a thermocouple and the phemonon is known as the Seebeck effect, after Mr. Seebeck in 1821. If the temperature is varied widely, the voltage varies as an inverted parabolic arc.
Eθ = αθ + βθ-2
The maximum value of the voltage ocurs at the neutral temperature while the temperature at which the sign of the voltage changes it is called the inversion temperature.