Hi, a thermocouple is a device that produces an electrical signal when subjected to differing temperatures. It produces an emf and is based on the thermoelectric effect. When two dissimilar metals are joined at the ends, like say a copper wire and an iron wire, it is found that an emf is produced if the two junctions are at different temperatures. The magnitude of the emf depends on the temperature difference.
Part of a theoretical explanation is that electrons in one metal occupy lower energy states than in the other, so some of them flow across the junction. This leaves one metal slightly more positive than the other, and so a contact potential exists between them. If one of the junctions is at a higher temperature, the energy states are altered, there will be a net emf and current will flow.
I hope this helps, Joe.
