When two different conductors or semiconductors, A and B, form a circuit with their ends connected, an electromotive force (EMF) is generated in the circuit as long as the temperatures at the two junctions are different. One end, at temperature T, is called the working end or hot junction, and the other end, at temperature T0, is called the free end (also known as the reference end) or cold junction. The direction and magnitude of this EMF depend on the materials of the conductors and the temperatures at the two junctions.
This phenomenon is called the "thermoelectric effect," the circuit formed by the two conductors is called a "thermocouple," these two conductors are called "thermoelectric elements," and the generated EMF is called the "thermoelectric EMF."
The thermoelectric EMF consists of two parts: one is the contact potential difference between the two conductors, and the other is the temperature difference potential difference within a single conductor.
The magnitude of the thermoelectric EMF in a thermocouple circuit depends only on the materials of the conductors forming the thermocouple and the temperatures at the two junctions, and is independent of the shape and size of the thermocouple. When the materials of the two electrodes of the thermocouple are fixed, the thermoelectric EMF is a function of the temperature difference between the two junctions, t and t0.
