If two wires of dissimilar metals, say copper and iron, be joined at two ends and if the two junctions be maintained at two different temperatures, one higher than the other, then an electromotive force is set up, which causes a current flow in the Circuit. Two metals arranged in this way to form two junctions are called a thermocouple.
The electromotive force produced due to thermal effects in the junctions is Called thermo-electromotive force. The magnitude of thermo-electromotive force depends on the metals used and the temperature difference between the hot and cold junction.
Seebeck, a German physicist, was the first in 1821 to invent this phenomenon and after his name this known as Seebeck effect.