A current flows in a circuit of two dissimilar metals, when the two junctions are kept at different temperatures. The
junction circuit is called thermocouple.
The magnitude and sign of the thermo-emf developed depends on the material of the two metals and the
temperatures of the two junctions. The metals can be arranged in an order called the thermoelectric series such that in a thermocouple made with two metals in the series, the current in the hot junction is from the metal preceding in the series to the one occuring later.
The inverse effect in which heat is evolved or absorbed at the junctions of two dissimilar conductors if a current is
flowing in the circuit is known as Peltier effect.
Pelter effect and Seebeck effect are linked by Thompson effect according to which when a current is passed
through a single wire in which temperature gradient exists, heat exchange with the surround must take plac if the temperature gradient is to be maintained.
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