Effect description
Seebeck effect consists in the fact that the thermal EMF occurs in the closed loop formed by different conductors if different temperatures are applied in the junctions. A circuit consisting of two different conductors only is called a thermal element or thermocouple.
The value of the occurring thermal EMF, for a first approximation, depends on the material of conductors and temperatures of the hot (Τ1) and cold (Τ2) contacts only.
In a small range of temperatures the thermal EMF (E) can be assumed as proportionate difference of temperatures:
E= α12 (T2- T1 ),
where α 12 - is a thermoelectric ability of the pair (of the coefficient of thermal EMF).
In the simplest case, the coefficient of thermal EMF is determined by materials of conductors only, however, in the strict sense, it depends on the temperature too, and in some cases, with the temperature change, α12 changes the sign.
More correct formula for thermal EMF:
The history of Seebeck effect discovery
In 1823, Fourier and Oersted proved that the thermoelectric effect had the superposition property, and built the first thermoelectric battery consisting of three antimony plates alternated by three bismuth plates and soldered at the ends in a form of hexagon.
Further improvement was introduced in one year by Melloni who designed a prismatic model used to date. On the basis of Melloni battery and the galvanometer of his own construction, Nobili constructed a thermal multiplier in the same 1830 of such sensitivity that it responded to the human body heat at the distance of 18 – 20 elbows.
Seebeck himself describes one of his multiple experiments as follows. A small piece of bismuth was soldered in both ends to a copper spiral. If one end was heated by a lamp, and another remained cold, then the magnetic needle contained within the spiral turned denoting the flow of current that in the cold junction flew from copper to bismuth.
In 1834, in the course of experimental researches of antimony and bismuth conductivity, Jean Charles Peltier (1785-1845) tried to determine how the temperature changes along a homogeneous or different conductor through which the current flew. In this connection, Peltier studied the temperature in different points of thermoelectric circuit by means of thermocouple connected to the galvanometer. He discovered that in soldered connection points of different metals the temperature changes abruptly, there were even cases of cooling. He could achieve the highest effect with the pair bismuth – antimony. Thus, the electric current can cause the cooling too.
In his other experiments Peltier soldered crosswise two pieces of metal, then, connecting the galvanometer made the thermoelectric current to flow through two subsequently connected ends of the cross and through the galvanometer, and in some time he disconnected the circuit and connected the same galvanometer to another two ends of the cross – and the galvanometer showed the current caused either by heating or cooling of the cross soldered points.
Share this article with your colleagues and friends