Thermoelectric Thermometers Physical Principles Thermoelectric force It was T. Seebeck who discovered, in 1821, the effect which now bears his name . He observed that a current flows in a closed loop oftwo dissimilar metals when theirjunctions are at two different temperatures. As Ohm's law was not formulated by G. S. Ohm until 1826, the quantitative description of this phenomenon was not possible at the time of its discovery . In 1834, . Peltier, discovered that a junction of two dissimilar metals is respectively heated or cooled when a current is passed through it either in one direction or the other. This phenomenon. | Temperature Measurement Second Edition L. Michalski K. Eckersdorf J. Kucharski J. McGhee Copyright 2001 John Wiley Sons Ltd ISBNs 0-471-86779-9 Hardback 0-470-84613-5 Electronic Thermoelectric Thermometers Physical Principles Thermoelectric force It was T. Seebeck who discovered in 1821 the effect which now bears his name. He observed that a current flows in a closed loop of two dissimilar metals when their junctions are at two different temperatures. As Ohm s law was not formulated by G. S. Ohm until 1826 the quantitative description of this phenomenon was not possible at the time of its discovery. In 1834 . Peltier discovered that a junction of two dissimilar metals is respectively heated or cooled when a current is passed through it either in one direction or the other. This phenomenon is quite distinct from and in addition to the flR Joule heat which is generated by the current flowing in the lead resistance. Another effect distinguishably different from the previous was discovered by Lord Kelvin W. Thomson in 1854. He concluded that a homogeneous current-carrying conductor lying in a temperature gradient will absorb or generate heat in addition to and independently of Joule heating. This absorption or generation of heat depends upon the metal properties and the respective direction of the current. The Peltier and Thomson effects concern only heat generation or absorption but do not generate any thermoelectric forces. Thus they only represent thermal phenomena which accompany the flow of electric current Reed 1992 . In practice the currents flowing in a thermoelectric circuit are so small that the Peltier and Thomson effects can be totally neglected. Of these three thermoelectric effects only the Seebeck effect is the real source of thermoelectric force. This force results from the variation of electron density along a conductor subject to a non-uniform temperature distribution. In this book the thermoelectric force will be called thermal .
