The contact potential difference at the same temperature all the contacts in a closed circuit of metal wires can not create the current, as it only equalizes the flow of electrons in opposite directions. If you find the algebraic sum of all changes in potential of the contacts of such a circuit, it will be equal to zero. Therefore, in these conditions, the contact potential difference is e. d. with. (rice. 18.5). However, if the temperature of the contacts C and D will be different, in the chain of any e. d. with.

Indeed, if heat contact D, it will be a transition of electrons from the metal into the metal And, and the contact potential difference in the connection D will increase. As in the metal And on the end of the D electrons become more, they will rush to the end With. The increase in the concentration of electrons at the end With will cause the transition metal And the metal via In contact With. Here they are on metal In turn to the contact D. Thus, if the temperature of the contact D will be all the time more, than contact With, then a closed circuit will be a directed motion of electrons counterclockwise. Therefore, in such a circuit operates e. d. with. E. d. with. in a closed circuit, composed of dissimilar metals, due to different temperatures of contacts, is called thermoelectric power (thermo-e. d. S.). Thermo-e. d. with. in the circuit of two different metals is directly proportional to the temperature difference between their contacts and depends on the kind of metals. Electrical energy in this circuit is obtained at the expense of the internal energy source, support the temperature difference between the contacts.

Note, the thermo-e. d. with. small and reaches for metals statystycznych shares of only a few volts per degree temperature difference between the contacts in the circuit. The more thermal e. d. with. in semiconductors (she reaches a thousandth of a volt per degree). This is due to the, that the concentration of electrons in semiconductors is strongly dependent on temperature. The device, consisting of two dissimilar metals with soldered ends, which creates electrical energy due to the internal energy of another body, support the temperature difference between the junctions, called a thermocouple or thermocouple. The thermocouple with one junction, soldering wire segments (or plate) of two dissimilar metals, and to. the free ends are attached the external circuit and measuring devices. The role of the second (cold) perform junction contact with the wires of the external circuit.