Thomson effect

The Thomson effect is one of the thermoelectric phenomena , which consists in the fact that in a uniformly uniformly heated conductor with direct current , in addition to the heat released in accordance with the Joule-Lenz law, additional Thomson heat will be released or absorbed in the volume of the conductor depending on the direction of the current .

The amount of Thomson heat is proportional to the strength of the current , time and temperature difference, depending on the direction of the current.

The effect was discovered by William Thomson in 1851 .

The explanation of the effect in the first approximation is as follows. Under conditions where a temperature gradient exists along the conductor through which the current flows, and the current direction corresponds to the movement of electrons from the hot end to the cold, when moving from a hotter to a colder section, the electrons transfer excess energy to surrounding atoms (heat is released), and in the opposite direction of the current, passing from the colder section to the hotter, replenish their energy due to surrounding atoms (heat is absorbed).

In semiconductors, it is important that the concentration of carriers in them strongly depends on temperature. If the semiconductor is heated unevenly, the concentration of charge carriers in it will be greater where the temperature is higher, so the temperature gradient leads to a concentration gradient, as a result of which a diffusion flow of charge carriers occurs. This leads to a violation of electroneutrality. The separation of charges generates an electric field that prevents separation. Thus, if the semiconductor has a temperature gradient, then it has a volume electric field $E^{'}$ ${\ displaystyle E '}$ $E '$ .

Suppose now that an electric current is passed through such a sample under the influence of an external electric field $E$ ${\ displaystyle E}$ $E$ . If the current goes against the internal field $E^{'}$ ${\ displaystyle E '}$ $E '$ , then the external field must do additional work when moving charges relative to the field $E^{'}$ ${\ displaystyle E '}$ $E '$ , which will lead to the release of heat, additional to the Lenz-Joule losses. If current (or external field $E$ ${\ displaystyle E}$ $E$ ) sent by $E^{'}$ ${\ displaystyle E '}$ $E '$ then $E^{'}$ ${\ displaystyle E '}$ $E '$ It itself does the work of moving charges to create current. In this case, the external source spends energy to maintain the current less than in the case when the internal field $E^{'}$ ${\ displaystyle E '}$ $E '$ not. Field work $E^{'}$ ${\ displaystyle E '}$ $E '$ can be made only due to the thermal energy of the conductor itself, so it is cooled. The phenomenon of heat generation or absorption in a conductor due to a temperature gradient during the passage of current is called the Thomson effect. In this way, the substance heats up when the fields $E$ ${\ displaystyle E}$ $E$ and $E^{'}$ ${\ displaystyle E '}$ $E '$ oppositely directed, and cools when their directions coincide.

In the General case, the amount of heat released in the volume dV is determined by the ratio:

dQ^{T}=-\tau (\nabla T\cdot \mathbf {j} )dtdV

{\ displaystyle dQ ^ {T} = - \ tau (\ nabla T \ cdot \ mathbf {j}) dtdV}

{\ displaystyle dQ ^ {T} = - \ tau (\ nabla T \ cdot \ mathbf {j}) dtdV}

where

\tau

{\ displaystyle \ tau}

\ tau

- Thomson coefficient.

Thomson effect

See also

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