The thermo-electric effect is the direct conversion of the temperature differences to the electrical voltage and vice versa. A thermo-electric device creates voltage when there is a different temperature on each side. On the other hand, when a voltage is applied, it creates a temperature difference. At atomic scale, an applied temperature gradient causes the charge carriers in the material to diffuse from the hot side to the cold side.
This effect can be used to generate electricity, measure temperature or change the temperature of objects. Because the direction of heating and cooling is determined by the polarity of the applied voltage, thermoelectric devices can be used as temperature controllers.
The term "thermo-electric effect" encompasses three separately identified effects: the Seebeck effect, the Peltier effect and the Thomson effect. Textbooks can refer to it as the Peltier-Seebeck effect. This separation derives from the independent discoveries of the French physicist Jean Charles Athanase Peltier and the German Baltic physicist Thomas Johann Seebeck. Joule heating, the heat generated each time a current is passed through a resistive material, is related, although generally not called thermoelectric effect. The Peltier-Seebeck and Thomson effects are thermodynamic-ally reversible, whereas the Joule heating is not.