Seebeck effect definition
In 1826, Seebeck discovered that an electric current could be produced by thermal means. He found that if a circuit is made of two different metals in series ( say Copper and iron), then on heating one of the junctions, while the other is kept cold, a current is produced in the circuit as shown in the figure. This is called the Seebeck effect or thermoelectric effect.
The pair of different metals by which a thermoelectric current is produced is called a Thermocouple.
The production of electric current due to the temperature difference between two junctions of two dissimilar metals (i.e thermocouple) is called Seebeck or thermoelectric effect.
The flow of current is from copper to iron at a hot junction in Fe-Cu Thermocouple. While the current flows from Antimony to Bismuth through the cold junction in Sb-Bi Thermocouple.
A flow of current in a Thermocouple indicates the existence of an e.m.f and the production of electrical energy. This energy is derived from a gain of heat at the hot junction.
The electromagnetic force produced in this manner i.e by maintaining the junctions of a Thermocouple is called thermoelectric e.m.f and the resulting current is called thermoelectric current.
Origin of Thermo e.m.f.
The density of free electrons in any two different metals at the same temperature is different. When two metals are brought in contact with each other, electrons have a tendency to flow from the metal of higher electron density to the metal of lower electron density. Thus, an electrostatic field and hence if the potential difference is set up between them.
When both the junctions are at the same temperature, the potential difference across one junction is equal and opposite to that across the other junction. Hence no current is produced because the two junctions pump the electrons at the same rate in opposite directions.
When the junctions are at different temperatures, the rate of diffusion of electrons across the two junctions is different and hence the potential difference will be set up across the junction. The junction potential difference so produced in the pair of matter causes a thermo-current to be produced.
4 Applications of Seebeck effect
- The Seebeck effect in thermocouple to measure the temperature difference.
- The Seebeck effect is used in a thermoelectric generator, which functions as a heat engine.
- Used in some power plants to waste heat into additional power.
- In automobiles as automotive thermoelectric generators for increasing fuel efficiency.