Seebeck’s effect: German Physicist Thomas Seebeck discovered that when two metal wires are joined to form a closed circuit and two junctions are kept at different temperatures, a small emf is set up in the circuit and the current begin to flow from the metal of low temperature to the metal of high temperature. This effect is known as Seebeck’s effect. The emf thus developed is called thermo emf and the corresponding current is called thermoelectric current. Seebeck’s effect is also known as thermoelectric effect.
Cause of Seeback’s effect:
We know that different metals have different density. When two metals are brought to contact, the free electrons of the metal tends to diffuse from the metal with high density to the metal with lower density. Due to this diffusion, a potential difference is set up at the junction of two metals and effective emf is generated. The rate of diffusion is directly proportional to the difference in density of two metals.
Thermocouples: When a loop is formed by the pair of metal kept at different temperature for the production of thermoelectricity, then the pair of metal is called thermocouple. The magnitude of emf produced in thermocouple is depends upon the metal pair used for this process.
Thermoelectric series: An arrangement of metals in series according to their conductivity order is called thermoelectric series. The thermoelectric series is given below:
Antimony, iron, zinc silver, lead, copper, platinum, cobalt, bismuth
The emf developed will be more if there is larger separation between the chosen metals from thermoelectric series. So, antimony-bismuth thermocouple is considered best for the generation of thermoelectricity.