Laws of Thermo e.m.f.

(i) Law of Intermediate Metals.

 The introduction of any additional metal into any thermoelectric circuit does not alter the thermo emf provided the metal introduced is entirely at the same temperature as the point at which the metal is introduced.

If _aE_b is the emf for a couple made of metals A and B, and _bE_c that for the couple of metals B and C, then the emf for couple of metals A and C is given by

            _aE_c = _aE_b + _bE_c

(ii) Law of Intermediate Temperatures.

The thermo emf E³₁ of a thermocouple whose junctions are maintained at temperatures T₁ and T₃ is equal to the sum of the emfs E²₁ and E³₂ when the junctions are maintained at temperatures T₁ T₂ and T₂, T₃ respectively. Thus

            E³₁ = E²₁ + E³₂


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