Determine Thermo-EMF #8211; (a) The potential difference across R must be equal to the emf of standard cell, i.e. IR = E<sub>0</sub> ∴ I = E<sub>0</sub>/R, (b) The small thermo-emf produced in the thermocouple e = xl (d) x = Iρ = IRl/L (c) The value of thermocouple for ordinary temperature difference is very low (10<sup>-6</sup> V). For this, the potential gradient x must be also very low (10<sup>-4</sup> V/m). Hence, a high resistance (R) is connected in series with the potentiometer wire in order to reduce current,