Question

The value of Peltier coefficient of a thermocouple

• A. does not vary with absolute temperature of the junction
• B. varies with absolute temperature of the junction
• C. does not depend on the two different metals forming the junction
• D. varies with the direction of current

Answer 1

Answer: (A)

does not vary with absolute temperature of the junction

The Peltier Coefficient represents the heat current flowing per unit charge through the material and does not vary with absolute temperature.

Consider two materials joined together with current flowing in a particular direction as shown. Now, the upper junction gets heated acquiring a temperature $T^2$ and lower junctions remains at a lower temperature $T^1$.

The Peltier heat absorbed by the lower junction per unit time Q is given by

$Q^{\prime }=\pi {}_{AB}I=[{\pi }_A-{\pi }_B]AI$

$pi{}_{AB}$ --- Peltier Coefficient of the entire circuit

$pi{}_A$ --- Peltier Coefficient of material A

$pi{}_B$ --- Peltier Coefficient of material B

The heat current shows discontinuity at the junctions because $pi{}_A$ and $pi{}_B$ are different.