Define Peltier Coefficient.

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Q. Define Peltier Coefficient.

Tamil Nadu DgeTamil Nadu HSC (DGE) Board 2019Subjective· 2mImportance★★★★★

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The Peltier coefficient measures the rate of heat absorbed or released at a thermocouple junction per unit current, and is measured in volts.

When a current flows across the junction of two dissimilar metals in a thermocouple, heat is either absorbed or evolved at that junction (in addition to the usual $I^2R$ Joule heating) -- this reversible thermoelectric effect is called the Peltier effect.

The Peltier coefficient $\pi_{AB}$ of a junction between metals A and B is defined as the amount of heat energy absorbed or liberated at that junction per second, when a current of one ampere flows through the junction. Equivalently, if a current $I$ flowing for time $t$ causes heat $Q$ to be absorbed or evolved at the junction, then: $\pi = \dfrac{Q}{It}$

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2017Set ANNUAL1 markMCQ
$Q. In a given thermocouple, the neutral temperature :$
(a) is a constant
(b) depends on the temperature of cold junction
(c) depends upon the temperature of inversion
(d) both
(b) and (c)
›Reveal solutionSolution

The neutral temperature of a thermocouple is an intrinsic constant of the metal pair, unaffected by the cold-junction temperature; it is the temperature of inversion that shifts with the cold junction.

In a thermocouple, as the hot-junction temperature is raised (with the cold junction held at some fixed reference temperature $T_c$ ), the thermo-EMF first increases, reaches a maximum at a particular hot-junction temperature called the neutral temperature $T_n$ , and then decreases — eventually reversing sign at a still higher temperature called the temperature of inversion $T_i$ .

The neutral temperature $T_n$ is determined entirely by the thermoelectric properties (the Seebeck coefficients as functions of temperature) of the particular pair of metals forming the thermocouple — it is where the thermoelectric power $\dfrac{d\varepsilon}{dT}$ becomes zero, a condition set purely by the materials involved. Experimentally and theoretically, $T_n$ is found to be independent of the cold-junction temperature $T_c$ : however cold or warm the reference (cold) junction is kept, the EMF still peaks at the same hot-junction temperature $T_n$ for a given metal pair. This is why $T_n$ is treated as a constant characteristic of the thermocouple.

By contrast, the temperature of inversion $T_i$ (where the EMF becomes zero and reverses) does depend on the cold-junction temperature, related by the standard relation

$T_n = \frac{T_c + T_i}{2}, \quad \text{i.e.} \quad T_i = 2T_n - T_c.$ …

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Q.Define Peltier Coefficient.

Concept understanding — Thermoelectric Effects (Seebeck, Peltier, Thomson)

Q.Define Peltier Coefficient.

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