GATE 2022 IN – Question 19

Sensors and Industrial Instrumentation · Temperature and analytical sensors · 1 mark · Multiple choice

A Chromel–Alumel thermocouple has junction A at $T_A$. An ideal voltmeter reads thermal emf $E_1$ between open ends B1 and B2, both at $T_B$. Identical copper wires are introduced between B1–C1 and B2–C2 as shown. With C1 and C2 both at $T_C$, the voltmeter reads $E_2$. Then ______.

Diagram for GATE 2022 IN question 19

$E_1<E_2$
$E_1>E_2$
$E_1=2E_2$
$E_1=E_2$

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Correct answer: (D) $E_1=E_2$

Explanation

Both added copper leads span the same endpoint temperatures, so their thermoelectric contributions cancel in the differential measurement. The law of intermediate metals preserves the original emf: **E1=E2, D**.