Question

The figure shows a Chromel-Alumel thermocouple, where the junction A is held at temperature \( T_A \), and a thermal emf \( E_1 \) is measured using an ideal voltmeter between the open ends B1 and B2, both held at temperature \( T_B \). Two identical copper wires are introduced between B1-C1 and B2-C2 as shown in the figure. When C1 and C2 are held at temperature \( T_C \), the voltmeter reads a thermal emf \( E_2 \). Then, _________

• A. ( E_1&t;E_2 \)
• B. ( E_1>E_2 \)
• C. ( E_1 = 2E_2 \)
• D. ( E_1 = E_2 \)

Hint:

In thermocouples, when additional conductors are added, as long as they are at the same temperature, the overall emf readings remain the same.

Answer 1

The Correct Option is D

Step 1: Understanding the Thermocouple Principle.
In the figure, we have a Chromel-Alumel thermocouple where the thermal emf \( E_1 \) is measured between two points (B1 and B2) at the same temperature \( T_B \). The thermal emf is related to the temperature difference between the junctions. Step 2: Behavior when C1 and C2 are Introduced.
When the identical copper wires (C1 and C2) are introduced between B1-C1 and B2-C2, and the junctions C1 and C2 are held at temperature \( T_C \), the voltmeter will read a thermal emf \( E_2 \). The presence of C1 and C2 at temperature \( T_C \) does not change the overall measurement, as the system remains at thermal equilibrium. Step 3: Conclusion.
Thus, \( E_1 \) and \( E_2 \) are both governed by the same temperature difference between the junctions, meaning \( E_1 = E_2 \).