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Question
Find the thermo-emf developed in a copper-silver thermocouple when the junctions are kept at 0°C and 40°C. Use the data given in the following table.
| Metal with lead (Pb) |
a `mu V"/"^oC` |
b `muV"/("^oC)` |
| Aluminium | -0.47 | 0.003 |
| Bismuth | -43.7 | -0.47 |
| Copper | 2.76 | 0.012 |
| Gold | 2.90 | 0.0093 |
| Iron | 16.6 | -0.030 |
| Nickel | 19.1 | -0.030 |
| Platinum | -1.79 | -0.035 |
| Silver | 2.50 | 0.012 |
| Steel | 10.8 | -0.016 |
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Solution
Difference in temperature, θ = 40°C
Emf, Ecs = acsθ + `1/2` bcsθ2 ...........(1)
acs = [2.76 − (−43.7) μV
= 46.46 μV/°C
bcs = [0.012 − (−0.47) μV/°C
= 0.482 μV/°C2
Putting this value in eq. (1), we get:-
Ecs = 46.46 × 10−6 × 40 + `1/2` × 0.482 × 10−6 × (40)2
= 1.04 × 10−5 V
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