AP EAMCET · PHYSICS · Thermal Properties of Matter

If the cold junction is held at \(0^{\circ} \mathrm{C}\), the same thermo emf \(V\) of a thermocouple varies as \(V=10 \times 10^{-6} t-\frac{1}{40} \times 10^{-6} t^2\), where \(t\) is the temperature of the hot junction in \({ }^{\circ} \mathrm{C}\). The neutral temperature and the maximum value of thermo emf are respectively :

A \(200^{\circ} \mathrm{C} ; 2 \mathrm{mV}\)
B \(400^{\circ} \mathrm{C} ; 2 \mathrm{mV}\)
C \(100^{\circ} \mathrm{C} ; 1 \mathrm{mV}\)
D \(200^{\circ} \mathrm{C} ; 1 \mathrm{mV}\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(200^{\circ} \mathrm{C} ; 1 \mathrm{mV}\)

Step-by-step Solution

Detailed explanation

Given, \(V=10 \times 10^{-6} t-\frac{1}{40} \times 10^{-6} t^2\) At neutral temperature \(\frac{d V}{d t}=0\) \(\therefore \quad 10 \times 10^{-6}-\frac{1}{20} \times 10^{-6} t_n=0\) or \(\quad t_n=200^{\circ} \mathrm{C}\) Also at neutral temperature, thermo emf is maximum.…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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