Question

The thermo-emf of a copper-constant couple is $40\mu V$ per degree. The smallest temperature difference that can be detected with this couple and galvanometer of $100\Omega$ resistance capable of measuring the minimum current of $1\mu A$ is

• A. 2.5${}^{o}C$
• B. 2${}^{o}C$
• C. 1.5${}^{o}C$
• D. 1${}^{o}C$

Answer 1

Answer: (A)

2.5${}^{o}C$

Galvanometer of $100\Omega$ resistance capable of measuring the minimum current of $1\mu A$ is $V=100\times {10}^{-6}V$

Required smallest temperature difference that can be detected with thermocouple is $\frac{100\times {10}^{-6}}{40\times {10}^{-6}}={2.5}^{\circ }C$