Question

The termo-emf of a thermocouple is $40\mu V$ per degree temperature difference. A galvanometer of $50\mu \Omega$ resistance capable of detecting current as low as 10A is connected with one such thermocouple. The smallest temperature difference that can be dected by such a thermocouple is

• A. ${17.5}^{o}C$
• B. ${12.5}^{o}C$
• C. ${8.5}^{o}C$
• D. ${2.5}^{o}C$

Answer 1

Answer: (B)

${12.5}^{o}C$

A galvanometer of $50\mu \Omega$ resistance capable of detecting current as low as 10A is connected with one such thermocouple, hence the voltage is
$V=10\times 50=500\mu V$
Required smallest temperature difference that can be detected by such a thermocouple
$T=\frac{500\times {10}^{-6}}{40\times {10}^{-6}}=(12.5{)}^{o}C$