Question

A thermocouple of negligible resistance produces an e.m.f. of $40\mu V{/}^{o}C$ in the linear range of temperature. A galvanometer of resistance 10 ohm whose sensitivity is $1\mu$A/division, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be

• A. ${0.25}^{o}C$
• B. ${0.5}^{o}C$
• C. $1^{o}C$
• D. ${0.1}^{o}C$

Answer 1

The correct option is A ${0.25}^{o}C$

For minimum deflection of 1 division required current $=1\mu A$
$\Rightarrow$ Voltage required $=IR=\left(1\mu A\right)\left(10\right)=10\mu V$
$\therefore 40\mu V\equiv 1^{o}C$
$\Rightarrow 10\mu V\equiv {\frac{1}{4}}^{o}C={0.25}^{o}C$