Question

In a thermocouple, the thermo emf produced is 3 $\mu$V per one degree difference of temperature between two junctions. When the cold junction of such a thermocouple is at ${20}^{0}C$, the thermo emf is 0.3 mV .Then the temperature of the hot junction is:

• A. ${80}^{0}C$
• B. ${100}^{0}C$
• C. ${120}^{0}C$
• D. $100K$

Answer 1

The correct option is C ${120}^{0}C$

Let the temperature difference between two ends be $t^{o}C$. Here emf is $e=at$ where $a=3\times {10}^{-6}V/{}^{o}C$ the emf for temperature difference $t$ is given as $0.3\times {10}^{-3}V=3\times {10}^{-4}V$ So $t=3\times {10}^{-4}/3\times {10}^{-6}={100}^{o}C$.

So temperature of hot end is $20+t=20+100={120}^{o}C$