Question

An emf of 0.09V is generated when the temperature difference between the junctions of a thermocouple is 75 K. If the cold junction temperature increases by 15 K, the percentage change in emf is

• A. 15 %
• B. 20 %
• C. 80 %
• D. 40 %

Answer 1

Answer: (B)

20 %

The emf is given as $e=at$, where $t$ is the temperature difference.

At $t=75K,e=0.09V\Rightarrow a=e/t=1.2\times {10}^{-3}V/K$

If the cold junction temperature increases by $15K$, the temperature difference decreases by $15K$ so new $t=75-15=60K$.

Now new emf is $1.2\times {10}^{-3}\times 60=0.072V$

So percentage decrease is $(0.09-0.072)\times 100/0.09=20\%$