Q. When the temperature difference between hot and cold junctions of a thermo-couple is 100 K an emf of 1 V is generated. Assume the cold junction is heated by 20 K, the percentage change in thermo emf is
A) 20%
B) 30%
C) 40%
D) 25%
Explanation
(a) Assume thermo emf $E$ is directly proportional to temperature difference $T$.
$ie,\ E = aT$
$a = \frac{1}{100} = 10^{- 2}VK^{- 1}$
When cold junction is heated by 20 K, the temperature
difference $T$ between junction becomes 80K, then thermo
emf
$\ E = aT = 10^{- 2} \times 80 = 0.8$ V
Percentage change of emf
$= \frac{E - E'}{E} \times 100$
$\ = \frac{1 - 0.8}{1} \times 100 = 20\%$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.