The temperature of inversion of a thermocouple is `620^(@)C` and the neutral temperature is `300^(@)C`. What is the temperature of cold junction?

Options

A. `40^(@)C`
B. `20^(@)C`
C. `320^(@)C`
D. `-20^(@)C`

Answer

D

Explanation

Let `e=alpha(theta-theta_(C))+ beta(theta^(2)-theta_(C)^(2))` where ` theta_(C)`= temperature of cold junction at inversion temperature `e=0 implies theta_(i)= - theta_(C) -(alpha)/(beta)` at neutral temperature `(de)/(d theta)=0`
`implies theta_(i)=-(alpha)/(beta)- theta_(C)= 2 theta_(n)- theta_(C) implies theta_(n)=(theta_(i)+ theta_(C))/(2)`
`= 300= (620+ theta_(C))/(2) implies theta_(C) =- 20^(@) C`