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`

Explanation

Let `e=alpha(theta-theta_(c))+beta(theta^(2)-theta_(c)^(2))`
where `theta_(c)=` temperature of cold junction.
at inversion temperature `e=0rArr theta_(i)=- theta_(c).-(alpha)/(beta)`
at neutral temperature `(de)/(d theta)=0`
`rArr theta_(n)=-(alpha)/(2beta)`
`rArr theta_(i)=-(alpha)/(beta)-theta_(c)=2theta_(n)-theta_(c)rArr theta_(n)=(theta_(i)+theta_(c))/(2)`
`rArr300=(620+theta_(c))/(2) rArr theta_(c)=-20^(@)C`