The thermo emf E of a thermocouple is found to vary wit temperature T of the junction (cold junction is `0^(@)C`) as
`E=40T-(T^(2))/(20)`
The temperature of inversion for the thermocouple is

Options

A. `200^(@)C `
B. `400^(@)C`
C. `800^(@)C`
D. `1000^(@)C`

Explanation

The temperature of inversion `T_(i)=2T_(n)-_(c)` whre
`T_(c)=0^(@)C ` and `T_(n)` is netural temperature.
At `T_(n) ,(dE)/(dt)=0`
`therefore E=40T-(T^(2))/(20)rArr(dE)/(dt)=40-(2T)/(20)`
or `0 =40-(2T_(n))/(20)rArr T_(n)=400^(@)C`
`therefore T_(i)=2T_(n)-T_(c)`
`=(2xx400)-0=800^(@)C`