Question

The thermo e.m.f. E in volts of a certain themocouple is found to vary with temperature T of hot junction while cold junction is kept at $0^{o}C$, as $E=40T-\frac{T^2}{20}$.
The neutral temperature of the couple is

• A. ${100}^{o}C$
• B. ${200}^{o}C$
• C. ${400}^{o}C$
• D. ${800}^{o}C$

Answer 1

Answer: (C)

${400}^{o}C$

Give: $E=40T-\frac{T^2}{20}$
At neutral temperature, $\frac{dE}{dT}=0$
$\Rightarrow 40-\frac{2T}{20}=0$
$\Rightarrow \frac{T}{10}=40$
$\Rightarrow T={400}^{0}C$