Question

The thermo emf of a hypothetical thermocouple varies with the temperature $\theta$ of hot junction as $E=a \theta+b \theta^{2}$ in volts, where the ratio $a / b$ is $700^{\circ} C$. If the cold junction is kept at $0^{\circ} C$, then the neutral temperature is

• A. $700^{\circ} C$
• B. $1400^{\circ} C$
• C. $-350^{\circ} C$
• D. no neutral temperature is possible for this thermocouple

Answer 1

Answer: (C)

Given, $E=a \theta+b \theta^{2}$
$\therefore p =\frac{d E}{d \theta}=\frac{d}{d \theta}\left(a \theta+b \theta^{2}\right)$
$=a+2 b \theta$
At $\theta =T_{n}, p=0$
$\Rightarrow T_{n} =-\frac{a}{2 b}=-350^{\circ} C$