Question

The thermo emf of a thermocouple varies with the temperature $?$ of the hot junction as $E = a \,? + b?^2$ 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. $350^{\circ}C$
• C. $1400^{\circ}C$
• D. no neutral temperature is possible for this thermocouple.

Answer 1

Answer: (D)

no neutral temperature is possible for this thermocouple.

Answer 2

$E = a? + b?^2$ At neutral temperature $dE/d? = 0$ $\therefore \frac{dE}{d\theta} = a +2b\theta_{n} = 0 \,;\,\theta_{n}= -\frac{a}{2b}$ Now $\frac{a}{b} = 700^{\circ}C$ (given) $\theta_{n} =-700/2 = -350^{\circ}C$ Now $?_{c} = 0^{\circ}C$. So, $?_{n} > 0^{\circ}C$ But mathematically $?_{n} < 0^{\circ }C.$