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

Correct answer: D. no neutral temperature is possible for this thermocouple E=a θ+b θ^2 so (d E)/(d θ)=a+2 b θ For neutral temperature θ=θ_ n , dE d θ =0 or a+2 b θ_n=0 or θ_ n =-a / 2 ~b=-700 / 2=-350^ C As cold junction is at 0^ C so negative neutral temperature can not be possible.

JIPMER 2012

Exam: JIPMER
Year: 2012
Subject: Physics
Chapter: Electromagnetic Induction

JIPMER 2012 · Physics · Electromagnetic Induction

The thermo emf of a hypothetical thermocouple varies with the...

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

\frac{a}{b}

700^{\circ} \mathrm{C}

. If the cold junction is kept at

0^{\circ} \mathrm{C}

, then the neutral temperature is

Options

A $700^{\circ} \mathrm{C}$
B $1400^{\circ} \mathrm{C}$
C $390^{\circ} \mathrm{C}$
Dno neutral temperature is possible for this thermocouple

Correct answer

D. no neutral temperature is possible for this thermocouple

Step-by-step solution

E=a \theta+b \theta^2

\frac{d E}{d \theta}=a+2 b \theta

For neutral temperature

\theta=\theta_{\mathrm{n}}, \frac{\mathrm{dE}}{\mathrm{d} \theta}=0

a+2 b \theta_n=0

\theta_{\mathrm{n}}=-\mathrm{a} / 2 \mathrm{~b}=-700 / 2=-350^{\circ} \mathrm{C}

As cold junction is at

0^{\circ} \mathrm{C}

so negative neutral temperature can not be possible.

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