Question

The thermo e.m.f. E in volts of a certain thermocouple is found to vary with temperature difference $\theta$ in ${}^{o}C$ between the two junctions according to the relation
$E=30\theta -\frac{{\theta }^2}{15}$
The neutral temperature for the thermo-couple will be

• A. 450${}^o$C
• B. 400${}^o$C
• C. 225${}^o$C
• D. 30${}^o$C

Answer 1

The correct option is C 225${}^o$C

As given $E=30\theta -\frac{{\theta }^2}{15}$
$\frac{dE}{d\theta }=0$
$\frac{dE}{d\theta }=30-\frac{2\theta }{15}=0$ or $30=2\frac{\theta }{15}$
$\theta =\frac{15\times 30}{2}={225}^{o}C$