Question 37 of 215

The thermo emf E in volt of a certain thermo-couple is found to vary with temperature difference $\mathrm{\theta }$ in $°\mathrm{C}$ between the two junctions according to the relation 

                               $\mathrm{E}=30 \mathrm{\theta }-\frac{{\mathrm{\theta }}^2}{15}$

The neutral temperature for the thermo-couple will be 

(a) $450°\mathrm{C}$                                          (b) $400°\mathrm{C}$

(c) $225°\mathrm{C}$                                           (d) $30°\mathrm{C}$