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Question:

The thermo e.m.f. E in volts of a certain thermocouple is found to vary with temperature difference θ in °C between the two junctions according to the relation E=30θ−θ²/15. The neutral temperature for the thermo-couple will be 450°C, 400°C, 225°C, 30°C

450oC

225oC

30oC

400oC

Solution:

As given
E=30θ−θ²/15
dE/dθ=0
dE/dθ=30−(2θ/15)=0
or 30=2θ/15
θ=15×30/2=225°C