JEE MAIN - Physics (2004 - No. 21)
The thermo $$emf$$ of a thermocouple varies with temperature $$\theta $$ of the hot junction as $$E = a\theta + b{\theta ^2}$$ 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
$${1400^ \circ }C$$
$${350^ \circ }C$$
$${700^ \circ }C$$
No neutral temperature is possible for this termocouple.
Explanation
Neutral temperature is the temperature of a hot junction at which $$E$$ is maximum.
$$ \Rightarrow {{dE} \over {d\theta }} = 0$$
or $$a + 2b\theta = 0 \Rightarrow \theta = {{ - a} \over {2b}} = - 350$$
Neutral temperature can never be negative hence no $$\theta $$ is possible.
$$ \Rightarrow {{dE} \over {d\theta }} = 0$$
or $$a + 2b\theta = 0 \Rightarrow \theta = {{ - a} \over {2b}} = - 350$$
Neutral temperature can never be negative hence no $$\theta $$ is possible.
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