The thermo emf of a thermocouple varies with the temperature $$\theta $$ of the hot junction as $$E = a\theta + b{\theta ^2}$$ in volts where the ratio $$\frac{a}{b}$$ is $${700^ \circ }C.$$ If the cold junction is kept at $${0^ \circ }C,$$ then the neutral temperature is
A.
$${1400^ \circ }C$$
B.
$${350^ \circ }C$$
C.
$${700^ \circ }C$$
D.
No neutral temperature is possible for this termocouple.
Answer :
No neutral temperature is possible for this termocouple.
Solution :
Neutral temperature is the temperature of a hot junction at which $$E$$ is maximum.
$$ \Rightarrow \frac{{dE}}{{d\theta }} = 0\,{\text{or}}\,a + 2b\theta = 0 \Rightarrow \theta = \frac{{ - a}}{{2b}} = - 350$$
Neutral temperature can never be negative hence no $$\theta $$ is possible.
Releted MCQ Question on Electrostatics and Magnetism >> Electric Current
Releted Question 1
The temperature coefficient of resistance of a wire is 0.00125 per $$^ \circ C$$ At $$300\,K,$$ its resistance is $$1\,ohm.$$ This resistance of the wire will be $$2\,ohm$$ at.
The electrostatic field due to a point charge depends on the distance $$r$$ as $$\frac{1}{{{r^2}}}.$$ Indicate which of the following quantities shows same dependence on $$r.$$
A.
Intensity of light from a point source.
B.
Electrostatic potential due to a point charge.
C.
Electrostatic potential at a distance r from the centre of a charged metallic sphere. Given $$r$$ < radius of the sphere.