Question

Match the following , regarding the terms used in thermo-emf where, T is the temperature difference between the hot and cold junction and a and b are the parameters of the material used

a) Neutral temperature	e) - a/b
b) Temperature of inversion	f) - a/2b
c) Maximum thermo emf	g) $a^2$/4b
d) Thermo electric power	h) a+bT

• A. a - f ,b- e, c- h, d -g
• B. a - f ,b - e, c - g, d - h
• C. a- f ,b- g, c - e, d - h
• D. a -e,b- f ,c - g, d- h

Answer 1

The correct option is B a - f ,b - e, c - g, d - h

Thermo-emf generated is given by $E=a\theta +\frac{1}{2}b{\theta }^2$ where $\theta$ is temperature diference.

$\frac{dE}{d\theta }=a+b\theta$

The emf is maximum when $\frac{dE}{d\theta }=0$ or $\theta =\frac{-a}{b}$ . This is the neutral temperature.

And, the maximum emf is $E_{max}=a\left(\frac{-a}{b}\right)+\frac{1}{2}b{\left(\frac{-a}{b}\right)}^2=\frac{-a^2}{2b}$

The emf becomes zero(0) at $\theta =\frac{-2a}{b}.$This is the inversion temperature.

Thermoelectric power is given by $\frac{dE}{d\theta }=a+b\theta$