The thermo emf of a thermocouple varies with the temperature \Theta of the hot junction as E=a\Theta+b\Theta ^{2}   in volt where the ratio a/b is  700°C .  If the cold junction is kept at 0°C, then the neutral temperature is     

  • Option 1)

    700°C

  • Option 2)

    350°C

  • Option 3)

    1400°C

  • Option 4)

    no neutral temperature is possible for this thermocouple.

 

Answers (2)

As we learnt in

E.m.f of cell -

The potential difference accross the terminals of a cell when it is not supplying any current is called e.m.f

-

 

 E=a\Theta +b\Theta ^{2}

\frac{dE}{d\Theta}= a+2b\Theta              \left ( \frac{a}{b}= 100^{\circ}c \right )

At neutral temperature

\frac{dE}{d\Theta } = 0

0=a+2b\Theta _{n}

\Rightarrow \Theta _{n}= \frac{-a}{2b}

\Theta_{n}= \frac{-1}{2}\times \left ( 700 \right )

= -350^{\circ}c

Neutral temperature is calculated to be -350^{\circ}c i.e. no neutral temperature possible this thermocouple.

 


Option 1)

700°C

This option is incorrect.

Option 2)

350°C

This option is incorrect.

Option 3)

1400°C

This option is incorrect.

Option 4)

no neutral temperature is possible for this thermocouple.

This option is correct.

N neha

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