The thermo e.m.f. of a thermo­couple is 25\, \mu V/^{\circ}C at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as 10-5 A, is connected with the thermocouple. The smallest temperature difference that can be detected by this system is

  • Option 1)

    16^{\circ}C

  • Option 2)

    12^{\circ}C

  • Option 3)

    8^{\circ}C

  • Option 4)

    20^{\circ}C

 

Answers (2)

As we learnt in

Galvanometer -

It is an instrument used to detect small current passing through it by showing deflection.

- wherein

i.e. moving coil galvanometer

moving magnet galvanometer

 

 Let the smallest be \Theta ^{\circ}c

\therefore thermo emf = \left ( 25\times 10^{-6} \right ) \Theta volt

Potential difference acrons galvanometer

= IR= 10^{-5} \times 40

= 4 \times 10^{-4} volt

\therefore \left ( 25\times 10^{-6} \right ) \Theta = 4\times 10^{-4}

\therefore \Theta = \frac{4\times 10^{-4}}{25\times 10^{-6}} = 16^{\circ}c

 

 

 


Option 1)

16^{\circ}C

This option is correct.

Option 2)

12^{\circ}C

This option is incorrect.

Option 3)

8^{\circ}C

This option is incorrect.

Option 4)

20^{\circ}C

This option is incorrect.

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