The thermo e.m.f. of a thermo-couple is $25 \mu \mathrm{V} /{ }^{\circ} \mathrm{C}$ at room temperature. A…

The thermo e.m.f. of a thermo-couple is $25 \mu \mathrm{V} /{ }^{\circ} \mathrm{C}$ at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as $10^{-5} \mathrm{~A}$, is connected with the thermo couple. The smallest temperature difference that can be detected by this sytem is
  1. $16^{\circ} \mathrm{C}$
  2. $12^{\circ} \mathrm{C}$
  3. $8^0 \mathrm{C}$
  4. $20^{\circ} \mathrm{C}$

Solution

$\Delta \mathrm{T}=\frac{40}{25 \times 10^{-6} \times 10^{-5}} \Rightarrow \Delta \mathrm{T}=16^0 \mathrm{C}$

Asked in: JEE Main 2003

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