The thermo $e.m.f.$ of a thermo-couple is $25\,\mu V{/^o}C$ 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 ................ $^oC$
AIEEE 2003, Medium
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$e = iR$
$25 \times {10^{ - 6}} \times \Delta \theta = {10^{ - 5}} \times 40$
$\Delta \theta = \frac{{40 \times {{10}^{ - 5}}}}{{25 \times {{10}^{ - 6}}}} = \frac{{400}}{{25}} = 16\,^oC$
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