A thermocouple of negligible resistance produces an $e.m.f.$ of $40\,\mu V{/^o}C$ in the linear range of temperature. A galvanometer of resistance $10\; ohm$ whose sensitivity is $1\;\mu A/div$, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be
AIPMT 2011, Medium
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(d) For minimum deflection of 1 divison require current $=1 \mu A$
Voltage required $=i R=1 \times 10=10 \mu V$
$\therefore 40 \mu V \cong 1^{\circ} C$
$10 \mu V \cong \frac{1}{(4)^{\circ}} C$
$=2.50^{\circ} C$
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