Question

A thermocouple of negligible resistance produces an e.m.f. of $40\, \mu V/^{\circ}C$ in the linear range of temperature. A galvanometer of resistance $10$ ohm whose sensitivity is $1 \, \mu A/division$, is employed with the thermocouple. The smallest value of temperature difference that can be detected by the system will be

• A. $0.25 ^{\circ} C$
• B. $0.5 ^{\circ} C$
• C. $1^{\circ} C$
• D. $0.1^{\circ} C$

Answer 1

Answer: (A)

$0.25 ^{\circ} C$

Answer 2

For minimum deflection of $1$ division required current $=1 \,\mu A$
$\Rightarrow$ Voltage required $= IR =(1 \,\mu A )(10)=10 \,\mu\, V$
$\therefore 40\, \mu \,V \equiv 1^{\circ} C$
$\Rightarrow 10 \,\mu \,V \equiv \frac{1}{4}{ }^{\circ} C =0.25^{\circ} C$