Q67 / 120 · NEET 2011 (Mains) · Physics
A thermocouple of negligible resistance produces an emf of $40 \mu \mathrm{V} /{ }^{\circ} \mathrm{C}$ in the linear range of temperature. A galvanometer of resistance $10 \Omega$ whose sensitivity is $1 \mu \mathrm{A} /$ div, is employed with the termocouple. The smallest value of temperature difference that can be detected by the system will be
- A$0.5^{\circ} \mathrm{C}$
- B$1^{\circ} \mathrm{C}$
- C$0.1^{\circ} \mathrm{C}$
- Correct answerD$0.25^{\circ} \mathrm{C}$
Solution
For minimum deflection of 1 division require current $=1 \mu \mathrm{A}$
voltage required $=i R=1 \times 10=10 \mu \mathrm{V}$
$$
\begin{aligned}
\therefore \quad 40 \mu \mathrm{V} & \cong 1^{\circ} \mathrm{C} \\
10 \mu \mathrm{V} & \cong \frac{1}{4}{ }^{\circ} \mathrm{C} \\
& =0.25^{\circ} \mathrm{C}
\end{aligned}
$$
Hence, the correct answer is option: 'D'.