The thermo e.m.f. of a thermo -couple is 25 / at room temperature. A galvanometer of 40 ohm resistance, capable of detecting current as low as 10⁻⁵ A, is connected with the thermo couple. The smallest temperature difference that can be detected by this system is (a) 16 (b) 12 (c) 8 (d) 20

Answer: (a). Minimum emf needed = IR = 10⁻⁵ × 40 = 4 × 10⁻⁴ V = 400 μ V. Δθ = (400)/(25 /) = 16° C So the answer is (a).

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Electrical Power & Heating Effect

The thermo $\text{e.m.f.}$ of a thermo -couple is $25\ \mu\text{V}/^\circ\text{C}$ at room temperature. A galvanometer of $40\text{ ohm}$ resistance, capable of detecting current as low as $10^{-5}\text{ A},$ is connected with the thermo couple. The smallest temperature difference that can be detected by this system is

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Answer: (a)

Minimum emf needed $= IR = 10^{-5} \times 40 = 4 \times 10^{-4}$ V $= 400\ \mu$ V.
$\Delta\theta = \frac{400\ \mu\text{V}}{25\ \mu\text{V}/^\circ\text{C}} = 16^\circ$ C
So the answer is (a).

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