The specific resistance ρ of a metre-bridge wire of length 1 m, diameter 0.12 cm and resistance 1.49 Ω is approximately:
A$1.68 \times 10^{-6}$ Ω·m
B$1.49 \times 10^{-2}$ Ω·m
C$1.49 \times 10^{-6}$ Ω·m
D$1.68 \times 10^{-4}$ Ω·m
Answer & Solution
Correct answer: A. $1.68 \times 10^{-6}$ Ω·m
$\rho = R\pi r^2/L = 1.49 \times \pi \times (0.06\times10^{-2})^2/1 \approx 1.68\times10^{-6}$ Ω·m. Typical of a metallic alloy like manganin/constantan.
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