A copper wire 200 m long has a resistance of 21 Ω and a diameter of 0.44 mm. Approximately what is its specific resistance?
Correct answer A. 1.6 × 10^-8 Ω·m
Explanation
Resistivity ρ = RA/l. The area is π(0.22 × 10^-3)² ≈ 1.52 × 10^-7 m², so ρ = 21 × 1.52 × 10^-7 / 200 ≈ 1.6 × 10^-8 Ω·m.
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