A metal coil has resistance 20 Ω at 20 °C and 24 Ω at 120 °C. Taking 20 °C as the reference, what is its temperature coefficient of resistance?
Correct answer C. 2.0 × 10⁻³ K⁻¹
Explanation
α = (R₂ − R₁)/(R₁ΔT) = (24 − 20)/(20 × 100) = 2.0 × 10⁻³ K⁻¹. Using 120 instead of the temperature change of 100 K gives the wrong value of 1.7 × 10⁻³ K⁻¹.
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