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A bulb filament has a resistance of 100 Ω at 100°C. If the temperature coefficient of resistance is 0.005 per °C, at what temperature will its resistance rise to 200 Ω?

1. 300°C
2. 400°C
3. 500°C
4. 200°C

Correct answer: 400°C

Solution

200/100 = (1+0.005*T2)/(1+0.005*100) = (1+0.005*T2)/1.5, so 1+0.005*T2 = 3, giving T2 = 400 C.

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