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A carbon resistor is marked with four colour bands. Reading the bands, the first two give significant figures 5 and 7, the third (multiplier) band corresponds to 10², and the fourth (tolerance) band is gold (±5%). What is the resistance value of the resistor?

1. (5700 ± 285) Ω
2. (7500 ± 750) Ω
3. (5700 ± 375) Ω
4. (7500 ± 375) Ω

Correct answer: (5700 ± 285) Ω

Solution

Green=5, Violet=7 give the significant figures 57. The red multiplier band gives 10², so R = 57 * 10² = 5700 Ω. The gold tolerance band is ±5%, so the uncertainty is 0.05 * 5700 = 285 Ω. Hence R = (5700 ± 285) Ω.

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