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A carbon resistor rated at 2 W carries the colour bands green, black, red and brown (in that order). What is the largest current that may safely flow through it?

1. 63 mA
2. 0.4 mA
3. 100 mA
4. 20 mA

Correct answer: 20 mA

Solution

The resistance is 5000 ohm; with a 2 W limit, I = sqrt(P/R) = sqrt(2/5000) = 0.02 A.

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