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A coil has a temperature coefficient of resistance of 0.005 per degree Celsius. At 20 deg C, a current of 2 A flows through it when a potential difference of 10 V is applied. Find the current through the same coil at 40 deg C when the same potential difference is applied.

1. 5/3 A
2. 20/11 A
3. 10/7 A
4. 25/13 A

Correct answer: 20/11 A

Solution

The resistance at 20 deg C is R0 = V/I = 10/2 = 5 ohm. At 40 deg C, R = R0 * (1 + alpha * delta_T) = 5 * (1 + 0.005 * 20) = 5.5 ohm. The new current I = V/R = 10/5.5 = 20/11 A.

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