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A copper wire is wound on a wooden frame, whose shape is that of an equilateral triangle. If the linear dimension of each side of the frame is increased by a factor of 3, keeping the number of turns of the coil per unit length of the frame the same, then the self inductance of the coil:

1. decreases by a factor of 3 9
2. increases by a factor of 27
3. decreases by a factor of 9
4. increases by a factor of 3

Correct answer: increases by a factor of 27

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