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A coil of one turn is made of a wire of certain length and then from the same length a coil of two turns is made. If the same current is passed in both the cases, then the ratio of the magnetic inductions at their centres will be

1. 2:1
2. 1:4
3. 4:1
4. 1:2

Correct answer: 4:1

Solution

The magnetic field at the center of a circular coil is directly proportional to the square of the number of turns (n²) for the same current and wire length. For one turn, n = 1, and for two turns, n = 2. The ratio of magnetic inductions is (2²):(1²) = 4:1.

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