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A long, straight conductor of radius a carries a constant current I that is spread uniformly over its cross-sectional area. What is the ratio of the magnetic field at a distance a/2 from the axis to the magnetic field at a distance 2a from the axis?

1. 1/2
2. 1/4
3. 4
4. 1

Correct answer: 1

Solution

The magnetic field inside a long, straight conductor increases linearly with distance from the center, while outside the conductor, it decreases with the distance from the axis. At a distance a/2, the magnetic field is proportional to the distance from the center, while at 2a, it behaves inversely with distance, leading to a ratio of 1.

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