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A long straight wire of circular cross-section of radius a carries a steady current 1. The current is uniformly distributed across its cross-section. The ratio of the magnitudes of magnetic field at a point al2 above the surface of the wire to that at a point distant al2 below its surface is :
The correct answer is (B) 1 : 1.
The magnetic field outside a long straight current-carrying wire depends only on the distance from the center and not on the position relative to the surface. Hence, the field at equal distances above and below the surface is the same.
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