A long straight wire of radius a carries a steady current I uniformly distributed across its cross-section. Find the ratio of magnetic fields at radial distances a/2 and 2a from the axis, respectively.
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Question

A long straight wire of radius a carries a steady current I uniformly distributed across its cross-section. Find the ratio of magnetic fields at radial distances a/2 and 2a from the axis, respectively.

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G1 Physics · Accepted Answer

Step 1: Magnetic field at radius r inside a uniform solid conductor of radius a is B(inside)=μ₀Ir/(2πa²). Step 2: At r=a/2, B₁=μ₀I/(4πa); outside at r=2a, B₂=μ₀I/(4πa). Step 3: Thus field ratio B₁/B₂=1. Printed answer B. Final answer: (B) 1.