A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross section. The ratio of the magnetic field at a/2 and 2a from axis of the wire is:
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A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross section. The ratio of the magnetic field at a/2 and 2a from axis of the wire is:

G1 Physics · Accepted Answer

Inside a uniformly current-carrying wire: B(r) = μ₀Ir/(2πa²) At r = a/2: B₁ = μ₀I/(4πa) Outside the wire: B(r) = μ₀I/(2πr) At r = 2a: B₂ = μ₀I/(4πa) Therefore: B₁ : B₂ = 1 : 1