A long straight wire of circular cross-section (radius a) is carrying steady current I. The current I is uniformly distributed across this cross-section. The magnetic field is
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A long straight wire of circular cross-section (radius a) is carrying steady current I. The current I is uniformly distributed across this cross-section. The magnetic field is

G1 Physics · Accepted Answer

For a long solid wire of radius a carrying uniformly distributed current I: For r < a, the enclosed current is I(enclosed) = I(r²/a²) Using Ampere's law: B(2πr) = μ₀I(enclosed) So, B = μ₀Ir/(2πa²) Hence B ∝ r inside the wire. For r > a: B = μ₀I/(2πr) Hence B ∝ 1/r outside. Therefore option C follows.