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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Correct Answer

(C) Directly proportional to \(r\) in the region \(r < a\) and inversely proportional to \(r\) in the region \(r > a\)

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Detailed explanation

\(B = \begin{cases}\frac{\mu_0 Ir }{\pi a ^2} & r \leq a \\ \frac{\mu_0 I }{\pi r ^2} & r \geq a \end{cases}\)

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