JEE Mains · Physics · STD 12 - 4. Moving charges and magnetism
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
- A Zero in the region \(r < a\) and inversely proportional to \(r\) in the region \(r > a\)
- B Inversely proportional to \(r\) in the region \(r < a\) and uniform throughout in the region \(r > a\)
- C Directly proportional to \(r\) in the region \(r < a\) and inversely proportional to \(r\) in the region \(r > a\)
- D Uniform in the region \(r < a\) and inversely proportional to distance \(r\) from the axis, in the region \(r > a\)
Answer & Solution
Correct Answer
(C) Directly proportional to \(r\) in the region \(r < a\) and inversely proportional to \(r\) in the region \(r > a\)
Step-by-step Solution
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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