$A$ 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 $r > a$

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