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

Options

• Option A

  zero in the region r < a and inversely proportional to r in the region r > a

• Option B

  inversely proportional to r in the region r < a and uniform throughout in the region r > a

• Option C

  directly proportional to r in the region r < a and inversely proportional to r in the region r > a

• Option D

  uniform in the region r < a and inversely proportional to distance r from the axis, in the region r > a