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Electromagnetic TheoryAmpere's Law

For an infinitely long straight conductor carrying current I in a medium of permeability mu, the magnetic flux density at radial distance r is?

  • Amu I/(2 pi r)
  • Bmu I/(4 pi r²)
  • CI r/(2 pi mu)
  • Dmu I r/2
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Correct Answer: A. mu I/(2 pi r)
Explanation: Using Ampere's law around a circular path gives H=I/(2πr), hence B=μI/(2πr).
Reference: Standard electromagnetic theory: ampere's law
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