The magnetic field at a distance r from a long straight current-carrying wire is:
Aμ0 I r/(2π)
Bμ0 I/(2r)
Cμ0 I/(2πr)
Dμ0 I² r
Answer & Solution
Correct answer: C. μ0 I/(2πr)
Ampere's law gives B = μ0 I/(2πr).
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