alleryMagnetic field at distance r from a long straight current-carrying wire:
Aμ₀ I / (2πr)
Bμ₀ I / (4πr)
Cμ₀ I r / 2π
Dμ₀ I² / (2πr)
Answer & Solution
Correct answer: A. μ₀ I / (2πr)
**By Ampere's law:** B = μ₀ I / (2πr).
Inversely proportional to distance r.
Magnetic field circles around the wire (right-hand rule).
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