Magnetic field near a straight wire
The magnetic field strength at a distance r from a long, straight current-carrying wire is proportional to:
Answer B: explanation for every choice
A
1/r² describes the electric field of a point charge.
B
Correct. B = μ₀I/(2πr), so the field increases with current and decreases with distance.
C
The field weakens with distance, not strengthens.
D
The field is proportional to current, not current squared.
TakeawayLong wire: B = μ₀I/(2πr).
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp82.