alleryMagnetic field at a point on the axis of a circular loop, far from the loop (distance x ≫ R), behaves as:
AB ∝ 1 / x³
BB ∝ 1 / x²
CB ∝ 1 / x
DB ∝ x
Answer & Solution
Correct answer: A. B ∝ 1 / x³
1. Far from the loop, the magnetic field along the axis is that of a magnetic DIPOLE.
2. For a dipole, on the axis B ∝ 1/x³.
3. Compare: electric dipole field also goes as 1/r³ far away.
_Source: syllabus Physics Ch 4 §4.6 (axial field large-x limit)_
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