Localized-current magnetic dipole
For a localized steady conserved current, the magnetic dipole moment is m=(1/2)∫r′×J(r′)d³r′.
Key knowledge
For a localized steady conserved current, the magnetic dipole moment is m=(1/2)∫r′×J(r′)d³r′. Its leading exterior far-distance potential is A≈μ₀(m×r)/(4πr³), giving B≈μ₀[3n(m·n)−m]/(4πr³), n=r/r. A small planar current loop has m=I a, with oriented area vector a.
Values and equations
m=½∫r′×J d³r′; A≈μ₀(m×r)/(4πr³); B≈μ₀[3n(m·n)−m]/(4πr³)
- m
- Magnetic dipole moment A m²
- r,r′
- Observer/source positions m
- r
- Observation distance m
- n
- Radial unit vector
- J
- Steady current density A m⁻²
- A
- Magnetic vector potential T m
- B
- Magnetic flux density T
- μ₀
- Vacuum permeability H m⁻¹
- I
- Loop current A
- a
- Oriented loop area m²
Conditions and scope
- Magnetostatic localized divergence-free current, origin within the source region, all-space vacuum and observation distance much larger than source size; this is the leading nonvanishing multipole if m≠0.
- The displayed field is exterior and excludes r=0. It does not specify a point-dipole contact distribution, extended-source interior field or time-dependent radiative dipole; higher multipoles can matter when the leading moment vanishes.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Electromagnetism (2014): Localized current distribution: Equations 661–677 and 679: 1/r expansion, current antisymmetry, integral moment, exterior vector potential/field and planar loop. The integrated moment is used without interpreting r′×J/2 as a universal local material magnetization.
2026-10-10 · Independent AI editorial review: All 136 unique authored Physics compact statements, all hypotheses and displayed equations/variable/units tables, all 192 Physics-origin semantic links, exact 165 author inspection matrix and mapped retained conceptual claims have been independently read. Three Physics-tagged Measurement realization records are delegated to root Measurement review. Scientific source verification combines exact author section inspection with independent whole compact-content/semantic review and targeted primary rechecks recorded below; it does not claim each full source body was independently reread. Independent AI editorial review is not human specialist certification or experimental replication. Field inventory is approved after independently reviewing the two added source-inspected band-construction methods. Receipt: physics-independent-content-inventory-review.1.
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