Retarded source electric and magnetic fields
Differentiating the causal potentials gives E=(1/(4πε₀))∫([ρ]n/R²+[ρ̇]n/(cR)−[J̇]/(c²R))d³r′ and B=(μ₀/(4π))∫([J]/R²+[J̇]/(cR))×n d³r′.
Key knowledge
Differentiating the causal potentials gives E=(1/(4πε₀))∫([ρ]n/R²+[ρ̇]n/(cR)−[J̇]/(c²R))d³r′ and B=(μ₀/(4π))∫([J]/R²+[J̇]/(cR))×n d³r′. Here brackets mean source evaluation at t−R/c and n=(r−r′)/R; the time derivatives are taken at the source before retarded evaluation.
Values and equations
E=1/(4πε₀)∫([ρ]n/R²+[ρ̇]n/(cR)−[J̇]/(c²R))d³r′; B=μ₀/(4π)∫([J]/R²+[J̇]/(cR))×n d³r′
- E
- Electric field V m⁻¹
- B
- Magnetic flux density T
- r,r′,R
- Positions/separation m
- n
- Unit direction from source to observer
- ρ,ρ̇
- Charge density and its source-time derivative; C m⁻³ and C m⁻³ s⁻¹
- J,J̇
- Current density and its source-time derivative; A m⁻² and A m⁻² s⁻¹
- c
- Vacuum light speed m s⁻¹
- ε₀
- Vacuum permittivity F m⁻¹
- μ₀
- Vacuum permeability H m⁻¹
- t
- Time s
Conditions and scope
- Sufficiently regular conserved localized vacuum sources, retarded all-space source-only solution and convergent integrals; add free fields for independent homogeneous initial data.
- Retarded position dependence must be included when differentiating. The static terms alone are not a time-dependent Coulomb/Biot–Savart solution; material interfaces and singular ideal point sources require their corresponding treatment.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Classical Electromagnetism (2014): Retarded fields: Equations 77–86: differentiate retarded time in spatial gradients and obtain both source-field integrals. Maxwell equations: Efimenko source-field derivation (2018): Printed pages 14–16, equations 76–84: source-time derivative chain rule, magnetic current/cross-product order and all three electric-field terms. Uses the correct final field integrals rather than the earlier duplicated-4π potential typo.
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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