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Electromagnetic fields

Electromagnetic fields are electric and magnetic fields, which may change with time, for instance when charges are in motion. Moving charges produce a magnetic field in accordance with Ampère's circuital law (with Maxwell's addition), which, along with Maxwell's other equations, defines the magnetic field, B {\displaystyle \mathbf {B} }, in terms of its curl: ∇ × B = μ 0 (J + ε 0 ∂ E ∂ t), {\displaystyle \nabla \times \mathbf {B} =\mu _{0}\left(\mathbf {J} +\varepsilon _{0}{\frac {\partial \mathbf {E} }{\partial t}}\right),} where J {\displaystyle \mathbf {J} } is the current density, μ 0 {\displaystyle \mu _{0}} is the vacuum permeability, and ε 0 {\displaystyle \varepsilon _{0}} is the vacuum permittivity.