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In the old "electromagnetic (emu)" system of units, defined in the late 19th century, k m was chosen to be a pure number equal to 2, distance was measured in centimetres, force was measured in the cgs unit dyne, and the currents defined by this equation were measured in the "electromagnetic unit (emu) of current", the "abampere". A practical ...
Values shown above are approximate and valid only at the magnetic fields shown. They are given for a zero frequency; in practice, the permeability is generally a function of the frequency. When the frequency is considered, the permeability can be complex , corresponding to the in-phase and out of phase response.
These equations taken together are as powerful and complete as Maxwell's equations. Moreover, the problem has been reduced somewhat, as the electric and magnetic fields together had six components to solve for. [1] In the potential formulation, there are only four components: the electric potential and the three components of the vector potential.
Lorentz force on a charged particle (of charge q) in motion (velocity v), used as the definition of the E field and B field. Here subscripts e and m are used to differ between electric and magnetic charges. The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths.
The impedance of free space (that is, the wave impedance of a plane wave in free space) is equal to the product of the vacuum permeability μ 0 and the speed of light in vacuum c 0. Before 2019, the values of both these constants were taken to be exact (they were given in the definitions of the ampere and the metre respectively), and the value ...
Some observed electromagnetic phenomena cannot be explained with Maxwell's equations if the source of the electromagnetic fields are the classical distributions of charge and current. These include photon–photon scattering and many other phenomena related to photons or virtual photons , " nonclassical light " and quantum entanglement of ...
In free space the wave impedance of plane waves is: = (where ε 0 is the permittivity constant in free space and μ 0 is the permeability constant in free space). Now, since = = (by definition of the metre),
List of equations in classical mechanics; Table of thermodynamic equations; List of equations in wave theory; List of relativistic equations; List of equations in fluid mechanics; List of electromagnetism equations; List of equations in gravitation; List of photonics equations; List of equations in quantum mechanics; List of equations in ...