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It is a physical constant, conventionally written as μ 0 (pronounced "mu nought" or "mu zero"). It quantifies the strength of the magnetic field induced by an electric current. Expressed in terms of SI base units, it has the unit kg⋅m⋅s −2 ⋅A −2. It can be also expressed in terms of SI derived units, N⋅A −2.
Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength, and it is rather weak. It typically requires a sensitive analytical balance to detect the ...
In physics, magnetic pressure is an energy density associated with a magnetic field. In SI units, the energy density of a magnetic field with strength can be expressed as = where is the vacuum permeability. Any magnetic field has an associated magnetic pressure contained by the boundary conditions on the field.
Between 1948 and 2019, the SI unit the ampere was defined by choosing the numerical value of μ 0 to be exactly 4 π × 10 −7 H/m. Similarly, since 1983 the SI metre has been defined relative to the second by choosing the value of c 0 to be 299 792 458 m/s .
The definitions for monopoles are of theoretical interest, although real magnetic dipoles can be described using pole strengths. There are two possible units for monopole strength, Wb (Weber) and A m (Ampere metre). Dimensional analysis shows that magnetic charges relate by q m (Wb) = μ 0 q m (Am).
where () is the electric field and () is the magnetic field, in phasor representation. The impedance is, in general, a complex number. In terms of the parameters of an electromagnetic wave and the medium it travels through, the wave impedance is given by
The magnetic field of larger magnets can be obtained by modeling them as a collection of a large number of small magnets called dipoles each having their own m. The magnetic field produced by the magnet then is the net magnetic field of these dipoles; any net force on the magnet is a result of adding up the forces on the individual dipoles.
The original law of Ampère states that magnetic fields relate to electric current. Maxwell's addition states that magnetic fields also relate to changing electric fields, which Maxwell called displacement current. The integral form states that electric and displacement currents are associated with a proportional magnetic field along any ...