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In electrodynamics, Poynting's theorem is a statement of conservation of energy for electromagnetic fields developed by British physicist John Henry Poynting. [1] It states that in a given volume, the stored energy changes at a rate given by the work done on the charges within the volume, minus the rate at which energy leaves the volume.
The Poynting vector appears in Poynting's theorem (see that article for the derivation), an energy-conservation law: =, where J f is the current density of free charges and u is the electromagnetic energy density for linear, nondispersive materials, given by = (+), where
For the special case of = , this gives a re-statement of conservation of energy or Poynting's theorem (since here we have assumed lossless materials, unlike above): The time-average rate of work done by the current (given by the real part of ) is equal to the time-average outward flux of power (the integral of the Poynting vector). By the same ...
In gravity, a hollow sphere has a three-dimensional equipotential region inside, with no gravity from the sphere (see shell theorem). In electrostatics, a conductor is a three-dimensional equipotential region. In the case of a hollow conductor (Faraday cage [4]), the equipotential region includes the space inside.
Poynting may refer to: John Henry Poynting (1852–1914), a British physicist, after whom are named: Poynting vector, a representation of the energy flux of an electromagnetic field; Poynting's theorem on conservation of energy in electromagnetic field; Poynting (lunar crater), crater on the Moon; Poynting (Martian crater), crater on Mars
Phenomenological equations are derived for electromagnetic field in the gain medium, i.e. Maxwell's equations for the gain medium, and Poynting's theorem for these equations. [1] [2] [5] Maxwell's equations in the gain medium are used to obtain equations for energy flux, and to describe nonlinear phase effect. [1] [2] [5]
Mason Science College (demolished in 1964) John Henry Poynting FRS [1] (9 September 1852 – 30 March 1914 [2] [3]) was an English physicist.He was the first professor of physics at Mason Science College from 1880 to 1900, and then the successor institution, the University of Birmingham until his death.
All but the last term of can be written as the tensor divergence of the Maxwell stress tensor, giving: = +, As in the Poynting's theorem, the second term on the right side of the above equation can be interpreted as the time derivative of the EM field's momentum density, while the first term is the time derivative of the momentum density for ...