Energy flux
Encyclopedia
Energy flux is the rate of transfer of energy
through a surface. The quantity is defined in two different ways, depending on the context:
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
through a surface. The quantity is defined in two different ways, depending on the context:
- Rate of energy transfer per unit areaAreaArea is a quantity that expresses the extent of a two-dimensional surface or shape in the plane. Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat...
. (SI units: W·m-2 = J·m-2·s-1)- This is a vector quantity, its components being determined in terms of the normal (perpendicular) direction to the surface of measurement.
- This is sometimes called energy flux densityFlux density-Formal Statement:The flux density is simply defined as the amount of flux passing through a unit-area. -Mathematical Statement:The flux density would essentially be the number of field lines passing through a defined unit-area...
, to distinguish it from the second definition. - Radiative fluxRadiative fluxRadiative flux, or radiative flux density, is the amount of power radiated through a given area, in the form of photons or other elementary particles, typically measured in W/m2. It is used in astronomy to determine the magnitude and spectral class of a star...
, heat fluxHeat fluxHeat flux or thermal flux is the rate of heat energy transfer through a given surface. The SI derived unit of heat rate is joule per second, or watt. Heat flux is the heat rate per unit area. In SI units, heat flux is measured in W/m2]. Heat rate is a scalar quantity, while heat flux is a vectorial...
, and sound energy flux are specific cases of energy flux density.
- Total rate of energy transfer. (SI units: W = J·s-1)
- This is sometimes informally called energy currentEnergy currentEnergy current is a flow of energy defined by the Poynting vector , as opposed to normal current . It was originally postulated by Oliver Heaviside.- Explanation :...
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- This is sometimes informally called energy current