The Poynting vector describes the energy flux (J·m⁻²·s⁻¹) of an electromagnetic field. It is named after its inventor John Henry Poynting. Oliver Heaviside independently co-discovered the Poynting vector. In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks. ... This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ... Categories: People stubs | 1852 births | 1914 deaths | Physicists ... Oliver Heaviside (May 18, 1850 – February 3, 1925) was a self-taught English electrical engineer, mathematician, and physicist who adapted complex numbers to the study of electrical circuits, developed techniques for applying Laplace transforms to the solution of differential equations, reformulated Maxwells field equations in terms of electric and...

It points in the direction of energy flow and its magnitude is the power per unit area crossing a surface that is normal to it. It is derived by considering the conservation of energy and taking into account that the magnetic field can do no work. It is given the symbol S (in bold because it is a vector) and, in SI units, is given by: The magnitude of a mathematical object is its size: a property by which it can be larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs. ... In physics and in vector calculus, a spatial vector, or simply vector, is a concept characterized by a magnitude and a direction. ...

where E is the electric field, H and B are the magnetic field and magnetic flux density respectively, and μ is the permeability of the surrounding medium. For an electromagnetic wave propagating in free space μ becomes μ₀, the permeability of free space. It has been suggested that optical field be merged into this article or section. ... Current (I) flowing through a wire produces a magnetic field () around the wire. ... Current flowing through a wire produces a magnetic field (B, labeled M here) around the wire. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... This article is in need of attention. ...

For example, the Poynting vector near an ideally conducting wire is parallel to the wire axis - so electric energy is flowing in space outside of the wire. The Poynting vector becomes tilted toward wire for a resistive wire, indicating that energy flows from the e/m field into the wire, producing resistive Joule heating in the wire. In electronics, and in physics more broadly, Joule heating refers to the increase in temperature of a conductor as a result of resistance to an electrical current flowing through it. ...

Since the electric and magnetic fields of an electromagnetic wave oscillate, the magnitude of the Poynting vector also oscillates. The average of the magnitude over one period of the wave is called the irradiance or intensity, I: Periodicity is the quality of occurring at regular intervals (e. ... Irradiance, radiant emittance, and radiant exitance are radiometry terms for the power of electromagnetic radiation at a surface, per unit area. ...

For time-harmonic fields with some fixed frequency ω and time-dependence , the Poynting vector varies with the cosine-squared function, at twice the frequency of the electromagnetic wave. Since the average value of this function over one cycle is equal to half its peak value, the time-averaged power density is given by , where * denotes the complex conjugate.

S divided by the square of the speed of light in a vacuum is the density of the linear momentum of the electromagnetic field.

The time-averaged intensity <S> divided by the speed of light in a vacuum is the radiation pressure exerted by an electromagnetic wave on the surface of a target. Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ...

See also

• Poynting's theorem

Poyntings theorem is a statement due to John Henry Poynting about the conservation of energy for the electromagnetic field. ...

External links and references

• "Poynting Vector" from ScienceWorld (A Wolfram Web Resource) by Eric W. Weisstein
• Richard Becker, Electromagnetic Fields and Interactions, Dover Publications, 1964
• "Electromagnetic waves and the Poynting vector" Java applet from Blaze Labs Research