Poynting vector
Noun
Meaning
Poynting vector (plural Poynting vectors)
(electromagnetism) The vector obtained in the direction of a right-hand screw from the cross product (vector product) of the electric field vector rotated into the magnetic field vector of an electromagnetic wave. Note: The Poynting vector, with transmission media parameters and constants, gives the irradiance and direction of propagation of the electromagnetic wave. Mathematically:
P
→
=
E
→
×
H
→
{\displaystyle {\vec {P}}={\vec {E}}\times {\vec {H}}}
.
Related terms
Examples
Although there are only static electric and magnetic fields, the calculation of the Poynting vector produces a clockwise circular flow of electromagnetic energy, with no beginning or end.
Antenna (radio) An isotropic antenna is an idealized " radiating element " used as a reference ; an antenna that broadcasts power equally (calculated by the Poynting vector ) in all directions.
Classical picture In classical Maxwell electrodynamics a phase-conjugating mirror performs reversal of the Poynting vector : : which is a linear momentum density of electromagnetic field, where (in) means incident field, (out) means reflected field.
Confusingly, the Poynting vector is sometimes called the power flux, which is an example of the first usage of flux, above.
For example, the Poynting vector within the dielectric insulator of a coaxial cable is nearly parallel to the wire axis (assuming no fields outside the cable and a wavelength longer than the diameter of the cable, including DC).
In the region around the battery the Poynting vector is directed outward, indicating power flowing out of the battery into the fields; in the region around the resistor the vector is directed inward, indicating field power flowing into the resistor.