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Poynting vector
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Poynting vector
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John Henry Poynting
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Poynting vector
Poynting vector The Poynting vector S is defined as to be equal to the cross product (1/μ)E × B, where μ is the magnetic permeability of the medium through which the radiation passes, E is the electric field, and B is the magnetic field.

Poynting vector

physics
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History

Poynting vector, quantity describing the magnitude and direction of the flow of energy in electromagnetic waves. It is named for English physicist John Henry Poynting, who introduced it in 1884.

The Poynting vector S is defined as to be equal to the cross product (1/μ)E × B, where μ is the magnetic permeability of the medium through which the radiation passes, E is the electric field, and B is the magnetic field. Applying the definition of cross product and the knowledge that the electric and magnetic fields are perpendicular to each other gives the magnitude S of the Poynting vector as (1/μ)EB, where E and B are, respectively, the magnitudes of the vectors E and B. The direction of the vector product S is perpendicular to the plane determined by the vectors E and B. For a traveling electromagnetic wave, the Poynting vector points in the direction of the propagation of the wave. The Poynting vector describes a power per unit area, and therefore its units are watts per square meter.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Erik Gregersen.