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出典:『Wikipedia』 (2011/06/14 15:45 UTC 版)

英語による解説

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In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.

• Generally, in particular in the field of electromagnetism and mathematics, flux is usually the integral of a vector quantity, flux density, over a finite surface. It is an integral operator that acts on a vector field similarly to the gradient, divergence and curl operators found in vector analysis. The result of this integration is a scalar quantity called flux. The magnetic flux is thus the integral of the magnetic vector field B over a surface, and the electric flux is defined similarly. Using this definition, the flux of the Poynting vector over a specified surface is the rate at which electromagnetic energy flows through that surface. Confusingly, the Poynting vector is sometimes called the power flux, which is an example of the second usage of flux, below. It has units of watts per square metre (W/m²)
  In this context, flux has a primary mathematical definition in terms of a surface integral which uses the vectors that represent the force which is causing the flux being studied: