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Flux is a common phenomenon throughout the natural world and has become a ubiquitous concept throughout physics and mathematics, and hence technology. Flux describes the flow of a physical property through space and is often coupled with a time variation. There are two common usages or contexts for flux, each having solid mathematical frameworks – flux as a vector in the context of transport phenomena and flux as a scalar quantity in the context of electromagnetism.
Flux is a general term which refers to the flow of a physical quantity through space such as electromagnetic waves. The word comes from the Latin word "fluxus," which means flow and was first introduced by Isaac Newton into differential calculus as "fluxion."
In transport phenomena such as heat transfer and fluid dynamics, flux is considered the "rate of flow of a property per unit area," which has the dimension of quantity and time. For example, the amount of water flowing per square area of a river and the amount of light that hits an area per second are considered types of flux.
Examples of transport fluxes include:
In electromagnetism, force fields and like phenomena, flux is considered as a surface integral and is the energy that flows around or through an electrically charged object. In this case, the simplest way to think of flux is the amount of air moving through a tube. If the wind speed is high and the tube opening (the area) remains constant, the amount of air that flows through is greater. In order to maintain the air speed and increase the amount of air flowing through, then the opening must be enlarged. The flux density is simply how close flux lines are to each other. In the first scenario where there is a smaller tube opening, the flux density is bigger, while when the area of the opening is increased, the flux density becomes less because each flux line is further from each other or from the radiating object, while the quantity remains constant.