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Flux

Electromagnetics

Flux is the flow that occurs as a result of a potential difference. It can be described as a through variable, where potential difference is the across variable. The product of the flux and the potential difference is the power, which is the rate of change of the conserved quantity, e.g energy.

There are many types of flux:

• In electrical engineering the flux is the electrical current or the magnetic current.
• In mechanical systems the momentum flux is the force.
• In fluid systems the flux is the rate of fluid flow.
• In thermal systems the flux is the rate of heat flow.

Flux is a quantity proportional to the surface integral of the normal (perpendicular) force field intensity over a given surface.

Where FN is the normal component of a field (eg, gravitational field, magnetic field, electric field) and K is the constant of proportionality between the field and the flux density (permittivity, permeability, etc.).

For electromagnetic radiation, flux signifies the energy per unit time (or power) passing through a surface.

The term is also used to denote the volume or mass of fluid or particles transferred across a given area perpendicular to the direction of flow in a given time. For photons or particles, flux is the number passing through a surface per unit time. In nuclear physics, flux commonly means the product n×v, where n is the number of particles per unit volume and v is their mean velocity.

Metallurgy

Flux is an aid to melting, a material which by its chemical action facilitates soldering or brazing of metals. Such a flux applied to a metallic surface cleans it and renders it receptive to amalgamation with the solder or brazing metal. Some fluxes are rosin, for soldering tin; muriatic acid, for galvanized iron and other zinc surfaces; and borax, for brazing.

A related use of the term flux is to designate the material added to the contents of a smelting furnace or a cupola for the purpose of purging the metal of impurities, and of rendering the slag more liquid. The flux most commonly used in iron and steel furnaces is limestone, which is charged in the proper proportions with the iron and fuel. The slag is a liquid mixture of ash, flux, and other impurities.