Flux

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For the metalurgical definition see Flux (metallurgy); for the definition in psychology, see Flow (psychology); for the book by Stephen Baxter see Flux (book)

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 F_N 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. (See also flux unit).

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.