Flux

:This article is about the concept of flux in science and mathematics. For other uses of the word, see flux (disambiguation).

Flux in physics

Maxwell's equations

The flux of electric and magnetic field lines is frequently discussed in electrostatics. This is because in Maxwell's equations in integral form involve integrals like above for electric and magnetic fields.

Related Topics:
Electric - Magnetic field - Electrostatics - Maxwell's equations

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For instance, Gauss's law states that the flux of the electric field out of a closed surface is proportional to the electric charge enclosed in the surface (regardless of how that charge is distributed). The constant of proportionality is the reciprocal of the permittivity of free space.

Related Topics:
Gauss's law - Electric charge - Permittivity

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Its integral form is:

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: oint_A epsilon_0 mathbf{E} cdot dmathbf{A} = Q_A

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where mathbf{E} is the electric field, dmathbf{A} is the area of a differential square on the surface A with an outward facing surface normal defining its direction, Q_mbox{A} is the charge enclosed by the surface, epsilon_0 is the permittivity of free space and oint_A is the integral over the surface A.

Related Topics:
Surface normal - Permittivity

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Either oint_A epsilon_0 mathbf{E} cdot dmathbf{A} or oint_A mathbf{E} cdot dmathbf{A} is called the electric flux.

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Faraday's law of induction in integral form is:

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:oint_C mathbf{E} cdot dmathbf{l} = -int_{partial C} {dmathbf{B}over dt} cdot dmathbf{s} = - rac{d Phi_D}{ d t}

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The magnetic field density, also called magnetic flux density, is denoted by mathbf{B} . Its flux is called the magnetic flux. The time-rate of change of the magnetic flux through a loop of wire is minus the electromotive force created in that wire. The direction is such that if current is allowed to pass through the wire, the electromotive force will cause a current which "opposes" the change in magnetic field by itself producing a magnetic field opposite to the change. This is the basis for inductors and many electric generators.

Related Topics:
Magnetic field density - Magnetic flux - Electromotive force - Inductor - Electric generator

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Electromagnetic radiation

For electromagnetic radiation, the flux of the Poynting vector through a surface is the power, or energy per unit time, passing through that surface.

Related Topics:
Electromagnetic radiation - Poynting vector - Power - Energy - Time

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Fluid systems

In fluid systems the flux is the volumetric flow rate or rate of fluid flow.

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In fluid dynamics, flux is a physical rate process defined as the rate of flow or transfer of a physical quantity through an area per time. It is a key concept used in understanding fluid dynamics and related transport phenomena.

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There are three basic fluxes used in the study of transport phenomena. Each type of flux has its own distinct unit of measurement along with distinct physical constants. The three basic forms of flux are defined as:

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• Momentum flux, the rate of momentum in and out of the system.
• Heat flux, the rate of heat transfer.
• Mass flux, the rate of mass transfer.

When dealing with one-dimensional flux, the fundamental laws that govern this process include:

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• Newton's Law of Viscosity
• Fourier's Law of Convection
• Fick's Law of Diffusion.