Dictionary Definition
flux
Noun
1 the rate of flow of energy or particles across
a given surface
2 a flow or discharge [syn: fluxion]
3 a substance added to molten metals to bond with
impurities that can then be readily removed
4 excessive discharge of liquid from a cavity or
organ (as in watery diarrhea)
5 a state of uncertainty about what should be
done (usually following some important event) preceding the
establishment of a new direction of action; "the flux following the
death of the emperor" [syn: state of
flux]
6 the lines of force surrounding a permanent
magnet or a moving charged particle [syn: magnetic
field, magnetic
flux]
7 (physics) the number of flux changes per unit
area [syn: flux
density]
8 in constant change; "his opinions are in flux";
"the newness and flux of the computer industry"
Verb
1 move or progress freely as if in a stream; "The
crowd flowed out of the stadium" [syn: flow]
3 mix together different elements; "The colors
blend well" [syn: blend,
mix, conflate, commingle, immix, fuse, coalesce, meld, combine, merge]
User Contributed Dictionary
English
Etymology
 From Latin fluxus, flow
Pronunciation
 Rhymes: ʌks
Noun
 A state of ongoing change.
 The schedule is in flux at the moment.
 A chemical agent for cleaning metal prior to soldering or welding.
 It is important to use flux when soldering or oxides on the metal will prevent a good bond.
 The rate of transfer of energy (or other physical
quantity) per unit area, specifically electric flux, magnetic flux.
 That high a neutron flux would be lethal in seconds.
Translations
A state of ongoing change
 Danish: forandring
 Dutch: voortdurende wijziging
 German: Fluss
A chemical agent for cleaning metal prior to
soldering or welding
 Danish: flusmiddel
 Dutch: flux , vloeimiddel
 German: Fließmittel
 Japanese: 融剤(ゆうざい, yūzai)
 Norwegian: Fluks
 Polish: topnik
The rate of transfer of energy (''electric flux,
magnetic flux)
French
Pronunciation
 lang=fr/fly/
 SAMPA: /fly/
Romanian
Noun
flux nExtensive Definition
In the various subfields of physics, there exist two common
usages of the term flux, both with rigorous mathematical
frameworks.
 In the study of transport phenomena (heat transfer, mass transfer and fluid dynamics), flux is defined as the amount that flows through a unit area per unit time. Flux in this definition is a vector.
 In the field of electromagnetism, flux is usually the integral of a vector quantity over a finite surface. The result of this integration is a scalar quantity. 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 first usage of flux, above. It has units of watts per square metre (Wm2)
One could argue, based on the work of James
Clerk Maxwell, that the transport definition precedes the more
recent way the term is used in electromagnetism. The specific quote
from Maxwell is "In the case of fluxes, we have to take the
integral, over a surface, of the flux through every element of the
surface. The result of this operation is called the surface
integral of the flux. It represents the quantity which passes
through the surface".
In addition to these common mathematical
definitions, there are many more loose usages found in fields such
as biology.
Transport phenomena
Flux definition and theorems
Flux is surface bombardment rate. There are many fluxes used in the study of transport phenomena. Each type of flux has its own distinct unit of measurement along with distinct physical constants. Six of the most common forms of flux from the transport literature are defined as: Momentum flux, the rate of transfer of momentum across a unit area (N·s·m2·s1). (Newton's law of viscosity,)
 Heat flux, the rate of heat flow across a unit area (J·m2·s1). (Fourier's law of convection) (This definition of heat flux fits Maxwell's original definition.)
 Chemical flux, the rate of movement of molecules across a unit area (mol·m2·s1). (Fick's law of diffusion)
 Volumetric flux, the rate of volume flow across a unit area (m3·m2·s1). (Darcy's law of groundwater flow)
 Mass flux, the rate of mass flow across a unit area (kg·m2·s1). (Either an alternate form of Fick's law that includes the molecular mass, or an alternate form of Darcy's law that includes the density)
 Radiative flux, the amount of energy moving in the form of photons at a certain distance from the source per steradian per second (J·m2·s1). Used in astronomy to determine the magnitude and spectral class of a star. Also acts as a generalization of heat flux, which is equal to the radiative flux when restricted to the infrared spectrum.
 Energy flux, the rate of transfer of energy through a unit area (J·m2·s1). The radiative flux and heat flux are specific cases of energy flux.
These fluxes are vectors at each point in space,
and have a definite magnitude and direction. Also, one can take the
divergence of any of
these fluxes to determine the accumulation rate of the quantity in
a control volume around a given point in space. For incompressible
flow, the divergence of the volume flux is zero.
Chemical diffusion
Flux, or diffusion, for gaseous molecules can be related to the function: \Phi = 2\pi\sigma_^2\sqrt
where:

 N is the total number of gaseous particles,
 k is Boltzmann's constant,
 T is the relative temperature in kelvins,
 \sigma_ is the mean free path between the molecules a and b.
Chemical molar flux of a component A in an
isothermal, isobaric system is also defined in
Ficks's first law as:
 \overrightarrow = D_ \nabla c_A
where:

 D_ is the molecular diffusion coefficient (m2/s) of component A diffusing through component B,
 c_A is the concentration (mol/m3) of species A.
This flux has units of
mol·m−2·s−1, and fits
Maxwell's original definition of flux.
Quantum mechanics
In quantum mechanics, particles of mass m in the state \psi(r,t) have a probability density defined as \rho = \psi^* \psi = \psi^2. \,
 \psi^2 d^3x. \,
 \mathbf = i \frac \left(\psi^* \nabla \psi  \psi \nabla \psi^* \right). \,
Electromagnetism
Flux definition and theorems
An example of the second definition of flux is the magnitude of a river's current, that is, the amount of water that flows through a crosssection of the river each second. The amount of sunlight that lands on a patch of ground each second is also a kind of flux.To better understand the concept of flux in
Electromagnetism, imagine a butterfly net. The amount of air moving
through the net at any given instant in time is the flux. If the
wind speed is high, then the flux through the net is large. If the
net is made bigger, then the flux would be larger even though the
wind speed is the same. For the most air to move through the net,
the opening of the net must be facing the direction the wind is
blowing. If the net opening is parallel to the wind, then no wind
will be moving through the net. (These examples are not very good
because they rely on a transport process and as stated in the
introduction, transport flux is defined differently than E+M flux.)
Perhaps the best way to think of flux abstractly is "How much stuff
goes through your thing", where the stuff is a field and the thing
is the imaginary surface.
As a mathematical concept, flux is represented by
the
surface integral of a vector field,
 \Phi_f = \int_S \mathbf \cdot \mathbf
where:

 E is a vector field of Electric Force,
 dA is the vector area of the surface S, directed as the surface normal,
 \Phi_f is the resulting flux.
The surface has to be orientable, i.e. two sides
can be distinguished: the surface does not fold back onto itself.
Also, the surface has to be actually oriented, i.e. we use a
convention as to flowing which way is counted positive; flowing
backward is then counted negative.
The surface normal is directed accordingly,
usually by the righthand
rule.
Conversely, one can consider the flux the more
fundamental quantity and call the vector field the flux
density.
Often a vector field is drawn by curves (field
lines) following the "flow"; the magnitude of the vector field is
then the line density, and the flux through a surface is the number
of lines. Lines originate from areas of positive divergence (sources) and end
at areas of negative divergence (sinks).
See also the image at right: the number of red
arrows passing through a unit area is the flux density, the
curve encircling the red
arrows denotes the boundary of the surface, and the orientation of
the arrows with respect to the surface denotes the sign of the
inner
product of the vector field with the surface normals.
If the surface encloses a 3D region, usually the
surface is oriented such that the outflux is counted positive; the
opposite is the influx.
The divergence
theorem states that the net outflux through a closed surface,
in other words the net outflux from a 3D region, is found by adding
the local net outflow from each point in the region (which is
expressed by the divergence).
If the surface is not closed, it has an oriented
curve as boundary. Stokes'
theorem states that the flux of the curl of a vector field is the
line
integral of the vector field over this boundary. This path
integral is also called
circulation, especially in fluid dynamics. Thus the curl is the
circulation density.
We can apply the flux and these theorems to many
disciplines in which we see currents, forces, etc., applied through
areas.
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.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.
Its integral form is:
 \oint_A \epsilon_0 \mathbf \cdot d\mathbf = Q_A
where:

 \mathbf is the electric field,
 d\mathbf is the area of a differential square on the surface A with an outward facing surface normal defining its direction,
 Q_A \ is the charge enclosed by the surface,
 \epsilon_0 \ is the permittivity of free space
 \oint_A is the integral over the surface A.
Either \oint_A \epsilon_0 \mathbf \cdot d\mathbf
or \oint_A \mathbf \cdot d\mathbf is called the electric
flux.
Faraday's law of induction in integral form is:
 \oint_C \mathbf \cdot d\mathbf = \int_ \ \cdot d\mathbf =  \frac
where:

 \mathrm\mathbf is an infinitesimal element (differential) of the contour C (i.e. a vector with magnitude equal to the length of the infinitesimal line element, and direction equal to the direction of the contour C).
The magnetic
field is denoted by \mathbf . Its flux is called the magnetic
flux. The timerate 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.
Poynting vector
The flux of the Poynting vector through a surface is the electromagnetic power, or energy per unit time, passing through that surface. This is commonly used in analysis of electromagnetic radiation, but has application to other electromagnetic systems as well.Biology
In general, 'flux' in biology relates to movement of a substance between compartments. There are several cases where the concept of 'flux' is important. The movement of molecules across a membrane: in this case, flux is defined by the rate of diffusion or transport of a substance across a permeable membrane. Except in the case of active transport, net flux is directly proportional to the concentration difference across the membrane, the surface area of the membrane, and the membrane permeability constant.
 In ecology, flux is often considered at the ecosystem level  for instance, accurate determination of carbon fluxes using techniques like eddy covariance (at a regional and global level) is essential for modeling the causes and consequences of global warming.
 Metabolic flux refers to the rate of flow of metabolites along a metabolic pathway, or even through a single enzyme. A calculation may also be made of carbon (or other elements, e.g. nitrogen) flux. It is dependent on a number of factors, including: enzyme concentration; the concentration of precursor, product, and intermediate metabolites; posttranslational modification of enzymes; and the presence of metabolic activators or repressors. Metabolic control analysis and flux balance analysis provide frameworks for understanding metabolic fluxes and their constraints.
See also
 Explosively pumped flux compression generator
 Fast Flux Test Facility
 Flux capacitor
 Fluid dynamics
 Flux quantization
 Flux pinning
 Gauss's law
 Inversesquare law
 Latent heat flux
 Luminous flux
 Magnetic flux
 Magnetic flux quantum
 Neutron flux
 Poynting flux
 Poynting theorem
 Radiant flux
 Rapid single flux quantum
 Sound energy flux
 Volumetric flow rate
 Fluence (flux for particle beams)
 Flux footprint
References
Further reading
flux in German: Fluss (Physik)
flux in Modern Greek (1453): Ροή
flux in Esperanto: Fluo
flux in Persian: شار
flux in Italian: Flusso
flux in Hebrew: שטף
flux in Japanese: フラックス (物理学)
flux in Norwegian: Fluks
flux in Polish: Strumień pola
flux in Portuguese: Fluxo (física)
flux in Simple English: Flux
flux in Finnish: Sähkövuo
flux in Vietnamese: Thông lượng
flux in Ukrainian: Густина потоку енергії
flux in Urdu: سیلان
Synonyms, Antonyms and Related Words
ASA scale, BM, British candle, Brownian
movement, Hefner candle, Scheiner scale, abscess, add, advance, affluence, afflux, affluxion, ague, amalgamate, anemia, angular motion, ankylosis, anoxia, anticoagulant, apnea, ascending, ascent, asphyxiation, assimilate, asthma, ataxia, atrophy, axial motion, backache, backflowing, backing, backward motion,
bandage, bathe, bleeding, blend, blennorhea, bloody flux,
bougie decimale, bowel movement, cachexia, cachexy, candle, candle lumen, candle
power, candlefoot, candlehour, candlemeter, cardialgia, care for,
career, catharsis, change, chill, chills, china clay, china stone,
cholera morbus, chylifaction, chylification, clay, climbing, coalesce, colic, colliquate, combine, come together, compound, comprise, concourse, confluence, conflux, connect, consolidate, constipation, convulsion, costiveness, coughing, course, crap, crosscurrent, cure, current, cut, cyanosis, decimal candle,
decoagulate,
decoct, defecation, defluxion, defrost, dejection, deliquesce, descending, descent, diagnose, diarrhea, diluent, dilutant, direct tide, discharge, dissolve, dissolvent, dissolving agent,
dizziness, doctor, downflow, downpour, downward motion,
drift, driftage, dropsy, dysentery, dyspepsia, dyspnea, ebb, ebb and flow, ebb tide,
ebbing, edema, effusion, egestion, ejaculation, ejection, elimination, emaciation, embody, emission, encompass, evacuation, excretion, exposure meter,
extravasation,
extrusion, exudation, fainting, fatigue, fever, fibrillation, fireclay, flight, flood, flood tide, flow, flowing, fluctuation, fluency, fluidify, fluidity, fluidize, fluidness, flux and reflux,
fluxility, fluxion, footcandle, forward
motion, full tide, fuse,
give care to, glaze,
gripe, gripes, growth, gush, heal, heartburn, hemorrhage, high blood
pressure, high tide, high water, hydrops, hypertension, hypotension, icterus, include, incorporate, indecision, indecisiveness, indigestion, inflammation, inflow, infuse, insomnia, instability, integrate, intensity, interblend, interfuse, international
candle, irregularity, itching, jaundice, join, juiciness, kaolin, labored breathing,
lactation, lactescence, lamphour,
leach, lientery, light, light meter, light quantum,
liquefacient,
liquefaction,
liquefier, liquefy, liquesce, liquidize, liquidness, lixiviate, loose bowels, low
blood pressure, low tide, low water, lumbago, lumen, lumen meter, lumenhour,
lumeter, luminous flux,
luminous intensity, luminous power, lump together, lunar tide,
lux, make one, marasmus, massage, meld, melt, melt down, melt into one,
merge, milkiness, mill run, millrace, minister to, mix, modification, moisture, motion, mounting, movement, mutation, nasal discharge,
nausea, neap, neap tide, necrosis, nurse, oblique motion, obstipation, ongoing, onrush, onward course, operate
on, opposite tide, oscillation, outflow, pain, paralysis, passage, percolate, petuntse, photon, physic, plaster, plunging, porcelain clay,
poultice, progress, pruritus, purgation, purge, put together, pyrosis, quantum, race, radial motion, random motion,
rash, reembody, refine, reflowing, refluence, reflux, refractory clay, regression, remedy, render, resolutive, resolvent, retrogression, rheum, rheuminess, rip, riptide, rising, roll into one, rub, run, runs, rush, sappiness, sclerosis, secretion, seizure, serosity, set, shade into, shit, shits, shock, sideward motion, sinking, skin eruption, slip, smelt, sneezing, soaring, solar tide, solidify, solubilize, solve, solvent, sore, spasm, spate, splint, spring tide, sternway, stool, strap, stream, subsiding, succulence, suppuration, surge, swing, swinging, syncretize, syndicate, synthesize, tabes, tachycardia, thalassometer, thaw, thin, thinner, tidal amplitude, tidal
current, tidal current chart, tidal flow, tidal range, tide, tide chart, tide gate, tide
gauge, tide race, tide rip, tidewater, tideway, traject, trajet, transudation, treat, trend, trots, tumor, turistas, unclot, undercurrent, undertow, unfreeze, unify, unit of flux, unit of
light, unite, unrest, upset stomach, upward
motion, vertigo,
voidance, vomiting, wasting, water flow, wateriness, wavering