What is Flux: Definition and 1000 Discussions

Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. A flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport phenomena, flux is a vector quantity, describing the magnitude and direction of the flow of a substance or property. In vector calculus flux is a scalar quantity, defined as the surface integral of the perpendicular component of a vector field over a surface.

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  1. A

    Why do electric flux and charge have the same units?

    eletric flux and charge have same units ie coloumb is it a coincidence or some similarity exists btw these two? electric flux density D= εE is used for calculating flux ψ not E .why?(read tht it is done for practical reasons) please explain the practical reasons ,if any.
  2. S

    Air gap flux density in DC machine

    Why is it that the air gap flux density is flat topped at no load. What happens to it's shape when machine is loaded?
  3. S

    The dispersion (standard deviation) of the estimator of neutron flux number

    Hello people, I think the problem what I have is well known in experimental physics. Hope, somebody can helps me, thanks in advance. Here is: There is a source of neutrons with a flux of λ neutrons per minute, which you do not know and want to estimate. You open the detector for one minute...
  4. O

    Electric flux, vector or scalar?

    I know that the electric flux is a scalar quantity, but the concept of the Electric flux seems to confused me. If the electric flux density is a vector quantity, how come the electric flux is a scalar quantity? For example, I have the electric flux density: D=20i+2j. Isn't it means...
  5. S

    How can I calculate the visual magnitude of a star with only its flux data?

    How to calculate the visual magnitude of a star having only the flux of such star? The equation involves 2 magnitudes and 2 fluxes, corresponding to 2 objects a and b: ma-mb= -2.5log10\left( \frac{F_a}{F_b}\right) but I just have Fa and I have to obtain ma. Is it valid to take...
  6. M

    Flux Equations for a Solid Surface and a Curve

    are both of the equations i posted flux equations. one of them is for a surface of a solid and the other is for a curve?
  7. T

    Solving a Complex Flux Integral Problem

    Homework Statement Homework Equations I know that flux is ∫∫F[r(t,s)]dotted[∂r/∂s x ∂r/∂t]dtds The Attempt at a Solution So I parameterized the equation y=x^2+z^2 as: x = s y = s^2 + t^2 z = t r(t,s) = [s, s^2+t^2, t] I take the partial derivative of r with respect to s and t and then...
  8. A

    Flux Density (Jy) to Luminosity when wavelength is involved

    Hi, I think my problem may be a little trivial however I have been stuck on it for quite some time. I have plots of flux density (Jy) versus wavelength in order to look at a particular forbidden line. I want to find the luminosity of the line, however as I am dealing with Jy [W/(m^2 Hz)] I do...
  9. A

    Transformer Calculations - determining turns/current/maximum flux

    The Question A single phase transformer has the following rating: 120 kVA, 2000 V/100 V, 60 Hz with 1000 primary turns. Determine: (A) the secondary number of turns (B) the rated currents on the primary and secondary (C) The maximum flux (D) given a maximum flux density of 0.25 T, the...
  10. D

    The model of electric flux in solids

    hi there! I have a bit stupid question: Imagine a solid metal cylinder. We put a . Explain to me please the exact model of the direct current electric flux of the particles. Is there a "skin effect" when a direct current is in action ?
  11. K

    Definitions for Magnetic flux and Faraday's Law

    I was wondering if my understanding on Magnetic flux and Faraday's law was correct or not, is this okay? Magnetic flux is the number of lines in a magnetic field (Φ) Magnetic field strength (B) is the number of magnetic field lines over a given area B = Φ/A Other names for magnetic field...
  12. J

    What is different in Solar Radio vs Radio Flux 10.7 cm?

    Referring to following links, I would like to know whether Solar Radio is equal to Radio Flux or not, it seems that it describes Solar Radio in different format. Are they monitoring the same objects? Does anyone have any suggestions on what the different is between them? Thanks in...
  13. C

    Flux Trapping Effect: Magnetic Suspension & Levitation

    Magnetic suspension and levitation is the caused by the flux trapping effect in superconductors.How does this flux get "trapped"? Another quick question- We link a magnet to a superconductor by bringing it very close to one ,until both of them start attracting and repelling. My question is...
  14. C

    Flux Trapping Effect: Magnetic Levitation & Suspension Explained

    Magnetic suspension and levitation is the caused by the flux trapping effect in superconductors.How does this flux get "trapped"? Another quick question- We link a magnet to a superconductor by bringing it very close to one ,until both of them start attracting and repelling. My question is...
  15. W

    Flux in different coordinate systems

    I have an electromagnetic field with a Poynting vector that has the following form in spherical coordinates: $$\bar{P}(R,\phi,\theta)=\frac{f(\phi,\theta)}{R^2}\bar{e}_{r}$$ The exact nature of f(\phi,\theta) is not known. Suppose I measure the flux of this vector field by a flat area...
  16. K

    A question on flux, and on field integration

    hey all, i've recently started studying electrostatics, and i have couple of question about things that i did not fully understand, and would very much appreciate if someone could set me straight. 1) how can a cube, with a single charge in the middle of it have a flux? don't the field lines...
  17. J

    What is the Nature of Solar Radio Flux?

    Referring to following link about Solar Radio Flux, I would like to know more about Solar Radio Flux, is Solar Radio Flux different from Electric Flux? What is the major difference in term of properties of their fluxs? Does anyone have any suggested materials on what Solar Radio Flux is about...
  18. R

    How to convert flux from counts to erg.

    Hello everyone. I am trying to translate the flux of a source observed by a telescope, in different units. In my case, I have the flux equal to counts/cm^2/sec in a given energy band (15-50 keV) and I want to translate this information in erg/cm^2/sec, in the same energy band Here you can...
  19. T

    Transformer, flux linkage and emf short question

    http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_s05_qp_4.pdfHomework Statement 6b Homework Equations flux linkage = BA B=F/iL The Attempt at a Solution from my understanding, if B=F/iL , if the current is zero...
  20. U

    How do I derive the particle flux for a cylindrical vessel?

    Homework Statement Consider a cylindrical vessel with cross-sectional area 1m^2 Derive the particle flux (1/4n\bar{v})Homework Equations I have the solid angle: \Omega = 2π(1-cosθ) The Attempt at a Solution I'm assuming that the solid angle represents the full area that the particles can...
  21. C

    Surface integral (Flux) with cylinder and plane intersections

    Homework Statement Evaluate the surface integral \int_{S} \int \vec{F} \cdot \vec{n}\,dSwith the vector field \vec{F⃗}=zx\vec{i}+xy\vec{j}+yz\vec{k} . S is the closed surface composed of a portion of the cylinder x^2 + y^2 = R^2 that lies in the first octant, and portions of the planes...
  22. U

    MHB Compute the downwards flux of F

    The work done so far https://www.dropbox.com/s/qmfidqot3nttlw5/phpQd8GGH.png https://www.dropbox.com/s/xn4t5m2aleopwy7/phpldZ0KX.png Is the answer correct...
  23. D

    Neutron flux in a finite medium

    Deaar all good morning I am very interested to the flux in a slab of extrapolated thickness a, containing distributed sources of neutron. A I have an example in which the source is given as s(x)=S(x+a/2) where S is a constant and x distance from the center of the slab. You mentioned in one...
  24. J

    Why Do Different Sources Show Varying Electric Flux Equations?

    Homework Statement Im starting to read about the electric flux and gauss's law. I am reading two books, Serway and Schaums electromagnetics. The weird thing is that I'm getting different equations for the electric flux Serway says that the Electric flux ψ is ∫E ds = 1/ε ∫ρ dv =...
  25. iVenky

    What exactly is Electric Flux Density?

    We define flux density as D= ε E right? or even ∇.D=ρ But I can't link the above with what is given in the wiki where they have used the symbol "phi" http://en.wikipedia.org/wiki/Electric_flux What is the difference between D and symbol "phi"? I would be really happy if you could...
  26. I

    EMF induced via change in magnetic flux vs. velocity in magnetic field

    Homework Statement (See attached diagram)--Note this problem was taken from Barron's SAT Physics Practice Test 1 #58 As the loop rotates, the induced voltage will be maximum at... a) 0 degrees and 90 degrees b) 0 degrees and 180 degrees c) 90 degrees and 270 degrees d) 180 degrees and 270...
  27. G

    What is the mass flux through a kidney?

    Homework Statement Water enters a kidney through a tube at 10 mL/min. It exits through a 6-mm-diameter tube at 20 mm/s.What is the rate of change of mass of water in the kidney? Homework Equations m=vpa q=va After conversions to meters V=.02 Q=.000167 A=(pi/4)*.006^2 = .0000282...
  28. bcrowell

    Speed of mass-energy flux, derived from stress-energy?

    The dominant energy condition is interpreted as meaning that no observer will see a flux of energy flowing at speeds greater than c. In this post I'm basically asking how to relate this concept of "speed of the energy flux" more precisely to the stress-energy tensor. If we start with dust...
  29. R

    Help find the flux through the surface

    Homework Statement Given a vector field A=(2x,-z^2,3xy), find the flux of A through a surface defined by ρ =2, 0<\phi<\pi/2, 0<z<1 Homework Equations ∇\bulletA? The Attempt at a Solution Can I use divergence method here? This is a closed surface correct? A cylindrical...
  30. R

    Flux through a cylindrical wedge surface

    Homework Statement If vector A=(2x,-z^2,3xy), find the flux of A through a surface defined by ρ =2, 0<\phi<\pi/2, 0<z<1 Homework Equations divA? The Attempt at a Solution Can I use divergence here? This is a closed surface correct? Is this is a cylindrical wedge? Also do I need to...
  31. K

    Flux of an infinite line of charge through a cylinder

    Homework Statement http://smartphysics.com/Content/Media/Images/EM/03/h3_lineD.png charge density 1 = .00029 C/m charge density 2 = -.00087 C/m h = .116 m a = .094 m a) What is the total flux Φ that now passes through the cylindrical surface of height h=.116 m? Enter a positive number if...
  32. B

    Using the Maxwell distribution laws to prove the collision flux equation

    I have for a while been trying to understand the setup of this equation in calculating the collision flux of a gas through a given rectangular surface of area A: Number of collisions in a time interval Δt is (\frac{N}{V})AΔt\int^{∞}_{0}v_{x}f(v_{x})dv_{x} where f(v_{x}) is the fraction of...
  33. B

    How Do You Calculate Electric Flux Through a Cube with a Central Charge?

    **I need Help calculating Electric Flux? Homework Statement "A 2.51 μC point charge is placed at the center of a cube with a volume of 7.27 m3. Calculate the electric flux through one side of the cube." Homework Equations Eflux = E*Surface Area The Attempt at a Solution I tried...
  34. S

    How Does Gauss' Law Apply to Infinite Charge Slabs?

    Homework Statement An infinite slab of uniform charge density ρ occupies the region -∞<x< ∞, -∞<y<∞, -d/2<z<d/2. Homework Equations Use Gauss' Law to calculate the electric field density for -∞<z<∞ The Attempt at a Solution D=εE. Using that, I just need to find D =...
  35. D

    Puzzled about direct current and charge (flux)

    This is a question that has kept me awake, trying to rationalise it: Current is rate-of-change-of-flux (or charge if you prefer, which is the same thing): i = dQ/dt Therefore, flux or charge is the time integral of the current. Q = ∫i dt Therefore, if you have a direct current, does...
  36. A

    Understanding the Flux Rule for Motional EMF?

    The flux rule for motional emf can be stated as: d\phi/dt = -\epsilon I have some questions regarding this. 1) Should I find this rule intuitive? And secondly a proof of this rule is given in my book, which I have attached. I don't really understand the idea of the proof - is the idea to...
  37. E

    The Electric Flux on all sides of a cube

    Homework Statement Homework Equations \phi = \vec{E} * A * d phi is the electric flux E is the Electric field from vector form A is the area and A = \pir^{2} d is the distance on the axis (x, y, or z) The Attempt at a Solution s1 = s3 = 0 *Since they are along the y-axis...
  38. 6

    Flux & Circulation Homework: Find Values & Prove Non-Zero Flux

    Homework Statement Let F(x,y) = ( P(x,y), Q(x,y)) be a vector field that is continuously differentiable along the closed smooth curve C : x2+y2 = 1. Moreover let -F(x,y) = F( -x, -y)≠ 0 and P(x,y) = -P(-x,y) and Q(x,y) = Q(-x,y). Determine all the possible values of the circulation...
  39. gluons

    Need help evaluating flux integral

    I have constructed a formula to represent the neutron flux from a disc emitter through an aperture. I have got it down to a double integral of a form that I can't see how to evaluate. Mathematica crashes on this and I am not ready yet to give up and go to numerical solution. Does anyone know a...
  40. S

    Flux in Through/ Out of Caps Purcell

    "Flux in Through/ Out of Caps" Purcell Homework Statement I'm working problem 5.11 in Purcell's E&M book. It's about relativistic particles, and the eventual condition about angles at which the E-field lines are directed. The ultimate goal is to prove that tan(\varphi)=\gammatan(\theta)...
  41. D

    Lumens and photon flux density

    Is there a simple way of calculating photon flux density from the lumens produced by a fluorescent tube?
  42. M

    Magnitude of magnetic flux of a solenoid using Biot-Savart law

    Homework Statement A 10 cm long, 1 cm diameter solenoid contains 500 turns of wire. A current that varies as I = 5Sin(100πt) Amps flows through the solenoid wire. Calculate the magnitude of the magnetic flux at the centre of the solenoid as a function of time using equation (1). Compare this...
  43. T

    Energy stored in coil with given relationship between current and flux

    Homework Statement The relationship between the current in an N-turn coil and the flux created by it is given as: \Phi = \frac{ai}{b+ci} Determine the energy stored in the coil when the current varies from 0 to I. Homework Equations W = N \int{i d\Phi} The Attempt at a...
  44. G

    Flux, how to find n (normal) and derivation of formula?

    Homework Statement Find the flux of the following fields: F_1 = xi + yj F_2 = -yi + xj across the following curve: The circle r(t) = (cost) i + (sint) j t is from [0,2pi] Homework Equations Flux = ∫F dot n ds = ∫M dy - N dx The Attempt at a Solution For F_1 I got: M = x =...
  45. L

    Calculating Stellar radius from bolometric flux

    Homework Statement The monochromatic flux emitted from unit surface area of a black body is given by F_{\lambda}(T) = \frac{2h\pi c^{2}}{\lambda^{5}} \frac{1}{exp(hc/\lambda KT)-1} Wm^{-2}m^{-1} If the distance to star X is 620 parsecs, calculate: (a) the radius of star X, in...
  46. T

    How to find magnetic flux density at center and ends of solenoid

    Homework Statement A solenoid has a radius of 2mm and a length of 1.2cm. If the # of turns per unit length is 200 and the current is 12A, calculate the magnetic flux density at a) the center and b) the ends of the solenoid Homework Equations The biot-savart law: \vec{B} = \frac{\mu_0}{4...
  47. R

    Are My Flux Calculations for Toroids and Solenoids Correct?

    This is more a theoretical question than a practical one. Basically I want to know if the formulas I arrive for the flux of a Toroid and a Solenoid are correct Leaving aside the integration part this is the basic formula for the flux \phi = BNA B = magnetic field N = number of turns of...
  48. O

    Electric field, magnetic flux , potetial difference

    Homework Statement As shown in the figure below, potential difference V exists between two parallel plates(a,b) that have a small hole. Uniform electric field E and magnetic flux density B exist in the region above the plates, and are perpendicular to each other. The directionof E is parallel...
  49. P

    Surface flux through a single finite element

    Hi, I'm facing a real-life problem and I don't what specific mathematics topic it's related to. Homework Statement I know the value of the components of a vector field in three points of space and I have to find the flux of this vector field through the surface defined by those...
  50. T

    How does wireless power transfer produce magnetic flux?

    From what I learned, for an electric current to be induced in a wire, there must be a magnetic flux. On youtube, there are lots of videos showing wireless power transfer to a lightbulb or LED. However, the light is constant. How is the magnetic flux changing in such a setup?
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