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. electr

    Estimate the local heat transfer flux

    Homework Statement Liquid ammonia is heated as it flows at a mean velocity of 2 m s–1 through a circular pipe. The pipe, which has an internal diameter of 75 mm, is at a uniform temperature of 27°C, and the ammonia at a section 1.2 m from the inlet to the pipe has a temperature of –23°C. Use...
  2. Cocoleia

    Magnetic flux, current and magnetic field confusion

    1. The problem statement Relevant equations: I am confused. When dealing with Ampères law: dl is supposed to be the length element? Like when we have Gauss' law for electric fields and we use a circular Gaussian surface, we have E(4πr^2)=Qenclosed/ε So in this case, when we have a circular...
  3. S

    Magnetic flux - magnitude of the change

    Homework Statement A 200-loop coil of cross sectional area 8.5 cm2 lies in the plane of the page. An external magnetic field of 0.060 T is directed out of the plane of the page. The external field decreases to 0.020 T in 12 milliseconds. (a) What is the magnitude of the change in the external...
  4. D

    Magnetic flux through a rectangular loop inside a wire

    Homework Statement Homework Equations Magnetic flux = integral(B dot dA) line integral(B dot ds) = (u_o)(i_enc) (Ampere's Law) The Attempt at a Solution I can't see how Ampere's law applies because all of the magnetic field vectors along the loop will be perpendicular to that stretch of...
  5. L

    Magnetic flux between 2 parallel wires

    Homework Statement Consider two long parallel wires each of radius a with a separation distance d between them. They carry current I in opposite directions. Calculate the magnetic flux through a section of length l, ignoring magnetic field inside the wires. My confusion lies in trying to...
  6. S

    Magnetic flux through a loop at two orientations

    Homework Statement A circular loop of radius 0.10 m is rotating in a uniform external magnetic field of 0.20 T. Find the magnetic flux through the loop due to the external field when the plane of the loop and the magnetic field vector are (a) parallel. (b) perpendicular.Homework Equations...
  7. P

    Building speakers, induction and induced current

    i made a speaker from a cup, a coil of wire and a magnet. I hooked up both of the ends of the wire to a headphone jack and it works. Albeit very low sound, but it works. Can you point me in the direction of some equations that will show me the most influential factors on how to make it louder...
  8. F

    Difference in formulas of magnetic force and magnetic flux

    The magnetic force is defined as ## \rm F_e = Bqvsin\theta## and the magentic flux is defined as## \rm \phi = BAcos\theta## My question is since we are multiplying the two vectors, why is ##sin\theta## used in one equation and ##cos\theta## in second given that ##\theta## is the angle between...
  9. G

    Weber & Flux Density: Learn How 1 Wb = 10^8 Lines of Magnetic Flux

    Hi, Eqn B = phi/A For flux density so 1T = 1Wb/m^2 Often wondered about a Weber and found on a site that 1 Wb is 1 x 10^8 lines of magnetic flux! Does this sound right that an exact amount of flux lines represents 1weber? I always thought that the concept of webers was a relative idea and not...
  10. Y

    Calculating magnetic flux of a rod

    Homework Statement B = 0.02T L = 40 cm w = 10 rad/s a: Electromotive force between O and C = ? b: If electromotive force is the same - so what is the velocity? I found 2 ways of solution. See "3. The Attempt at a Solution "Homework Equations φ = BA ε = -dφ(t)/dt The Attempt at a Solution So...
  11. W

    A question on E Flux and Fields

    Homework Statement 1. The field for an infinite charged sheet is found to be σ/2ε0. If we place 2 infinite sheets of opposite charge above one another, we say that the field in between the sheets is σ/ε0 due to the superposition of individual fields. Why can't we say the same for a situation...
  12. T

    Flux and Induced EMF vs displacement graphs

    Homework Statement A small coil of wire is situated in a non-uniform magnetic field. The coil consists of 40 turns of wire and moves with a constant speed in a straight line. The coil has displacement x from a fixed point P. The variation with x of the magnetic flux in the coil is shown in the...
  13. Amy

    Flux of high charge positive ions, how?

    I need a flux of highly positive ions, at least penta-valent ions (5+ or more, 6+, 7+, ...); there are ion sources that can generate a proton flux, but I need 5+ ions; do you know how I can do that?
  14. P

    Does the first maxwell equation apply only....

    For static electric fields? does it apply also for a generic electric field? Let's say, moving charges inside a closed surface? If there are charges accelerating in a closed surface a part of the electric field is due to the charges, and a a part is due to the fact that the charges acceleration...
  15. M

    X-ray tube flux and my experimental test setup

    Hi everyone! I'm starting to work with a mini X-ray tube provided by Amptek. I want to use it to calculate the efficiency of a detector I'm going to use latter, so knowing the total flux the tube emmits and measuring the flux the detector receives, that should be enough (both data normalized to...
  16. X

    Why does induction in a loop depend on the contained flux?

    Hiya, I'm struggling to find/figure out some kind of intuitive explanation why it is the changing flux of the contained area that matters for Faraday's law of induction. It appears odd to me that it is the change of flux through the contained area that matters, rather than the flux that goes...
  17. I

    Magnetic Flux Through a Square Loop

    Homework Statement A loop of wire in the form of a square 1.50 m on each side, its plane makes an angle of 40.0° with a uniform magnetic field of 0.95 T. What is the magnetic flux through the loop? Homework Equations Φ = BAcosθ A = s^2 The Attempt at a Solution I found the area of the square...
  18. J

    Elementary question on Electric flux units

    The net flux over a closed surface is: Flux = The surface integral of the field E = charge / permitivity in space (Gauss law) The permitivity in space is: 8.85 10-12 Coulombs2/N m 2 So I understand the units of Flux are: Newton meter2/Coulombs Is this correct? I don't understand why in a...
  19. G

    Comparing inductance and capacitance: Analogy to charge

    Hi. Inductance and capacitance have many analogies, both conceptually and formally. A capacitor connected to a voltage source carries the charge ##Q=C\cdot V##. The analogous equation for inductance is ##n\cdot \Phi=L\cdot I##. Charge is physical, it's proportional to the number of excess...
  20. B

    Flux Density, B, of a Cylindrical Magent

    Hi, I'm trying to calculate the flux density of a magnet, I can get all but one of the values needed to calculate it. Does anyone know how/where to get the z(distance from a pole face on the symmetrical axis) value?
  21. G

    Magnetic flux and current directions of transformer

    Hello. Let's take a transformer picture first. The basic equation explaining how the transformer work is the equation of Faraday's law of induction. \begin{array}{*{20}{c}} {{V_P} = - {N_P}\frac{{d{{\rm{\Phi }}_B}}}{{dt}}\;\;\;\;\left( 1 \right).}\\ {{V_S} = - {N_S}\frac{{d{{\rm{\Phi...
  22. S

    Working out heat transfer flux in a pipe

    1. Question 2. The attempt at a solution Now I'm not sure where to go next? Do I work out the local heat transfer coefficient at 1.2m or just the heat transfer coefficient? Using h = Nu × k/x or h = Nu × k/d Thanks, Sam.
  23. G

    Transformer equation: Using Faraday's law "the wrong way"?

    Hi. All derivations of the (ideal) transformer equation ##\frac{U_p}{U_s}=\frac{n_p}{n_s}## use Faraday's law of induction $$U=-n\cdot \frac{d\Phi}{dt}$$ for primary and secondary and equate the change of flux ##\frac{d\Phi}{dt}##. Until now, in my textbooks it was always like this: Electrical...
  24. C

    Electric Flux and Electric Flux Density

    Homework Statement Hi, So I'm doing a electromagnetics course and we've been given equations for electric flux and electric flux density but I can't seem to find any sort of intuitive explanation for these. In my lecture notes, the electric flux density is introduced first as vector D and...
  25. S

    I Understanding the Concept of Momentum Flux in Stress: Explained and Demystified

    I'm trtying to get a better understanding of the spatial part of the energy-momentum tensor, and although similar questions have been asked here, I think the point I do not fully grasp has not been covered so far. The stress tensor can be considered as "momentum flux density" tensor. If I...
  26. N

    Magnetic flux and how to manipulate it discussion anyone?

    Good day all, I am looking to discuss how to manipulate the magnetic flux of a coil. I unfortunately lack the math skills to calculate what I actually need to build for my project. I have been coop up in my garage trying to physically solve the problem but I am running out of time and money for...
  27. A

    Flux Through a Gaussian Surface

    Homework Statement A metal sphere of radius a is surrounded by a metal shell of inner radius b and outer radius R, as shown in the diagram below. The flux through a spherical Gaussian surface located between a and b is 1.20Q/εo and the flux through a spherical Gaussian surface just outside R is...
  28. J

    Net electric flux through a Gaussian cube

    Homework Statement An electric field given by https://edugen.wileyplus.com/edugen/shared/assignment/test/session.quest2560893entrance1_N10030.mml?size=14&ver=1486488694211 =...
  29. jlmccart03

    Electric Flux through half a cylinder

    Homework Statement In (Figure 1) take the half-cylinder's radius and length to be 3.4 cm and 15 cm, respectively. If the electric field has magnitude 5.3 kN/C, find the flux through the open half-cylinder. The surface here is the right half of the surface of a full cylinder. The surface does...
  30. jlmccart03

    Electric Flux confusion and help

    Homework Statement I have three questions spanning three different situations, but each deal with the single concept of electric flux. Problem 1: Write an expression for the net electric flux through the entire surface in terms of the area vectors and the electric field E. Problem 2...
  31. jlmccart03

    Magnitude of electric flux through a sphere?

    ****EDIT****: I had improper significant figures. It was the correct number. 1. Homework Statement The electric field on the surface of a 6.0 cm -diameter sphere is perpendicular to the surface of the sphere and has magnitude 52 kN/C . What is the magnitude of the electric flux through the...
  32. W

    Understanding Electric Fields and Flux in Charged Objects

    Homework Statement Not so much of homework questions but more to do with clarifying concepts: 1. How do i assess whether or not field lines emitted by charged objects (i.e uniformly charged cube) are both perpendicular to their surfaces uniform? This is in relation to taking the E of ∮φ = EdA...
  33. A

    Magnetic flux through a triangular loop?

    Homework Statement Determine the mutual inductance between a very long, straight wire and a conducting equilateral triangular loop Homework Equations I know how to do it but I'm stuck at the step of finding the total inductance through the triange. The Attempt at a Solution we know that the...
  34. J

    I Inhibit repulsion between two like poles

    Please excuse the lay terms that will follow. I have been doing some reading on "magnetic shielding" and have come across alloys such as MuMetal which have high permeability and so can block interaction between two magnets. My question; Is this inhibition of interaction between the two...
  35. A

    What Surface Does ds Represent in Calculating Magnetic Flux Through a Toroid?

    Homework Statement The general method to find the total magnetic flux through an object is found by: Φ =∫B*ds (dot product) what is the ds over which we take the integral on?? what surface is it?, is it the surface over which the magnetic flux enters? Homework Equations Φ =∫B*ds (dot product)...
  36. I

    How to convert MNCP F4 tally to neutron flux (n/cm2s).

    how to convert MNCP F4 tally to neutron flux (n/cm2s). and how to calculate average neutron produced per fission from given nuclear fuel mixture (eg. mixture of 80.8% enriched U-235 and U-238 as fuel material).
  37. enerieire

    How Is the Flux of Poynting's Vector Calculated Through a Surface?

    I have some problems in calculating the flux of Poynting's vector through a surface. I have that: S=c/4π⋅H^2⋅n (S: Poynting's vector, n: versor of the direction of the propagation of the em wave) H=1/cR A' but: A=(1/cR) d'; A'=(1/cR) d'' ==> H= (1/cR)^2 d''...
  38. J

    Is there energy associated with flux pinning?

    This is probably a very naive question, but I am trying to wrap my head around the concept of flux pinning (quantum locking). For all intents and purposes, it appears as if a superconductor suspended above a magnetic field is defying gravity. I understand that there is no work being done (as...
  39. Z

    Heat flux analysis with transient heat conduction

    Homework Statement I have one dimensional heating system. In the center is heating source which is heating two PVC elements located on both sides of the heating source. Heat distribution in other dimensions is negligible because of insulation. Thickness of one PVC element is 0,051 m and surface...
  40. C

    Flux through rim created by moving circuit and induced EMF

    In Purcell- Electricty and Magnetism book, in the chapter on electromagnetic induction, I found the following explanation regarding the magnetic flux through a circuit of area ##S##. Consider the circuit in figure, moving in a time ##dt## in a magnetic field ##B##, constant in time (but not...
  41. texasnano

    A Does increasing photon flux density increase attenuation?

    follow up from responses in old thread. https://www.physicsforums.com/threads/why-does-attenuation-coefficient-decrease-with-increased-energy.569981/ I have seen in my experiment using a saline media ( some oxygen bubbles) that an increase in Incident PFD is showing an slight increase in the...
  42. A

    Backing-out luminosity togo from lumens to radiant flux in W

    Hi. Has anyone already done the work to back out the standard luminosity function so I can go from lumens at a particular wavelength to radiant flux in Watts? I have visible LED spec sheets with optical characteristics in lumens and I want to calculate the outputs in W. My NIR LED has specs in...
  43. A

    Drawing flux and induced EMF graphs - Faraday's/Lenz's law

    I would really appreciate some clarification about how to draw graphs showing changing flux and induced EMF. I understand that there needs to be a 90 degree phase difference as the EMF is a maximum when the flux has the greatest rate of change. However, our exam board says that the EMF can be...
  44. L

    Optical detector sensitivity at low and medium flux

    Dear all, This is my first post and I'm not sure if it's the right place to ask so don't hesitate to advise if necessary. I would like to know if it's possible that an optical detector (the complete system including sensor and front-end electronics) has a better sensitivity at medium flux than...
  45. E

    Determine flux in air gap (Magnetic Core)

    1. Homework Statement As shown above Homework Equations *Not too sure if they are relevant. Pretty sure there's more. We have textbooks from the library as references but we still can't quite figure it out :/ Φ = BcAc = BgAg B = Φ/Ac = (Ni/R)/Ac R = lc/(Ac.μ) The Attempt at a Solution...
  46. E

    How Is Scattered Flux Density Measured from a Ruby Laser in the Atmosphere?

    Homework Statement [/B] An unpolarized ruby laser operated at 0.7 μm is projected vertically into a clear sky to investigate the density of the atmosphere. A detector located 10 km from the base of the laser is used to receive the flux density scattered from the laser beam by air molecules...
  47. T

    Find magnetic flux density B circulation in closed contour

    Homework Statement Find magnetic flux density B circulation in closed contour. The countour consists of square with a perimeter of 4b. It includes a square conductor with a perimeter of 4a. A homogenic current flows through a conductor with a current density of j. Homework Equations...
  48. F

    Significance of magnetic flux between wires

    Homework Statement Two wires are laid side by side and carry equal currents in opposite directions. Explain why the total magnetic flux density due to the current in the wires is negligible 2. The attempt at a solution I know that having a different direction for the current results in...
  49. A

    What is the Magnetic Flux through a Loop with Opposite Magnetic Fields?

    Homework Statement Homework Equations Flux = DeltaB * Area The Attempt at a Solution : Since the magnetic fields are going in opposite directions through the loop, I assumed that they would have different signs, so I chose 2.0 T to be positive and 1.0 to be negative, so when calculating the...
  50. E

    Calculating Local Heat Flux in a Pipe: Is h = Nu*(k/x) the Correct Formula?

    I am a little unsure how to get started with a homework question. Essentially, I have to calculate the local heat flux at a distance 1.2m (x) along a pipe. I have the fluid's properties and have calculated the Reynolds number, for which I've determined the flow to be turbulent and therefore do...
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