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. Anakrystine

    Magnetic flux. Dont know where to start

    Homework Statement A circular area with a radius of 7.90cm lies in the x-y plane. A. What is the magnitude of the magnetic flux through this circle due to a uniform magnetic field B = 0.223T that points in the +z direction? B.What is the magnitude of the magnetic flux through this circle due to...
  2. 5

    Dimensional Analysis of Flux Equation for cross filtration

    Homework Statement The following equation is presented in my textbook, with very little context and J is simply described as the "trans-membrane fluid flux, which can be modeled by using Darcy’s law." Typically in this bioseparations class, when we discuss permeate flux, it is a unit volume...
  3. H

    Net flux through a cylinder from a point charge

    Homework Statement My book demonstrates how a uniform electric field through a box generates a net flux of zero. I was wondering if the same would happen from a point charge outside of the cylinder on one end instead of a uniform electric field. Homework Equations Flux = E⋅A The Attempt at a...
  4. LunaFly

    Flux of Circuit made from Metal Bar on Parallel Rails

    Homework Statement [/B] A simple model of a railgun is a metal bar which runs on two long parallel rails. The two rails are connected to a charged capacitor with capacitance C and a resistor with resistance R. After charging, the capacitor can discharge through the circuit. You may assume that...
  5. B

    Stacked magnets with air gaps and the effect on magnetic flux

    I wasn't sure where to put this so mods feel free to move, So this is a problem I'm trying to solve for a masters project and simplified it is this; I essentially have a stack of magnets all separated by 4mm each magnet is identical and produces a magnetic flux of 17.5 gauss at its centre (all...
  6. 3

    Calculating magnetic flux density using Biot-Savart law.

    Hello, all. I have been working on the following problem and was wondering if someone could check my work and provide some valuable input: Here is my work: What do you guys think about my approach to this problem?
  7. 3

    Charge passing through a magnetic field of uniform magnetic flux density

    My reasoning: The magnetic force on charge q is Fm = qv x B B does not change |v|. Therefore, |Fm| is constant at time t > 0 and Fm is always perpendicular to the direction of movement of charge q. Fm behaves as a centripetal force, and thus the charge moves along the circumference of a...
  8. C

    Flux distribution on AC machines

    It is a cylindrical ac machine. If we want to produce a sinusoidal voltage, we need B (magnetic density) to vary sinusoidally. To get B vary sinusoidally, we need to get H(magnetic intensity) to vary sinusoidally. To get H vary sinusoidal, the best way is to vary the numbers in the air gap...
  9. Battlemage!

    Current induced by magnet: maximize change in flux wrt time?

    I'm messing around with Faraday's Law of Induction, and I will be using two magnets attached either side to a small bar inside two coils of copper wire, which I spin to induce a current. The design is basically this: http://amasci.com/amateur/coilgen.html My question is, what shape for the...
  10. S

    Clarifying the notion of Flux Linkage

    Hello! Im having some trouble really understanding this concept. I'll summarize my difficulty in 2 situations that I struggle with: 1) Coil: The inductance of a coil with N turns is known to be proportional to N2. My question is why is that true? I know that the H-field (and therefore the...
  11. bananabandana

    Calculating Flux through Ellipsoid

    Homework Statement Let ## E ## be the ellipsoid: $$ \frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}+z^{2}=1 $$ Let ## S ## be the part of the surface of ## E ## defined by: $$ 0 \leq x \leq 1, \ 0 \leq y \leq 1, \ z > 0 $$ Let F be the vector field defined by $$ F=(-y,x,0)$$ A) Explain why ##...
  12. V

    Total radiant flux measurement of an LED with an optometer

    Measuring the total radiant flux with an optometer of SFH 4550 LED from osram I'm getting ~70mW, If I place 5mm long rubber hose around the led (top 2,5mm of the led is free), the power is reduced to 50-40mW. This does not make sens to me, the led has a half angle of ±3° and emits nothing to...
  13. T

    Flux Direction effect on Saturation, Quick Question

    Hi, If you've got an arbitary magnetic Flux1 and Flux2, traveling in the same or opposite directions, through a core, it doesn't matter with regards to the point on the saturation curve does it? Opposing or in the same direction it'll still be at the same point on the mag curve won't it?Thanks...
  14. V

    LED's classes of radinat intensity and total radiant flux

    I found that for some LED's manufacturers specify groups/classes of radinat intensity in their datasheets. For example SFH 4258 from Osram http://www.osram-os.com/Graphics/XPic0/00101891_0.pdf/SFH%204258,%20Lead%20%28Pb%29%20Free%20Product%20-%20RoHS%20Compliant.pdf has four groups, going from...
  15. J

    Why does speed of DC motor increase when flux is reduced?

    I understand that from KVL e = v -IaRa e=k(flux)speed speed=(constant)*(V-IaRa)/flux But physically what causes the speed to increase? What force causes the rotor to accelerate? In fact physically, the rotor is moving because of field flux interacting with armature current's flux. So...
  16. B

    Neutron diffusion around thin absorber

    Homework Statement Mono-energetic sources of neutrons emitting S neutrons/cm^3 sec are distributed uniformly throughout an infinite material (characterized by a macroscopic absorption cross section Σa and a diffusion coefficient D). An infinite sheet of very thin absorber, of thickness t and...
  17. Curiosity 1

    Electric Field of Line/wire Charge (E flux through Gs)

    Hi. Consider the cylindrical Gaussian surface (Gs) shown in the following picture: Using Gauss's law, ∫ E ⋅ dA= E ∫ dA = Q/ ε E 2 π r L = λ L / ε E= λ /(2 π r ε) Is this true? I have a feeling like this is wrong. We have considered that there is only ONE...
  18. B

    Help me understand magnetic flux linkage

    Magnetic flux linkage = BAN B=magnetic field strength per unit area A=Area of conductor moved through the magnetic field N=Number of coils I don't understand when my physics textbook says the area of a single coil of wire moved through the magnetic field is π×radius of coil^2 as most of the...
  19. R

    Flux through a Disk: What's Wrong with My Method?

    Homework Statement According to my textbook, the electric flux through a disk of radius R situated at a height d from the xy plane is given by: ##2 \pi k_0 Q [1- \frac{d}{\sqrt{R^2+d^2}}]## Where ##k_0 = \frac{1}{4\pi \epsilon_0}## I'm having some difficulty obtaining this answer. Homework...
  20. H

    Calculate the electric flux

    Homework Statement The Earth possesses an electric field of (average) magnitude 150 N/C near its surface. The field points radially inward. Calculate the net electric flux outward through a spherical surface surrounding, and just beyond, the Earth's surface. Homework Equations Flux =...
  21. A

    Why does electric flux have 'cos θ' in its formula?

    Why does electric flux have 'cos θ' in its formula??
  22. patrickbotros

    Why does a Charge Outside a Surface Produce No Net Flux?

    My textbook says "the net flux is zero through a closed surface that does not contain any net charge," and justifies it by saying that everything flowing in has an equal thing flowing out. This makes ABSOLUTELY NO sense to me.
  23. S

    Why is the flux through the top of a cylinder zero?

    This is example 27.2 in my textbook. I have the answer, but it doesn't make sense to me. I understand that if electric field is tangent to the surface at all points than flux is zero. Why, though, does my textbook assume that the ends of the cylinder don't have field lines extending upwards and...
  24. Seydlitz

    Deriving Ideal Gas using Molecular Flux Equation

    So basically I was wondering whether it's possible to get the expression of ideal gas using molecular flux equation which is ##\phi = \frac{1}{4}\bar{v}n##. The derivation should be straightforward. I need to get the expression of pressure. Because the flux by definition already gives the rate...
  25. E

    Life expectancy of Aqueous Flux going LowZ

    Looking for any life expectancy data for water soluble flux going low Z. How long it takes for conductive material to migrate and cause low impedance bridges at any humidity or temperature.
  26. M

    Physical significance of Volumetric Flux

    Homework Statement I am just a little bit confused. I have a question that is asking me to explain what the physical significance of volumetric flux is. Homework Equations I am not sure that this problem requires any equations! The Attempt at a Solution I know that the flux corresponds to...
  27. P

    Heat flux through wall question

    Homework Statement I was given this question. The wall of a building is constructed of face brick (10cm thick) and concrete block (50 cm thick) with an air filled cavity (5cm thick). The interior and exterior convection coefficients are 8.3 W.m^-2.K^_1 and 35W.m^-2.K^_1 respectively. The...
  28. B

    Outward Flux Through Cylinder

    Homework Statement Calculate the outward flux of F = 3z\mathbf{e_{\rho}} + cos(\phi)\mathbf{e_{\phi}} + 2z\mathbf{e_{z}} through the base of a cylinder centered at the origin with radius \mathrm{R} and height \mathrm{2H}. Homework EquationsThe Attempt at a Solution I am unsure of how to tell...
  29. Salvador

    Flux diode, magnetic semiconductors

    So I was reading about magnetic semiconductors and I got confused so can you please clarify I will ask a question that is made up of two parts. Magnetic semiconductors are ... a) devices that alter or switch on/off electric current flow depending on the magnetic field strength etc applied OR b)...
  30. AdityaDev

    Diamagnetism and orbital magnetic moment

    For diamagnetic materials, when an external magnetic field is applied, the electrons having orbital magnetic moment in opposite directions spped up. how does this happen? The direction of magnetic momwnt is given by right hand thum rule. If there is an electron revolving in anticlockwise...
  31. Z

    Is there any refined experimental result on flux quantum?

    So far I have only found the initial papers of Deaver, Bascom; Fairbank, William and of Doll, R.; Näbauer, M. Is there any later and refined similar experiment result?
  32. E

    Graphing the flux density between two line charges in matlab

    Homework Statement I am trying to graph the flux density field between two infinite line charges located at y = 1 and y = -1 Homework Equations I am trying to do it using the equation for a line charge that I got from lecture notes. The above equation is derived from this: Here is the...
  33. M

    Finding magnetic flux density from magnetization vector

    Homework Statement A long cylinder of radius a with magnetization vector M=M_0*(r/a)^2*a_φ. Find the magnetic flux density inside and outside the cylinder. Homework Equations J_m=∇×M J_ms=M×a_n[/B] A=(μ_0/4*π)*(∫(J_m/R)dv+∫(J_ms/R)ds) B=∇×A The Attempt at a Solution Basicly what I thought...
  34. P

    Electric flux through a sphere

    Homework Statement An uncharged nonconductive hollow sphere of radius 12.0 cm surrounds a 11.0 µC charge located at the origin of a cartesian coordinate system. A drill with a radius of 1.00 mm is aligned along the z axis, and a hole is drilled in the sphere. Calculate the electric flux through...
  35. G

    Neutron Flux in ITER: Benefits & Containment Challenges

    I was reading that the ITER will take advantage of the energetic neutron flux by using them and lithium 6 to breed tritium for more fuel, and to use multiple heat exchangers to grab their energy. And just to make sure that I'm reading it right, the main problem with the neutrons will be their...
  36. A

    Heating a metallic rod from one end by continuous heat flux

    What is the solution of heat transfer equation when there is continuous heating ( flux of energy) to one end of a metal rod? what will be the temperature profile before reaching the steady state? when I try the boundary condition where one end (x=0) is kept at T1, I got the general solution of...
  37. V

    Flux through various Gauss' surfaces

    Homework Statement I have uploaded a file that shows the question.[/B]Homework Equations I believe the only relevant equation is: flux = Q(enclosed)/E(knot)[/B]The Attempt at a Solution Well I have some questions first. The problem statement says that the sphere on the left has a net...
  38. V

    Calculating Electric Field Flux for Non-Uniform Fields: Gaussian Cubes Example

    Homework Statement 6 Gaussian cubes are shown below. The surfaces are located within space containing non-uniform electric fields. The electric fields are produced by charge distributions located outside the cubes (no charges in the cubes). Given for each case is the side length for the cube...
  39. C

    Find Electric Flux Through Surface 2

    Homework Statement The drawing shows an edge-on view of two planar surfaces that intersect and are mutually perpendicular. Surface (1) has an area of 2.20 m², while surface (2) has an area of 3.90 m². The electric field in the drawing is uniform and has a magnitude of 200 N/C. Find the...
  40. S

    Total Magnetic Flux Density Law Problem

    We know Total Magnetic Flux B = B_0 + B_m Where, B_0 is the external field and B_m is the field inside a material. Now, we get, B = B_0 + μ_0*M (M is the magnetization) My question is - Do I always have to use μ_0 ? If yes then Why? The material isn't free space, is it?& also B =...
  41. T

    Electric flux through cubical box

    Homework Statement If the electric field is constant in direction (horizontal in the x direction) but its magnitude decreases from E1 to E2, determine the flux through a cubical box of side length L if four of the sides of the box are parallel to the field. Homework Equations ∫EdA = flux The...
  42. B

    Finding flux through ellipsoid in Cylindrical Coordinates

    Homework Statement Using Cylindrical coordinates, find the total flux through the surface of the ellipsoid defined by x2 + y2 + ¼z2 = 1 due to an electric field E = xx + yy + zz (bold denoting vectors | x,y,z being the unit vectors) Calculate ∇⋅E and then confirm the Gauss's Law Homework...
  43. T

    Induction and flux linkage clarification

    So if you have a single inductor then I assume that there is no flux linkage and that L = flux*N / i = L11 and so that flux is total leakage flux. If you have two inductors then the flux leakage is any flux that isn't flux linkage (the self flux is flux leakage). (flux21 is the flux in 2 from...
  44. L

    Question on Surface Integral and Flux

    Homework Statement I have a coordinate system, (x,y,z). There is a uniform-magnetic-field of 2.0 T that exists along the direction of the y-axis. There is a rectangular plane bounded by the points (3,0,0),(0,1,0),(0,1,1),(3,0,1). Calculate how much flux is traveling through the rectangular...
  45. 2

    Model of how temperature depends on latitude?

    Homework Statement I was asked to 'Use a very simple model to find how the Earth’s temperature should vary with latitude.' Homework EquationsThe Attempt at a Solution I was thinking about flux and how this should be proportional to the temperature. So I first thought about the area that is...
  46. J

    Is an induced emf always produced by a change in flux?

    Faradays law tells us that a change in flux induces an emf. Now consider the phenomenon of motional emf. It is observed across the ends of an open conductor (ie one which is not in a circuit). It is always discussed in connection to faradays law. Where is the change in flux in the case of a...
  47. M

    Why Does Rearranging an Inductor Yield Different Magnetic Fields?

    I found two ways to solve this problem, but I get two different solutions, it's confusing because I can't see the flaw in wrong solution. 1. Homework Statement Long cylindrical inductor of diameter D1 and inductance L1 is connected to battery and creates magnetic field B1. Inductor is then...
  48. M

    Flux Through a Non-Concentric Sphere

    Homework Statement Assume I want to calculate the electric flux through a spherical surface centred at point P with radius R which contains a point charge Q, that is not concentric with the spherical surface. Here, I can no longer assume that ∫∫sEdA = E.A, and I have to calculate the value of...
  49. N

    Calculating Neutron Flux using SN Method

    when we calculate the neutron flux in finite medium using sn method for steady state neutron transport equation, it gives us some numbers up to 1. I am sure its not the real flux, can someone explain how we can calculte the real flux using sn method.
  50. Y

    Why is Magnetic Flux Important in Understanding Induction?

    can someone tell me , why must the magnetic flux be taken into account instead of magnetic field ?? thanks...
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