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. W

    Flux through the Surface of the Plane

    Homework Statement Find the upward flux of F = <x + z, y + z, 5 - x - y>, through the surface of the plane 4x + 2y + z = 8 in the first octant.Homework Equations ∫∫(-P(∂f/∂x) - Q(∂f/∂y) + R)dA where the vector F(x,y) = <P, Q, R>, dA = dxdy and where z = f(x,y) <-- f(x,y) is the function that...
  2. S

    Flux at Earth's surface and Poynting vector

    (On phone typing this, so preset subheadings haven't shown) My first question asks me to use the Poynting vector, N, to calculate the average flux of radiation, knowing that the electric field of sunlight arriving at the surface of the Earth is 500Vm^-1 I use that the average flux of...
  3. A

    Calculation of ion flux across potential barrier

    Hello! As far as I know, the Eyring equation is used to calculate the speed of a reaction: k=\frac{{k}_{b}}{h} {e}^{\frac{-\Delta G}{RT}} In my course the teacher used this formula to calculate the flux of a species of ions across a barrier of potential, but I didn't understand very...
  4. R

    Calculating EMF and flux rule

    Hi, I'm currently reading griffiths and I'm a little bit confused in how it calculates emf. EMF is initially introduced as a path integral of force/unit charge around a closed loop. This makes sense, but then he presents us with an example problem (ex 7.4) Basically, a circuit resistor is...
  5. R

    Removal of Polynomials From Raw Aperture Flux Time Series?

    Hello! This is my first post so forgive any errors of decorum. :o) I am a student working toward a degree in astrophysics but I'd like to jump a few years ahead when it comes to the study of exoplanets. While examining some data about the new discovery of Kepler-22b, I noticed a plotted data...
  6. S

    Finding Charge From Changing Magnetic Flux

    Homework Statement In the figure, a flexible square loop 0.700 m on a side is made of wire of resistance 0.600 Ω. A magnetic field with magnitude 1.70 T is directed onto the plane of the loop. A student crushes the wires together forming a loop of zero area in 0.350 s. Find the total amount of...
  7. N

    Need help finding flux across a surface

    Homework Statement Find the upward flux across the surface z = x of the vector field F=(y,-x,0). Homework Equations ∫∫(F\bulletn)ds The Attempt at a Solution I know what to do once I parametrize z = x but I am stuck on the parametrization. Would it just be: r(x,y) = (zi + j + xk) ?
  8. W

    Flux of a Paraboloid without Parametrization

    Homework Statement Find the outward flux of F = <x + z, y + z, xy> through the surface of the paraboloid z = x^2 + y^2, 0 ≤ z ≤ 4, including its top disk. Homework Equations double integral (-P(∂f/∂x) - Q(∂f/∂y) + R)dA where the vector F(x,y) = <P, Q, R> and where z = f(x,y) <-- f(x,y) is the...
  9. M

    [Multivariable Calculus] Flux and Maple Program

    Homework Statement It would help if you guys had access to Maple Anyways here is the problem: http://poibella.org/calc3f11/wp-content/uploads/2011/09/lab_3_vector_calc_F_11.pdf It is on question 12 asking for flux and the questions after that. Homework Equations In the link The...
  10. I

    Flux Integral for a Surface Above a Disc with Downward Orientation

    QUESTION: Compute the flux of the vector field, F , through the surface, S. F = xi+yj+zk S is the part of the surface z = x^2 + y^2 above the disc x^2 + y^2 ≤ 4 , oriented downward. I am just wondering why the integrand is from o to 4 while the radius is only 2.
  11. beyondlight

    Magnetostatics. Calculate the magnetic flux density.

    Problem description: A wery long, than and flat metal plate of width 2a carries the total current I in the z-direction. The current density is uniformely distributed over the metal plate. A point P of particular interest is also shown in the figure, where the point has the position r=ax+ay...
  12. I

    Calculate Field Flux on C: Grad(f)

    Can anyone show me how to do this? http://img853.imageshack.us/img853/739/38647978.jpg http://img21.imageshack.us/img21/3074/62209167.jpg Calculate the flux of the field grad(f) on C.
  13. A

    Find Magnetic Flux: Solve Triangle θ & x0 in xy Plane

    Homework Statement There is a triangle in the upper right hand corner of the xy plane. You are given θ, and x0. Consider an electric field which does not vary with time or the z direction but which varies in the x and y directions according to E=K(x2y, -xy2) throughout the region of interest...
  14. D

    Flux Pinning/Heat Generation in Type II Superconductors

    I don't understand the mechanism by which "flux tubes" create heat, and are pinned by impurities in a type II superconductor. When Bc1<B<Bc2 I understand magnetic flux will penetrate the material in the form of flux tubes. Then the current in the superconductor exerts a force on these tubes...
  15. G

    Induced emf with no change in flux

    If a loop is moved in a uniform magnetic field such that the direction of its motion is perpendicular to the magnetic field, then no change of flux occurs. Then according to faraday, no emf is induced... But I was thinking that can the emf be produced in it due to the deflection force?
  16. S

    Exploring the Effects of Self-Inductance and DC Excitation on Coils

    Hi, When coil is excited with ac because of varying nature of current ,flux of varying nature will be developed in coil and because of varying flux emf will induce in coil. what will happen if coil is excited with dc? intially cureent will increase from zero to maximum and is...
  17. jegues

    Magnetostatics - Magnetic Flux + Force

    Homework Statement See figure attached. Homework Equations The Attempt at a Solution I can follow how he applies amperes law to obtain the magnetic field produce by the wire but I'm extremely confused how he writes the expression for the flux flowing through S. What I...
  18. N

    Is the magnetic flux in a neuron star creation constant? Why?

    I did this problem on this British Physics Olympiad paper and it assumed that when a star bigger than the sun collapses under its own gravity to create a neuron star the magnetic flux stays constant. Please explain Thanks
  19. B

    Maximum flux in a single phase transformer

    A single phase transformer has the following rating: 120 kVA, 2000 V/100 V, 60 Hz with 1000 primary turns. Determine: (a) the secondary turns (b) the rated primary and secondary currents (c) the maximum flux (d) given a maximum flux density of 0.25 T, the cross-sectional area of the core...
  20. D

    Calculating Flux Change and Meaning of Rotating Ring Diameter?

    Homework Statement A ring can rotate about a horizontal axis(x), and a diameter placed on the x-axis. A uniform field is perpendicular to the ring -B0*y. The diameter of the ring is D. it spins with constant angular velocity ω around the x-axis. At at time t = 0 the ring is entirely in the xy...
  21. O

    Determine the radial flux density (jr) of chlorine ions

    Homework Statement A cell 20 microns long and 2 microns in diameter enclosed in a membrane 80 nonometers thick with a dielectric constant of 8 (neglet the ends). The cell has a potential difference between outside and inside of -70 millivolts, calculate the extra chlorine ions that must...
  22. T

    At What Wavelength is the Peak of the Planet's Blackbody Intensity Function?

    Homework Statement Imagine you are trying to detect a Jupiter-like planet located 7.5E11 m from a Sun-like star. At what wavelength is the peak of the planet's Planck blackbody intensity function (assume the planet is a perfect blackbody)? Radius of Planet r = 7E7 m Radius of Star R =...
  23. T

    Electric Flux Density for Coaxial Cable

    Homework Statement I am given the following problem: http://forum.allaboutcircuits.com/attachment.php?attachmentid=35938&d=1320027350 Homework Equations The Attempt at a Solution My known equations and attempt to the problem...
  24. A

    Help with linear charge density and flux

    Homework Statement The y-axis carries a uniform linear charge density of -2 nC/m, and there is a 8 nC point charge at the point (3 cm, 0 cm, 0 cm) as well as a -4 nC point charge at the point (-8 cm, 0 cm, 0 cm). What is the electric flux through a closed spherical surface of radius 4 cm...
  25. J

    Magnetic Flux analysis in transformer design.

    Hello everyone, I'm currently at third year of EPE and this software is totally new for me so i would to ask a few questions. I have been asked to use infolytica MagNet using Field Sampler tool to analyse a flux behavior in the air-gaps and in the transformer core for 2 different core...
  26. P

    Help Me Understand: Magnetic Flux Problem Solution

    I'm having problems understanding this solution (attached.) I don't understand how they got 2*magnetic flux out of the change in the magnetic flux in the bottom of the attachment. Can someone explain that to me?
  27. L

    Solving for net flux, given x- and y- components of electric field, E

    Homework Statement A Gaussian surface in the shape of a cube has edge length 1.14 m. What are (a) the net flux through the surface and (b) the net charge (in C) enclosed by the surface if the electric field in the region is in the positive y direction and has a magnitude that is given by...
  28. Z

    Electric flux charge through a cube

    Homework Statement The electric flux through each face of a 4.50m x 4.50m x 4.50m cube is 130Nm^2/C . How much charge is inside the cube? Homework Equations Electric Flux = E*A = Qin/ε The Attempt at a Solution I know electric flux is given, 130Nm^2/C and I'm trying to solve for...
  29. A

    Calculate the flux (J) Between points x and y

    The diffusion of Ni in FCC Fe. There is 0.3 atoms % of Ni in a solid solution in FCC Fe @ point x. Point y is 1 mm away and has 0.2 atoms % of Ni within the solid solution. Temperature = 1000° C, D = 2ε-16M2/s Calculate the flux (J) between points x & y. Radius of Fe atom = 0.13 nm @...
  30. V

    Calculating Electric Flux Through a Rectangle

    Homework Statement Determine the electric flux through a 6m by 4m rectangular area. The area is oriented such that a vector normal to its surface points in the [1;6] direction. The electric field is [7;1] N/C. Homework Equations Φ=E·A=EA*cosθ The Attempt at a Solution...
  31. J

    Finding Electric Flux and Electric Fields

    I have two questions that I cannot seem to figure out. Homework Statement 1)A uniform electric field E=30 N/C exists parallel to the axis of a square pipe of side length l=5 cm as shown in the figure. Calculate the total electric flux for the slanted face of the pipe 2) A very long metal...
  32. K

    Solving for Flux. Basic Calculus question.

    Homework Statement Basic Question. My book describes the rate of heat transfer per unit of system area as \dot{Q}=\int\dot{q}dA. The Attempt at a Solution I'm trying to solve for the flux. I've already discovered that the correct answer question is just the derivative of \dot{Q} with respect...
  33. T

    Does the converse of Lenz's Law act to compensate for E flux?

    Lenz's Law says that the induced emf from a change in B flux creates a B field that compensates for the flux change. I know that a changing E field induces a magnetic field as well, but does that magnetic field act in a way to compensate for the change in the E field? Or is that not physically...
  34. O

    Calculating Electric Flux through a Cube with Given E-field in Region of Space

    1. The electric field in the region of space shown is given by E=(8i + 2yj) N/C where y is in m. A) What is the magnitude of the electric flux through each face of the cube. (3.0 M sides, 2.0m from yz axis)? B) Is there any charge in the cube? 2. E * da 3. To be honest I have...
  35. Q

    Question regarding the flux of a field.

    I'm currently studying Classical Electrodynamics, and I see everywhere that the flux of a field through a surface is defined as the normal component of the field times the surface area. They interpret this in a physical way as the net charge flowing through the surface in the unit of time. My...
  36. T

    Need Help in Finding Electric Flux through a Hole in Sphere

    Homework Statement An uncharged nonconductive hollow sphere of radius 19.0 cm surrounds a 20.0 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...
  37. A

    Is the Electric Field Normal to the Surface?

    Homework Statement Let's say you have a solid cylinder. It is nonconducting. It is long enough such that the contributions from the ends are negligible. It has a non-uniform volume charge density of Ar^2, where A is some positive constant. Then you are asked to find the electric field at...
  38. K

    Confirming Gauss' Law: Finding Flux

    In general I just wanted to see if I was setting this problem up correctly. We have a cube centered around the origin and a point charge at the origin. The task is to find the flux & confirm Gauss' Law. We are however to complete the integral ourselves. So imagining the top of the cube...
  39. S

    Calculating energy from flux and max wavelength

    hey I am calculating energy of a blackbody emitter, and i have the flux (energy per unit area) and the peak wavelength emitted. how do i calculate total energy?
  40. B

    Net Flux through a cube with a varying electric field only along the Y-axis.

    Homework Statement An E-field is given as \vec{E}y = b\sqrt{y}\hat{j} V/m. Find the net flux through a cube with vertex at (0, a, 0) and side lengths a. (A picture is attached, but it is essentially the cube that would typically be at the origin, shifted along the y-axis by a units) (You can...
  41. Y

    Calculating Electric Flux Leaving a Sphere from Point and Line Charges

    Homework Statement A point charge of 20 nC is located at (4,-1,-3), and a uniform line charge of -25nC/m lies along the intersection of the planes x=-4 and z=6. (a) Calculate D at (3,1,0). (b) How much electric flux leaves the surface of a sphere of radius 5, centered at the origin? (C) Repeat...
  42. DocZaius

    Is Left Side of Gauss' Law equation not the total electric flux?

    Homework Statement The total electric flux from a cubical box 40.0 cm on a side is 4700 Nm^2/C. What charge is enclosed by the box? Homework Equations Gauss Law: surface integral of E-field-vector * dA-vector = Q_enclosed/epsilon naught The Attempt at a Solution The reason I am...
  43. A

    What is the net flux through the box?

    Homework Statement Vector V = <x2yz2, xy3z> 0<=x <=a 0 <= y <= b 0<= z <= c Homework Equations \intV \bullet \hat{n}dS In our case, this amounts \int\intV(either x or y component) dot \hat{i} or \hat{j} dA. The Attempt at a Solution Okay, I have tried to break apart the...
  44. jegues

    Flux out of a Cylindrical Cable

    Homework Statement A coaxial transmission line has an inner conducting cylinder of radius a and an outer conducting cylinder of radius c. Charge ql per unit length is uniformly distributed over the inner conductor and -ql over the outer. If dielectric \epsilon_{1} extends from r=a to r=b and...
  45. L

    Cancel secondary flux (reaction) from transformer

    hi, The drawing show 2 transformers T1 and T2. Each primary of transformer is at fixed voltage (110 volt for example), but one transformer is with 0° phase and other with 180° phase. The secondary of each transformer has the same charge and the same current. The idea is to cancel the flux from...
  46. J

    Electric Fields, Flux, Gauss' Law

    Homework Statement The Electric field E produced by an unknown charge distribution p (rho) is E(r)= (constant)*((exp(-ar))/r^2)*(r_hat). a.) Use Gauss' law in differential for to determine p(rho) b.) Find the total charge q_tot by directly integrating p(rho), and show that it is 0. c.)...
  47. J

    Find the flux through a surface S (Electromagnetic Theory)

    Homework Statement A point charge q1 is located on the y-axis at r1= a (Y_hat) and another q2 located at the mirror point r2= -a (Y_hat). The charges are not necessarily the same sign or magnitude. Now consider the circular surface S of radius a contained in the x-z plane through the origin...
  48. N

    How Do You Calculate Magnetic Flux Through a Cube's Face?

    Homework Statement A cube of edge length 0.05m is positioned as shown in the figure below. A uniform magnetic field given by B = (5 i + 3 j + 2 k) T exists throughout the region. a) Calculate the flux through the shaded face. Homework Equations \phi = B.A cos \theta The Attempt at a...
  49. D

    Electric Flux through Cylindrical Surface

    An infinite line of charge with charge density λ1 = -5 μC/cm is aligned with the y-axis as shown. I am pretty sure you are supposed to use Gauss' Law so I tried just calculating the total enclosed charge and dividing it by epsilon naught, but it's not working. I think maybe I have to use...
  50. T

    Calculating Electric Flux Through a Square Surface

    Homework Statement A square surface, 34 mm each side, is immersed with an electric field of magnitude 1700 N/C. The field lines make a 35 degree angle with the normal line. Find the electric flux through the surface. Homework Equations \ointE\cdotdA The Attempt at a Solution Well, since...
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