What is Magnetic flux: Definition and 366 Discussions

In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted Φ or ΦB. The SI unit of magnetic flux is the weber (Wb; in derived units, volt–seconds), and the CGS unit is the maxwell. Magnetic flux is usually measured with a fluxmeter, which contains measuring coils and electronics, that evaluates the change of voltage in the measuring coils to calculate the measurement of magnetic flux.

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  1. W

    Why Is It Sin Theta Instead of Cos Theta in Magnetic Flux Calculation?

    Homework Statement I had know that for finding magnetic flux is NBA cos theta. The answer is C though, so why is it sin theta instead of cos theta? I wonder Homework Equations BA cos theta NBA cos theta[/B] The Attempt at a Solution
  2. P

    Why Is Magnetic Flux Calculated Using the Solenoid's Area Instead of the Loop's?

    Homework Statement Question asks for the flux through the loop when the loop is both perpendicular and at an angle to the solenoid. solenoid diameter = 2.2 cm loop diameter = 6.8 cm B inside solenoid = 0.22 T Homework Equations ∫B⋅dA = Φ_B The Attempt at a Solution B is constant so can...
  3. T

    Magnetic flux- is this the correct way to solve it?

    Homework Statement As shown below, a rectangular wire loop of height 1.0 m, width 1.5 m, mass 0.10 kg, and resistance 10.0 Ω is pulled into a region of uniform magnetic field with magnitude 1.0 T pointing into the page (perpendicular to the plane of the loop). Determine the force necessary to...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  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. cheapstrike

    Self inductance of a coaxial system of cylinders

    Homework Statement A thin hollow cylinder of radius a is surrounded co-axially by another hollow cylinder of radius b, where b>a. An electric current I flows through them (I is into the plane of paper (x) in outer cylinder and coming out of plane of paper (.) in inner cylinder). Find the: a)...
  12. 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...
  13. 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...
  14. 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...
  15. 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...
  16. 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)...
  17. 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...
  18. 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...
  19. 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...
  20. F

    Exploring the Effects of Lenz' Law and Magnetic Flux: Is Ferromagnetism the Key?

    Why is it that the induced emf opposes the change in magnetic flux? Is it to follow the law of conservation of energy?
  21. H

    Resulting magnetic flux in the core of a transformer

    In a transformer, let's say we have: I1, I2 - currents through the primary and secondary winding V1, V2 - voltages N1, N2 - number of turns F1, F2 - magnetic fluxes through core, produced by the currents I1 and I2 (they are opposing...) R - the reluctance of the core We have V1/V2 = N1/N2...
  22. moenste

    Speed, force, magnetic flux of an ion?

    Homework Statement The diagram shows a mass spectrometer used for measuring the masses of isotopes. It consists of an ion generator and accelerator, a velocity selector and an ion separator, all in a vacuum. In one experiment, tin ions, each of which carries a charge of +1.6 * 10-19 C, are...
  23. moenste

    Calculate the magnetic flux density

    Homework Statement The magnetic flux density in the vicinity of a large air-cored electromagnet is determined by measuring the induced flow of charge in a small coil as the current in the electromagnet is switched on -- see the diagram below. Calculate the magnetic flux density at the...
  24. moenste

    Find direction of current in a magnetic field

    Homework Statement The diagram shows a uniform magnetic flux density B in the plane of the paper. Q and R mark the points where two long, straight and parallel wires carry the same current, I, in the same direction and perpendicular to the paper. The line through QR is at right angles to the...
  25. moenste

    Magnetic flux density between two wires

    Homework Statement Two identical wires R and S lie parallel in a horizontal plane, their axes being 0.10 m apart. A current of 10 A flows in R in the opposite direction to a current of 30 A in S. Neglecting the effect of the Earth's magnetic flux density calculate the magnitude and state the...
  26. W

    Axisymmetric FEA model for magnetic flux distortion

    Why do axisymmetric FEA models of magnets and their fields make the field farther from the axis appear denser than it really is when the flux line mode is enabled? I'm using the F.E.M.M. system at the moment. All integrals and graphs give correct values, but the depicted lines of flux appear...
  27. A

    Position of a coil relative to the magnetic flux

    Does a magnet have to penetrate the plane of a coil in order to generate an emf in the coil? Would an emf be obtained if the coil only passes through the magnetic lines of force, without the magnet crossing the plane of the coil? Thank you.
  28. R

    Magnetic Flux Vectors: How Are Flux Scalar?

    how is flux scalar if the magnetic field and area both are vector quantities?
  29. M

    What does the magnetic flux depend on?

    Homework Statement Does the magnetic flux depend on the shape of the surface or on the enclosed current? Or both or neither? Homework Equations - The Attempt at a Solution I have no clue. I guess a change in the enclosed current is a change in the field and thus a change in the flux, but I...
  30. E

    How Magnetic Flux Causes Load on Generators

    this might have been answer before. Question is, what in physics or chemistry creates a load on a generator when the demand increases. For example, If no lights are turned on connected to a generator, it will spin freely. but the more lights are turned on the harder is to spin the generator...
  31. kamhogo

    Finding the current in a solenoid

    Homework Statement A 40-turn, 4.0-cm-diameter coil with R = 0.40Ω surrounds a 3.0-cm-diameter solenoid. The solenoid is 20 cm long and has 200 turns. The 60 Hz current through the solenoid is I = Io sin (2Πft). What is Io if the maximum current in the coil is 0.20A? Homework Equations Ncoil =...
  32. Drakkith

    Magnetic Flux in a Coaxial Cable

    Let's say we have a coaxial cable with a 2d rectangular surface lying between the inner and outer conductors and running the length of the cable. I'm trying to understand why the magnetic flux through this surface only includes the magnetic field generated by the current flowing through the...
  33. T

    Zero-Divergence of Rate of Change of Magnetic Flux

    Let's introduce a time-varying scalar field ρ(x,y,z,t) [charge density] and vector field J(x,y,z,t) [current density] Assuming the system follows Maxwell's equations, what must both fields satisfy such that ##∇⋅(\frac{∂B}{∂t})=0## ?
  34. gsmtiger18

    Displacement current and magnetic flux through a wire loop

    Homework Statement A long straight wire has a line charge, λ that varies in time according to: λ = λ0e(-βt). A square loop of dimension, a, is adjacent to the wire (at a distance a away from the wire). Calculate expressions for the displacement current at the center of the wire loop and the...
  35. A

    Question about magnetic flux density B

    Magnetic flux density B is a vector quantity and thus represents a force. However most texts state that the magnetic force is perpendicular to the direction of B, which is tangential to the magnetic field line at any give point. I assume that this magnetic force refers to the Lorentz force. So...
  36. TheSodesa

    Mutual inductance of a long wire and a triangular loop?

    I originally posted this to the advanced homework -section, but maybe this isn't advanced enough to warrant being posted there :oops:. If a mod sees this, feel free to delete the original on the other forum. I'd do it myself, but I can't. 1. Homework Statement Calculate the mutual inductance for...
  37. D

    Understanding Magnetic Flux: Integrals vs. Simplified Equations

    Homework Statement So I understand that the magnetic flux is equal to the integral of (B dotted with dA) (new to the site don't know how to use math symbols). My question is, how come in some problems, is it ok to just say the magnetic flux is equal to the magnetic field times the area, while...
  38. S

    Electromagnet magnetic field strength

    Homework Statement Homework Equations ##\oint_{C} Bd\ell = \mu I_{enc}, B_{normal}## continuous across boundary, ##H_{parallel}## continuous across boundary The Attempt at a Solution $$\oint_{C} Bd\ell = \mu I_{enc} \rightarrow B = \frac{\mu NI}{2\pi r}$$ Any help much appreciated. How...
  39. T

    Flux in magnetic core according to special relativity

    Hi, So say you have a magnetic flux in a closed magnetic path circuit (like a TX core). Well I mean we draw arrows and stuff to indicate how the magnetic flux travels, but after watching this: I'm having trouble understanding why there is any flux moving through at all. Can someone please help...
  40. M

    What is the position dependent magnetic field for a Stern-Gerlach experiment?

    Homework Statement For a Stern-Gerlach experiment, there is a apparatus designed to create a magnetic gradient. There is a dipole magnet. The radius of the convex pole is 5 cm, the radius of the concave pole is 10 cm. The convex pole as a 2 T magnetic field along its surface. (The apparatus is...
  41. M

    Find an expression for magnetic flux and calculate

    Homework Statement Loop of wire with the following properties in a magnetic field B. Find an expression for the magnetic flux through the loop and evaluate the magnetic flux at t=25s. The magnetic field is uniform but changes strength at time (t) given by B(t) = B0 exp (kt)Resistance = 20ohms...
  42. S

    Electromagnet which produces varying magnetic flux

    I want to make an electromagnet but it should Produce magnetic flux which changes with time. What material wire would be the best to make make windings?
  43. kostoglotov

    Energy dissipated by a loop of muscle in an MRI machine

    edit: turned out to be a calculator typo...mods feel free to delete this thread if you wish, I won't complain. Homework Statement [/B] Having issues with part a) imgur link: http://i.imgur.com/4hzLyhb.jpg Homework Equations Resistivity of muscle (from table in text): \rho \approx 13...
  44. T

    Calculating Magnetic Flux Needed for Ion Control

    Homework Statement A magnet is used to control negative ions and only allow those with a specific mass to pass through a narrow gap opening . The magnet will bend the ion beam in a quarter circle of radius 50 cm . In an experiment, a negative ion accelerated by a voltage of 3.0 kV. Which...
  45. pecchiaw12

    Trouble understanding - to + vs + to - current flow

    Homework Statement When reading about directions of magnetic flux in relation to current flow on pages 6 to 8 of http://www.free-energy-info.tuks.nl/Non-Ferrous-Magnet.pdf , I found that in figure 11 the current is traveling from + to - terminals, while in figure 12, the current flows from - to...
  46. I

    Magnetic Flux Linkage: Rate of Change & Cutting

    Hi, this may be really easy but.. I understand that to have an induced e.m.f , we can either have a rate of change of magnetic flux linkage ( ac source ) or cutting of flux ( like a plate oscillating and cutting through a magnetic field produced by a solenoid ). However does cutting of flux...
  47. G

    Electromagnetism help: Find magnetic flux through a loop

    Homework Statement Very large conductor with DC current is in vacuum. Find magnetic flux through a loop. Given parameters: I,a,\alpha Homework Equations \Phi=\int_S B\mathrm dS - basic equation for magnetic flux B=\frac{\mu_0I}{2\pi x} - electromagnetic induction created by very long...
  48. D

    Magnetic Flux Density Direction

    Would the direction of the Magnetic Flux Density vector B at the south side be towards the south pole like this? and is the direction for B correct for the other side? One more thing, how can magnetic flux density be a vector and have a direction when its sort of a density, I mean its over an...
  49. D

    Magnetic Flux in a Solenoid

    Homework Statement A single-turn square loop of side L is centered on the axis of a long solenoid. In addition, the plane of the square loop is perpendicular to the axis of the solenoid. The solenoid has 1280 turns per meter and a diameter of 5.85 cm , and carries a current of 2.15 A . Find...
  50. Salvador

    Exploring Magnetic Flux Path in Coil Wound on a Solenoid

    Hi, I was wondering about a simple example.take a coil wound on a solenoid, one side of the solenoid core is permanently attached to a permanent magnet S pole, the other end of the solenoid core is not attached to any magnet. Now I take another magnet turn it with the N pole facing the solenoid...
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