# What is Magnetic flux density: Definition and 52 Discussions

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the magnetic field. A permanent magnet's magnetic field pulls on ferromagnetic materials such as iron, and attracts or repels other magnets. In addition, a magnetic field that varies with location will exert a force on a range of non-magnetic materials by affecting the motion of their outer atomic electrons. Magnetic fields surround magnetized materials, and are created by electric currents such as those used in electromagnets, and by electric fields varying in time. Since both strength and direction of a magnetic field may vary with location, they are described as a map assigning a vector to each point of space or, more precisely—because of the way the magnetic field transforms under mirror reflection—as a field of pseudovectors.
In electromagnetics, the term "magnetic field" is used for two distinct but closely related vector fields denoted by the symbols B and H. In the International System of Units, H, magnetic field strength, is measured in the SI base units of ampere per meter (A/m). B, magnetic flux density, is measured in tesla (in SI base units: kilogram per second2 per ampere), which is equivalent to newton per meter per ampere. H and B differ in how they account for magnetization. In a vacuum, the two fields are related through the vacuum permeability,

B

/

μ

0

=

H

{\displaystyle \mathbf {B} /\mu _{0}=\mathbf {H} }
; but in a magnetized material, the terms differ by the material's magnetization at each point.
Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature.
Magnetic fields are used throughout modern technology, particularly in electrical engineering and electromechanics. Rotating magnetic fields are used in both electric motors and generators. The interaction of magnetic fields in electric devices such as transformers is conceptualized and investigated as magnetic circuits. Magnetic forces give information about the charge carriers in a material through the Hall effect. The Earth produces its own magnetic field, which shields the Earth's ozone layer from the solar wind and is important in navigation using a compass.

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1. ### On the magnetic dipole radiation in Griffith's book

In 11.1.3 of Griffith's "Introduction to Electrodynamics 4Ed" appears magnetic dipole radiation, which results in the equation above. According to the resultant equation, there is no magnetic field in the axis of the wire loop because theta=0. However, I think the magnetic flux density is at...
2. ### I Magnetic Flux - Misleading Definition or what?

Magnetic flux density(B) is defined as, magnetic force per unit pole strength and flux is defined as magnetic field passing normally through given surface. I think, I am clear about these definitions, and quantitative meaning they carry. I usually find, in some texts, the definitions as in image...
3. ### Relationship between magnetic field lines and magnetic field

As stated in the problem, I want to demonstrate mathematically that field line density is directly related to the magnitude of B. How would I be able to do this, other than simply using the flux equation and showing that for a higher flux in the same area, the magnetic field must be rise...
4. ### Is the magnetic flux density B constant?

Summary:: Is the magnetic flux density B constant? Is the magnetic flux constant? I am working on a project design for Uni and I am stuck. In a magnetic circuit is either the magnetic flux or the magnetic flux density B constant? This magnetic circuit has all different cross section areas and...
5. ### Magnetic field lines and magnetic flux density

I'm trying to understand the relationship between the "number" of field lines passing through a region and the magnetic force in this region.I understand that the drawings are of course conceptual: we cannot draw "all" the field lines (although can be visualized with iron fillings).Also the...
6. ### Magnetic flux density of a relativistic electron

q = 1.602e-19C mass_electron = 1.098e27 c = 3e8 Omega(Mag_flux_den) = 5GHz Lorentz factor = 100 synchrotron radiation at frequency v = 5GHz Mag_flux_den = (Omega(Mag_flux_den) * c * Mass_electron * Lorentz factor) / mass_electron Mag_flux_den = (5000 x 3e8 x 1.098e27 x 100 ) / 1.602e-19 =...
7. ### Engineering How can I find this formula for the magnetic flux density? (EMagn)

I drew an illustration to make this easier: Point P is where I wish to find the magnetic flux density H. Given the Biot-Savart formula: $$d\textbf{H} = \frac{I}{4\pi}\frac{d\textbf{l}\times\textbf{R}}{R^2}$$ I can let $$d\textbf{l} = \hat{z}dz$$ and \hat{z}dz\times\textbf{R} =...
8. ### Why am I getting Maxwell's second equation wrong?

While going through an article titled "Reflections in Maxwell's treatise" a misunderstanding popped out at page 227 and 228. Consider the following equations ##(23\ a)## and ##(23\ c)## in the article (avoiding the surface integral): ##\displaystyle \psi_m (\mathbf{r})=-\dfrac{1}{4 \pi} \int_V...
9. ### I Showing that B has no discontinuities at the surface

Consider a magnetic dipole distribution in space having magnetization ##\mathbf{M}##. The potential at any point is given by: ##\displaystyle\psi=\dfrac{\mu_0}{4 \pi} \int_{V'} \dfrac{ \rho}{|\mathbf{r}-\mathbf{r'}|} dV' + \dfrac{\mu_0}{4 \pi} \oint_{S'}...
10. ### Ratio of the Electric field to the Magnetic field

Dear all. I would like to know the general expression of the ratio of the electric field strength E to the magnetic flux density B. I know E/B = c, where c is the speed of light, for a vacuum, but I want to know if this is stil valid for any material where the electric and magnetic fields are...
11. ### The magnetic flux density at point P between parallel wires

Homework Statement In the picture at points A and B are two thin parallel wires, where traveling currents are 15 A and 32 A to opposite directions. The distance between wires is 5.3 cm. Point's P distances from A and B are the same. Calculate the magnetic flux density at point P. Homework...
12. T

### Temperature and magnetic flux density

Hello all; I am new in this forum, currently in High School. For some time now, I have been looking online for a relationship between temperature and magnetic flux density of a ferromagnet; below the Curie point. However, I can't seem to find any relationship or formula. Do any of you know...
13. ### Magnetic Dipole Field from a Loop of Wire

I am trying to understand the magnetic dipole field via loop of wire. The above pictures show how this problem is typically setup and how the field lines are typically shown. The math is messy but every textbook yields the following: β = ∇xA = (m / (4⋅π⋅R3)) ⋅ (2⋅cos(θ) r + sin(θ) θ) The...
14. ### 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...
15. ### 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...
16. ### 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...
17. ### 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...
18. ### 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...
19. ### The Magnetic Force on an Iron Ring

I decided to simulate this scene in Lord of the Rings for a project in school with the purpose of calculating the "real" mass of the One Ring. I've done the experiments according to this principle sketch but I have some troubles with calculating the magnetic force that the copper coil is...
20. ### I need to create a .7+ Tesla electromagnetic solenoid

I am trying to create a solenoid with a high flux density, but I need the specifications (wire gauge, current applied, etc). The diameter of the core would be preferable around 15mm. The length can be pretty much anything reasonable. I need this for a project that requires a strong repulsive...
21. ### 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...
22. ### 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?
23. ### 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...
24. ### 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...
25. ### 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 =...
26. ### Magnetic flux density calculation for high permeability material

Hi to all of you, As the Biot-Savart-Law is based on experimentations in air, i like to know how to calculate the magnetic flux density in material with much greater permeability, where the circular like shape of the field distribution troughout the vicinity does not apply. Does anyone has a...
27. ### Connection between coloumbs , ohms and magnetic flux density

what is the connection between coloumbs , ohms and flux !
28. ### Magnetic Flux Density vs Magnet Geometry

Gentlemen, the the image shows 2 N48 neodymium magnets of the same volume 54 in2. On several website I can use magnetic flux density calculators to get the Br of the rectangular magnetic but haven't found one that calculates the value of the arc magnet. The Br value of the rectangular magnet is...
29. ### 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...
30. ### Trying to increase the magnetic flux density

Hello all, long time follower, first time poster. (Also feel free to move this if it's not in the right section.) Basically I have this mechanism pictured here: You can imagine that the drawing is of a top view of a section cut of the total mechanism. This is the radius view, the full diameter...
31. ### What is magnetic flux and magnetic flux density? Please keep it simple.

Im revising for my A levels and I could really do with a simple, straight forward definition for magnetic flux and magnetic flux density. Can anyone please help? I'd be very grateful. F=BIl ∅=BA
32. ### 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...
33. ### Calculate the value of magnetic flux density in air

Homework Statement Calculate the value of magnetic flux density in air in the middle of two straight parallel wires carrying currents of 10A and 20A in the opposite directions. The distance between wires is 10cm. The Attempt at a Solution \oint \vec{B}\cdot d\vec{A} = \Phi \oint \frac{\mu_0...
34. ### Magnetic flux density in the centre of a current carrying loop

Homework Statement A current carrying loop of wire is being monitored using a Hall-effect magnetic field probe placed at its centre. The loop is in air and has a radius of 0.5 m. It is required to monitor the magnetic flux in order to trip the circuit breaker if the current exceeds 100 A...
35. ### Vector potential and constant magnetic flux density

Hi, I would like to verify analytically that a vector potential of the form A=1/2(-yB0,xB0,0) produces a constant magnetic flux density of magnitude B0 in the z direction. (I guess I'd have to use the relation B=\forall\wedgeA...)
36. ### Measuring Magnetic Field Intensity (H) and Magnetic Flux Density (B).

Now here is a real world practical application. Australia Post has a warning for shipping magnetic material in the post. Section D2.9.2 states... Any material that, when packed, has a magnetic flux density of 0.159 A/m or more at a distance of 2.1 meters from any point on the surface on the...
37. ### Calculating Magnetic Flux Density in a Solenoid

The magnetic flux density B( in tesla ) inside the solenoid and parallel to its axis is given by the expression B= permeability of free space x n x I, where n is the number of turns per metre length of the solenoid my question is so for example, if n = 100turns in 1m and I = 2Ampere...
38. ### Magnetic fieldstrength, magnetic flux, magnetic flux density

I have a problem understanding magnetic fieldstrength, magnetic flux, magnetic flux density. Some questions that answered may ease my understanding: Is it true that the magnetic field strength B in the core caused by a current in a wire wound on a the same torodial magnetic core is...
39. ### Normal/Tangential magnetic flux density problem

[PLAIN]http://img232.imageshack.us/img232/7172/60746674.png Homework Statement The picture attached to this question shows a magnetic slab with μr = 50. A thin conducting film (with μr = 1) lies on top of the slab and carries a surface current of 1.0[A/mm] directed out of the page. If...
40. ### Calculating Magnetic Flux Density in a Hollow Cylindrical Conductor

π²³ ∞ ° → ~ µ ρ σ τ ω ∑ … √ ∫ ≤ ≥ ± ∃ · θ φ ψ Ω α β γ δ ∂ ∆ ∇ ε λ Λ Γ ô Homework Statement An arbitrarily long hallow cylindrical electric conductor shown carries a static electric current density J=\hat{z}J0. Determine the magnetic flux density B in the hallow region of radius a. Your result...
41. ### How Does Copper Wire Shape Affect Magnetic Flux Density?

A 1mm-diameter copper wire is shaped into a square loop of side = 4cm. It is placed in a plane normal to a magnetic field increasing with time as \vec{B}=1t\hat{z}Wb/m2. Calculate the magnetic flux density at the center of the loop. I found that the magnitude of the induced current is...
42. ### Magnetic flux density vs magnetic flux

i'm having trouble distinguishing between magnetic flux and magnetic flux density...can someone please explain to me? also why is it sometimes used interchangeably?
43. ### Magnetic Flux Density in a Circular Loop

Homework Statement A current flows in a circular loop consisting of a single turn.If the same wire is bent into a circular loop of 2 turns and the same current is passed through the loop,the magnetic flux density at the centre will change by a factor of ...? (ans: 4 ) Relevant equations B...
44. ### No Such Thing As Magnetic Flux Density

I would like to put this out for argument that there is no such thing as magnetic flux density. Since magnetism is a wave like on water's surface, it is continuous. Is there a 'water wave density?" I think not. Unless you mean the distance between wave peaks. But flux lines are only arbitrary...
45. ### Magnetic Flux Density at different points about a solenoid

Homework Statement For my physics investigation I am required to first find the theoretical magnetic flux denisty at different points about a solenoid. The points are outside the solenoid: along the axis but past the ends and; perpendicular to the centre of the solenoid but outside. So far...
46. ### Divergence of magnetic flux density

Homework Statement This is from my textbook Engineering Electromagnetics by John Buck and William Hayt 7th Edn, pg 238 in the chapter titled "The Steady Magnetic Field": Homework Equations Divergence theorem: \oint_S \textbf{B} \cdot d\textbf{S} = \int_{\mbox{vol}} \nabla \cdot...
47. ### Magnetic Flux Density: B, \phi, H - True or False?

magnetic flux density is denoted by the B symbol magnetic flux is denoted by the \phi symbol so why do people use B as if they were referencing to magnetic flux? "magnetic flux density is a measurable quantity indicating the strength of a field" ...this was stated by a teacher of...
48. ### How Do You Calculate Magnetic Flux Density on a Solenoid's Axis?

Homework Statement Determine the magnetic flux density at a point on the axis of a solenoid with radius b and length L, and with a current I in its N turns of closely wound coil. Homework Equations Biot-Savart law: myI/(4pi)integral(dlcross er/R^2) there er is the unit vector in...
49. ### Component of magnetic flux density - huh?

hiya If 'b' is the length of a wire, and 'I' current running trough it, then if put a wire inside magnetic field ( not perpendicullary and also not parallel to magnetic field lines, but some angle in between the two ), then magnetic force on a wire will be: F = I * b * B * sin[angle] where...
50. ### Infinitisemal magnetic flux density

These Q's are probably simple for those of you who have/completed a course in Vector Calculus. But I'm only a higschool/secondaryschool student, so I haven't. 1. I'm not sure how the infinitisemal magnetic flux density d\textbf{B} from a wire element d\textbf{l} with a current I, which is...