What is Magnetic field lines: Definition and 53 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,







{\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.

View More On Wikipedia.org
  1. A

    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...
  2. I

    Directing magnetic field lines by using diamagnetic material

    I want to improve the magnetic field strength at the surface of a magnet configuration by utilizing diamagnetic materials to guide the magnetic field lines. I have not the proper equipment to measure the effect myself but would this work? This is the initial configuration with four magnets side...
  3. SamRoss

    Magnetic field lines around electron and wire seem to contradict

    In the picture below, the direction of the magnetic field lines can be determined by using the right-hand rule with the thumb pointing in the direction of the current. If we use the right hand rule in the picture below, thinking of the yellow arrow as the current, we would not get the correct...
  4. Luke2642

    Force & energy in cutting and stretching magnetic field lines?

    I have an ordinary switchable magnet for holding tools to a lathe. It's like a magnetic force gearbox, but I can't quite understand the force multiplication. When placed on a steel surface the switch force is approximately ~5N on both finger and thumb at 1.5cm radius acting over a 3cm arc...
  5. A

    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. M

    Magnetic field "lines" confused with magnetic field "vectors"

    I might be a slow learner, but am still trying to understand the difference between field lines and vectors. I've got that magnetic field lines are symbolic and that the directional arrows applied (from north to south) are a convention. But see the attached image. The field lines form a closed...
  7. Ibix

    Are Magnetic Field Lines Real? - Comments

    Greg Bernhardt submitted a new blog post Are Magnetic Field Lines Real? Continue reading the Original Blog Post.
  8. F

    Evidence for global magnetic grid or pseudo science?

    In conducting research into historical accounts of Earths magnetic field, I consistently come across proposals of stable planetary magnetic grid systems; many of these theories which have apparently been developed through much time and effort. While I am unaware of any theory that cannot be...
  9. A

    Understanding the Relationship Between Magnetic Field Lines and Force

    Hello, I am unable to understand a certain (important) concept. We all know what the field lines of a permanent magnet look like. They go from north to south, and curve around the magnet. This direction (direction of the magnetic field) does NOT describe the direction of a force. And that's...
  10. C

    Magnetic field lines directed?

    Is it possible to direct or confine field lines to be shaped like a laser? I know there are magnets such as neodymium cones that direct field lines through the tip but they don't seem to have the amount of pull as I'm looking for. If there isn't, is there anyway to amplify the power? Maybe align...
  11. T

    Why does the solar wind follow magnetic field lines?

    My physics teacher said that the northern lights are the product of charged particles coming from the sun and interactign with our atmosphere. I believe he said that these are deflected by Earth's magnetic field and directed towards the North and South poles. When I look at pictures on this...
  12. G

    Are particles accelerated along magnetic field lines?

    I have a question which puzzled me when I was reading up about auroras. When talking about the interaction of the solar wind and the Earth's magnetic field, the book said that "particles are accelerated along magnetic field lines towards the earth" That didn’t sound quite right, as I was taught...
  13. P

    Em waves and magnetic field lines

    So i know that magnetic field lines are closed, in an electromagnetc wave how can be these lines closed? i cannot picture this in my head
  14. M

    Plotting magnetic field lines between two adjacent NS poles

    This question is regarding the magnetic field lines around two abutting alternating poles. Take two axially magnetised disc magnets and place them next to each other (like tangent circles), so on each side the adjacent or neighboring magnet is of the opposite pole. By sprinkling iron filings...
  15. Tom-Physics

    Magnetic field lines and the Sun

    Homework Statement Hey! I have trouble with an exercise that I need help with. Here it is: The magnetic field lines for the average interplanetary magnetic field (IMF) follow Archimedean spirals. i) Find the heliocentric distance r in Astronomical Units (AU), where a field line has wrapped...
  16. A

    Magnetic field lines form loops?

    Apart from the orientation of a compass needle and the pattern formed by iron filings, what other proof do we have of magnetic field lines forming loops?
  17. K

    Electric and Magnetic Field lines

    Homework Statement The figure shows crossed uniform electric and magnetic fields and, at a certain instant, the velocity vectors of the 10 charged particles listed in the table. (The vectors are not drawn to scale.) The speeds given in the table are either less than or greater than E/B (see...
  18. M

    Help illustrating magnetic field line vectors and gradients

    Magnetic field lines around multipolar magnets get quite complex. There are local field vectors and field gradients in the x, y, & z plane. In the following diagrams I have tried to illustrate field lines around a centrally (half and half) charged disc magnet. The top diagram represents the...
  19. O

    Potential magnetic field lines and Stokes theorem....

    Hi, A potential magnetic field has no curl. According to the "curl theorem" or stokes theorem, a vector field with no curl does not close. Yet, Maxwell's equation tell us we shall not have magnetic monopoles, so the loops have to close... ? What am I missing to remove this apparent paradox of a...
  20. ATY

    Coronal hole and magnetic field

    Hey guys, I have a question. I am doing some homework for university and got super confused (probably just messing up things). So in school you learn that magnetic monopols do not exist. But my question is now: On the sun there are coronal holes, region where the magnetic field is not able to...
  21. rumborak

    "Reconnection" of magnetic field lines

    This is a bit vague, but I remember reading that during stuff like coronal ejections, magnetic field lines "reconnect". Now, does that not suppose "loose" magnet lines in the process? Which to my understanding do not exist?
  22. L

    Pictures of Magnetic Field Lines

    I have looked in vain on the web for pictures of magnetic field lines for multiple linked current loops. I would be happy just to see a picture of the field lines for a simple Hopf link but somewhere there must be pictures for the Borromean rings and other more complex links - and also braids...
  23. H

    Understanding Magnetic Field Lines: Fact or Fiction?

    Are magnetic field lines actually lines? To me, they are just a way to pictorially represent the magnetic field, and there are no lines. BUT, whenever you do the experiment with magnetic filings on a piece of paper, they align in actual lines. HELP!
  24. H

    Magnetic field lines in a ring magnet

    Say if I magnetize a hollow cylindrical ring magnet by placing a staight current carrying wire along its axis. It will be magnetized with magnetic field lines running inside the cylinder clockwise or anticlockwise! So there will be no magnetic field lines outside the iron body? If I have a...
  25. J

    Magnetic Field Lines around a Magnet

    Hi, please could someone explain why the magnetic field is stronger at the poles of a magnet. I know that the field line density is strongest at the poles and more spaced out in the middle. I get that. I just wanted to know why the magnetic field is stronger at the poles than the middle of a...
  26. C

    Magnetic field lines of earth

    I need help understanding a certain problem. It basically stated: an airplane accumulated a positive charge, heading westward above the equator. Find the direction of the force (using the lame right hand rule thing). The problem I had was figuring out was whether the magnetic field would hit...
  27. M

    What's wrong with this diagram of magnetic field lines?

    I was looking through a book on magnetism and it had the attached diagrams of field lines and stated that the classical diagram of field lines exiting the N pole and entering the S pole is incorrect. They claim their diagram is the correct representation of the magnetic field lines. Their...
  28. A

    Magnetic Field Lines: What Causes Gaps?

    Hello All, I was just checking magnetic field lines as in attached figure. I am curious to see some gaps between adjecent field lines in the figure. Why it is not like a sheath( for example in lighting field) but as lines? Thanx in advance Abraham
  29. Entanglement

    Wire cutting magnetic field lines

    I have read in my schoolbook that when a wire of length l moves at velocity v in a magnetic field cutting the flux lines an emf is induced which it is calculated from emf = blv, I understand that emf is induced at time variation of magnetic flux across the wire, but I Can't see any change in the...
  30. T

    Calculating Magnetic Field Lines

    I guess this is maybe more of a vector calculus question, but here it goes. Say I have an arbitrary current distribution \vec{J} with the corresponding magnetic field given by \vec{\nabla}\times\vec{H} = \vec{J} \vec{\nabla}\cdot\vec{H} = 0 What is the best way to calculate the field/flow...
  31. R

    Magnetic field lines through copper

    Hello. Assume an electron gun, as in CRT, made of plumbing copper instead of glass. Using magnetic scanning coils to move electron beam. Will the displacements of this beam be linear as if tube material was made of glass ? PS : this is not an exercise by though but a real problem I encounter in...
  32. mesa

    Quetion about direction of magnetic field lines

    I see textbooks assign directions to magnetic field lines, for example north poles extending outward and south flowing inward. Are these directions correct or just a way to help tie the concept together and have just been arbitrarily picked much in the same way as conventional current?
  33. S

    Magnetic field lines of current carrying conductor follow property ?

    The lines of flux of the magnet possesses the following properties: 1)Forms closed loop 2)Starts from N-pole and closes at S-pole 3)Do not intersect each other 4)Parallel line and same direction repels each other 5)Parallel line and opposite direction attract each other So...
  34. K

    A Plot of Magnetic Field Lines

    Hi, I was wondering - In the plots that we see of magnetic lines of force (like this one) what exactly are they plotting against what? Meaning is it Bx vs x vs y, or is it Bx vs By vs Bz?
  35. S

    How Do Magnetic Field Lines Break?

    When people talk about sunspots and the solar cycle and stuff like that, they often mention magnetic field lines poking through the surface of the sun. I'm pretty sure I get why the magnetic field lines would be twisted up by the non-uniform rotation of the sun, and why they would poke out of...
  36. A

    Magnetic field lines direction.

    It might seem trivial for most of you but i am confused by the definition of direction of magnetic lines. It's well known the magnetic field is directed from S to N but if one looks from outside and follows the magnetic line then one come from N to S. I am aware of that magnetic lines are closed...
  37. 5

    Magnetic field lines in a current carrying circular loop

    I wanted to ask that do each point of the current-carrying circular loop would create a magnetic field and hence the magnetic field lines? And if yes wouldn't the field lines produced by each point of the loop would intersect each other? I read somewhere that magnetic field lines never...
  38. F

    Magnetic Field Lines Formula (3D)

    Curious as to whether there's a formula for calculating the shape of the magnetic field lines, including electro magnets (solenoids). I want to create a 3D graphical display for the magnetic field lines of magnets.
  39. M

    Magnetic field lines What do they exactly mean?

    Now this might seem like a really stupid question but I'm just a high school student so please bear with me. I've been studying about magnetic fields and my teacher says (everyone does in fact) that in a magnetic field, the magnetic field lines start from the north pole and end in the south...
  40. J

    Magnetic Field Lines: Proving c(T)=c(0) with T≠0

    Suppose that a function B:\mathbb{R}^n\to\mathbb{R}^n and c:\mathbb{R}\to\mathbb{R}^n are defined such that c is differentiable, and \dot{c}(t) = B(c(t)) for all t. The question is that what must be assumed of B, so that it would become possible to prove that c(T)=c(0) with some T\neq 0?
  41. Q

    Magnetic Field: Are Lines an Illusion?

    I have seen people write that there are no such things as "field lines", but that the magnetic field is a continuum. But iron filings on a paper over a magnet will arrange on lines of the magnet's field...Is this an illusion, or are there "lines" that make up the field?...thank you
  42. M

    What's the causal model for direction of curl of magnetic field lines?

    untruncated version of question: As electrons move through a wire, is the direction of the curl of the magnetic field lines observed derivable from an underlying property? =========================== more detail (only to further clarify my question as useful): > looking for a mechanistic...
  43. Q

    6) How does computer software plot magnetic field lines?

    How does computer software plot magnetic field lines where the density of lines represent flux density? How does the software know which points to start plotting from in order to come out with a true representation?
  44. D

    How can magnetic field lines snap ?

    How can magnetic field lines "snap"? In astronomy, magnetic field lines around stars or planets are sometimes said to "snap" and release their stored energy. e.g. the aurora borealis is created that way http://www.atoptics.co.uk/highsky/auror2.htm Also gamma ray bursts of neutron stars...
  45. Q

    Magnetic field lines of a moving electron

    A moving electron's magnetic field lines. How do the magnetic field lines of a moving electron in a straight line look? What about the magnetic field lines of a rotating hydrogen electron? I mean the magnetic field produced due to the electron's intrinsic spin and due to its movement in a line...
  46. B

    Magnetic Field Lines: Explaining Iron Filings Behaviour

    The magnetic field surrounding a bar-magnet (for example) is continuous. The lines that are drawn to depict the strength and direction of the field don't actually exist. They are akin to drawing contours on an OS map, are they not? What therefore explains the behaviour of iron filings when...
  47. I

    Finding the force of magnetic field lines

    Homework Statement A wire carrying 15 A of current has a length of 17 cm in a magnetic field of 0.80 T. The force on a current-carrying wire in a uniform magnetic field can be found using the equation F = BIL sin θ. Find the force on the wire for each of the following angles between the wire...
  48. L

    High & Low Resistivity Effects on Magnetic Field Lines

    Homework Statement Two of the MHD equations can be formulated as \vec{E} + \vec{v} \times \vec{B} = \eta \vec{J} \nabla \times \vec{B} = \mu_0 \vec{J} where [itex]\eta[/tex] is the resistivity of the plasma. a.) Derive an equation for the magnetic field at very high resistivity and...
  49. P

    Understanding the Direction of Magnetic Field Lines to Coil Diagrams

    Magnetic Field Lines Question http://img101.imageshack.us/img101/9819/coil2sm.jpg Could someone tell me which is the direction of these magnetic field lines and why?