What is Magnetic fields: Definition and 673 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.

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  1. G

    I When to properly use "voltage"

    Hi. I'm confused about the usage of "voltage". Some scripts I read introduce it in electrostatic as potential difference (where there's only the scalar potential), but continue using it when changing magnetic fields are present ("induced voltage"). Others make a clear distinction and introduce...
  2. M

    What happened to "the Ballad of Maxwell's equations" sung to the tune of A-Ha, "take on me"?

    Hi folks, I know that this exists. I used to be able to find it. But not anymore. It goes something like "Gauss and Faraday, had a lot of thing to say about magnetic fields" and on and on. I hope that it still exists but I have not been able to find it anywhere. Thanks Tom
  3. Shreya

    Does a linearly time varying B create changing E?

    As accelerated charges produces time varying electric field which produces time varying magnetic fields and so on. I know there is something wrong with my argument, I can't point it out. Please be kind to help.
  4. cutielollipop

    Electromagnetism question -- Forces between two current carrying wires

    Here is the question. I just wanted to confirm and see if I'm understanding the question clearly. For 3a) I said the first wire would have the magnetic field going in a counter clock wise direction and the second wire would have a magnetic field going in a clockwise direction using the right...
  5. M

    Faraday's law and Magnetic Fields

    I am not really sure which direction i am moving in with this solution
  6. S

    Exploring Propulsion with Light & Magnetic Fields

    while browsing for new propulsion methods I found the following interesting: https://en.wikipedia.org/wiki/Radiation_pressure "Radiation pressure (also known as light pressure) is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the...
  7. milkism

    Electric and magnetic fields of a moving charge

    Part a) My solution: Big R basically becomes r, and the electric and magnetic field lines are doubled because of superposition principle. Am I right?
  8. S

    I Behaviour of Magnetic Fields Underwater

    I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean. There is an awful lot of conflicting information online. Ultimately, I'd like...
  9. Drakkith

    Resources on Simulating Charges in Magnetic Fields

    Hey all. I started messing around with making a simulation involving charged particles moving in magnetic and electric fields and I was wondering if anyone had any good resources on the subject. I should be fine on equations, as I already have a book that should have everything I need about the...
  10. PlanTer254

    B Magnetic fields attracting two disc-shaped magnets

    I had 2 small magnets in my mouth for distraction while working on something else,and I had this wierd question.the two magnets were not that strong,so just a force was easy to separate them with my teeth.then they would attract to be attached to each other and then the question hit me,the 2...
  11. Lotto

    B What magnetic fields can this hollow rod shield?

    I suppose it can shield only the external magnetic field, not the field of the magnet itself. But I am not completely sure.
  12. M

    I Fundamental - Magnetic fields generated by moving electrons

    Trying to understand something fundamental about how magnetic fields are generated by moving electrons in a conductor. I have read many forums, studied Emag and am left with more questions. Looking for some practical insight not Bio-Savart derivations, etc. These still do not explain why the...
  13. S

    B Lorentz Transformation of Electric & Magnetic Fields Visualized

    I made a tool for calculating and visualizing how the electric and magnetic fields transform under a Lorentz boost. Thought I'd share it here, in case anyone finds it interesting. https://em-transforms.vercel.app/
  14. warrenchu000

    Why is magnetic field B along a straight wire circular not radial?

    Statement: The magnetic field around a straight wire carrying a current can be explained Relativistically by changing the inertial frame of reference to the frame of the moving electrons - i.e., a Lorentz contraction of the positive charges in the wire will give a denser concentration of the...
  15. P

    I Defining the Forces from Magnetic Fields and Electric Fields

    We define Electric Field Intensity vector at a point as the force experienced by a unit positive charge kept at a point. Is it correct to define B vector similarly that is, is B vector the magnetic force acting on an unit magnetic north pole and is it correct to call B vector Magnetic Field...
  16. V

    I Induced electric fields and induced magnetic fields confusion

    So changing magnetic fields induce electric fields (Faraday's law when the magnetic field is changed by either moving the source or by changing the current in the source that's causing the magnetic field, ie. we're not moving the conductor where an emf is induced so there's no f=qvXB). Also...
  17. bbbl67

    B Are magnetic fields generated through radio frequencies?

    I seem to hear about huge astronomical events that generate radio waves seem to come from objects with huge magnetic fields, such as neutron stars and black holes. Does that mean magnetic fields only come from the radio end of the spectrum, and not higher frequencies, like IR, UV, X-rays, etc?
  18. A

    I Does electron beam in empty space generate magnetic fields?

    Does electron beam in empty space generate magnetic fields around them just as with current in conductor. If yes, then is it experimentally proven that two parallel electron beam would attract each other.
  19. S

    I Magnetic fields are exceptions to the second law of thermodynamics?

    Einstein famously said “{Thermodynamics} is the only physical theory of universal content, which I am convinced, that within the framework of applicability of its basic concepts will never be overthrown.” I don't think any of us want to argue with Einstein, but it's worth noting the "within the...
  20. Mr_Allod

    Edge States in Integer Quantum Hall Effect (IQHE)

    Hello there, I am having trouble understanding what parts b-d of the question are asking. By solving the Schrodinger equation I got the following for the Landau Level energies: $$E_{n,k} = \hbar \omega_H(n+\frac 12)+\frac {\hbar^2k^2}{2m}\frac{\omega^2}{\omega_H^2}$$ Where ##\omega_H =...
  21. R

    I Relation between electric & magnetic fields in terms of field strength

    Hi. A electromagnetic wave consists of an electric and a magnetic component. I believe that the electric field strength is measured in volts per meter. The magnetic field I think is measured in Tesla. Let's imagine that I measure the electic field strength of two different radio stations and...
  22. B

    I Induced Electric and Magnetic Fields Creating Each Other

    Hi, We know that a varying magnetic field creates and induced electric field, and a varying electric field creates an induced magnetic field. If there is a varying electric field (let's say sinusoidal), then this electric field creates an induced magnetic field. And if this produced magnetic...
  23. G

    B Magnetic Fields and Particle Movement: How Do Magnets Affect Electrons?

    I was wondering -- does a magnetic field repel or attract electrons ? Also when you place two magnets together with the same polarity and you feel that pressure - what is this called and can protons or electrons pass through this field -- thanks for the help
  24. F

    How can I detect magnetic fields which are weaker than the Earth's?

    I don't have access to high power systems, or ultra precise detectors.(around 10V/ 1A) Can I detect small variations (frequencies ?) of magnetic field, while ignoring the noise caused by the Earth's magnetic field ? My goal is to measure the magnetic field through a line in order to trace it...
  25. R

    B Coupling Magnetic Fields: Does Orientation Change Strength?

    Magnetic fields coupling question. I had to make a small tool holder for my drill press, it hangs on side of press using N52 cylinder magnets. The holder is 4" long x 3/4 x 3/4" AL bar. With a spacing of 3", two 1/2" holes are bored to accept the 1/2 x 1/2 N52's, which will be epoxied in. I...
  26. elcaro

    I Can magnetic fields explain anomalous galaxy rotation curves?

    Magnetic fields as an alternative explanation for the rotation curves of spiral galaxies ABSTRACT THE flat rotation curves of spiral galaxies are usually regarded as the most convincing evidence for dark matter. The assumption that gravity alone is responsible for the motion of gas beyond the...
  27. A

    MHB Multiple choice question about electric fields and magnetic fields

    Consider a region where a 25-volt-per-meter electric field and a 15-millitesla magnetic field exist and are along the same direction. If the electron is in the said region, is moving at a direction 20 degrees counter-clockwise from the direction of the magnetic field, and is experiencing a total...
  28. H

    How closely do the magnetic fields generated by geodynamos align?

    Here on Earth there are three major geodynamos that generate the magnetic field. My question is about how they interact. My guess that while the axis of rotation of each field is different, the fields they generate tend to align. My further guess is that they do so only partially so that in...
  29. N

    Exploring Magnetic Fields: Is the Plate Affecting My Magnet?

    Hello all!, first post here we go! I was hoping someone could answer a question for me because I can’t find the answer online. Or maybe point me to a magnetic field’s for dummies website.. I’ve been playing with a neodymium magnet shaped like a coin for a few days (yes easily occupied) and...
  30. Shreya

    Plasma Experiment Involving Magnetic Fields

    I want to perform an experiment to show that magnetic fields can control plasma. (Can even be a slight repulsion) Please Suggest one. I have no idea where I can obtain plasma - I have access to candle flame (though it's not a proper plasma) & fluorescent lights. I have a permanent magnet (not a...
  31. U

    Trying to understand electric and magnetic fields as 4-vectors

    I was trying to show that the field transformation equations do hold when considering electric and magnetic fields as 4-vectors. To start off, I obtained the temporal and spatial components of ##E^{\alpha}## and ##B^{\alpha}##. The expressions are obtained from the following equations...
  32. L

    Electromagnetic effects and Magnetic Fields Questions

    1. When two parallel wires carry current in the same direction, they exert equal and opposite attractive forces on each other. 2. ε=lvBsinθ ε=0.02*5*0.1*sin30 ε=0.005 V 3. Well, a conductor moving through a magnetic field has the potential to induce an emf, but this movement must be in such a...
  33. haruspex

    Can magnetic fields do positive work in certain circumstances?

    Are you saying there are circumstances in which the work done in a magnetic field depends on the path taken?
  34. M

    Two nested solenoids and their magnetic fields

    a) is pretty clear and got correct but b) I'm struggling with. For b) I guess one could take the derivative of I and specify the moment t when you can plug that into Faraday's law. Or could this be solved somehow with inductance?
  35. V

    Relationship between electric and magnetic fields

    So, basically I can follow the math deriving E/B = c from Maxwell. And I can calculate B and H from I: H = I/2*pi*r and B=uH. Easy. So, for example I take a 2000 A, 50 Hz, current and a distance of 2 meter from that current in a round conductor. H and B are set: H = 160 A/m and B = 0,2 mT...
  36. F

    Lorentz transformations for electric and magnetic fields

    Good evening, I'm trying to solve this exercise that apparently seems trivial, but I wouldn't want to make mistakes, just trivial. Proceeding with the first point I wonder if my approach can be correct in describing this situation. From the assumptions, the two fields are in this...
  37. C

    Is the Configuration of Magnetic Fields Only a Convention?

    If I understand correctly, the concept of electric and magnetic fields originated with Faraday and was developed by reconceptualizing forces acting at-a-distance. For example, the electric field concept was developed by looking at the force on a test charge in the presence of a source charge...
  38. Epsilon Eridani

    Hypothetical discussion on the effect of magnetic fields on planets

    Ok, so I have long been fascinated with magnetic fields and their mysterious nature. I've been wondering what would happen when the magnetic field of Earth gets bent/disturbed/rippled by some extraneous force. I am aware the extent of effects that magnetic fields have on a planet is great, but I...
  39. jaumzaum

    B Is diamagnetism only present with varying magnetic fields?

    Hello. I was wondering if diamagnetic materials only repel varying electric field? By Ampere law only a variable flux can cause an electromotive force, so, and by what I understood diamagnetism is explained exclusively by Ampere law. Am I wrong?
  40. G

    Confusion on the magnitude of magnetic fields

    Here, the correct options are A,D. Solution: I got A as answer as ∫ B.dl=µI. But, the answer to the question says that it is a solenoid and therefore Bx=0 for point P. Here I'm a bit confused. I know this system resembles a solenoid in some ways, then By must have some finite value, but...
  41. A

    Magnetic fields generated by the general rotations of a charged rigid body

    The calculations for the magnetic field produced by a uniformly rotating charged sphere can be found in basically every book on electrodynamics. I wonder what happen with the magnetic fields produced by rotating rigid solid that also present precession and nutation movements. The question comes...
  42. V

    Motion of a Proton in Electric and Magnetic Fields

    a) 248*10^3 eV for 248kV Calculate the energy in J K=248*10^3*1.6*10^-19 =396.8*10^-19 J b) K=(1/2)mv^2 v=sqrt(2k/m) =sqrt((2*396.8*10^-19)/1.67*10^-27) =218^10^3 m/s c) r=mv/qB =1.67*10^-27*218*10^3/1.6*10^-19*1.5*10^-4 =15.17 mr=mv/qB...
  43. J

    Magnetic Fields & Forces on Conductors

    Hi, Here is a multiple choice question I am stuck with and would appreciate some guidance: The mark scheme for this paper says it is option A - 0N. I didn't get that at all. If a current carrying wire is in a magnetic field with some component perpendicular to the field then how can it be...
  44. SianRR

    Motion in Electric and Magnetic Fields -- (Uni Level Dynamics)

    I've attached my attempt at a solution below, I thought integrating it would be the best way to go but I'm just getting so confused and could use some help. This isn't my first attempt at a solution either I've been working on this for just under two hours now.
  45. Adesh

    Can a magnetic field ever cause a translation motion?

    Lorentz Law says that for a charged particle moving with a velocity v in a magnetic field B then the force on it is given by $$ \mathbf{F} = q (\mathbf{v} \times \mathbf{B}) $$ Now, if I say that particle’s velocity and the magnetic field are aligned then according to Lorentz Law there will be...
  46. M

    Moving electron under two magnetic fields

    In this question, I would have to calculate the force in respect to time. However, the question gives me the value of the mass of the electron. In my attempt, I didn't take that into account. I just replaced ##v## with ##\frac{d}{t}## and made the Lorentz force undergone by the particle...
  47. jisbon

    How are the angles involved in deriving magnetic fields for a current loop?

    So I have managed to derive the magnetic field of a current carrying wire, however, I seem to have some enquiries on deriving the one for the loop. In the formula where ##\frac {ds * r} {r^2}##, I know that it will become ##ds sin \theta.## However compared to the theta in the wire, the theta...
  48. R

    Fluctuating Magnets: A Guide to Interacting Magnetic Fields

    How would it be possible to fluctuate one magnet between two magnets? Thanks