What is Magnetism: Definition and 970 Discussions

Magnetism is a class of physical attributes that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomenon of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. The rare-earth metals neodymium and samarium are less common examples. The prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4.
All substances exhibit some type of magnetism. Magnetic materials are classified according to their bulk susceptibility. Ferromagnetism is responsible for most of the effects of magnetism encountered in everyday life, but there are actually several types of magnetism. Paramagnetic substances, such as aluminum and oxygen, are weakly attracted to an applied magnetic field; diamagnetic substances, such as copper and carbon, are weakly repelled; while antiferromagnetic materials, such as chromium and spin glasses, have a more complex relationship with a magnetic field. The force of a magnet on paramagnetic, diamagnetic, and antiferromagnetic materials is usually too weak to be felt and can be detected only by laboratory instruments, so in everyday life, these substances are often described as non-magnetic.
The magnetic state (or magnetic phase) of a material depends on temperature, pressure, and the applied magnetic field. A material may exhibit more than one form of magnetism as these variables change.
The strength of a magnetic field almost always decreases with distance, though the exact mathematical relationship between strength and distance varies. Different configurations of magnetic moments and electric currents can result in complicated magnetic fields.
Only magnetic dipoles have been observed, although some theories predict the existence of magnetic monopoles.

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  1. J

    I Question about Activating Solenoids that are facing each other

    In this situation I would have two solenoids facing each other, such that both ends are north for example, and when activated they are actively experiencing repulsion, I know that the magnetic field of both would decrease in strength, but would there be any affect on the electrical input of each...
  2. S

    I qv x B force in electron's proper frame

    Can we describe / explain the B x v force in the electron's own reference frame without reference to relativistic invariants, 4-vectors, tensors et al? The aim would be to explain things like the following video without the notion of "field lines" that electrons and wires move through. But the...
  3. G

    I Force between opposing magnets

    Following a conversation with @Tom.G , I’ve come up with the following question, to which we’d both like an answer: Imagine two drilled magnets threaded onto a frictionless upright shaft, set N-N. One fixed down, the other floating above. Now, if I move an iron gate in and out of the gap (the...
  4. M

    Do Magnetic properties change?

    Hi Quick question related to magnetism If I have a magnetic core and place that core onto a magnet, then roll the core on a flat surface ( whilst its still on the magnet), does that increase the permeability and magnetic field of that core ? If so, what is the theory behind that. thank you in...
  5. amoghthebad

    (Magnetism) Magnetic pull force on a steel ball

    I have to write a physics research project, and the topic I chose is magnetism. More specifically, the relationship between the final velocity of a steel ball, and the magnetic field strength in a gauss cannon. However, for the part where I use mathematical formulas to predict the results...
  6. D

    A confused Compass Needle between two solenoids

    Original Question: If a small magnetic compass needle was placed at point Z, what direction would its north pole point? Explain your answer My try: Since the current flowed in an anticlockwise loop in the first wire => North pole was formed inside the loop => Outside the wire near the point...
  7. jaketodd

    I Effects of magnetism on spacetime curvature, and implications

    Quotes from Cosmic magnetism, curvature and the expansion dynamics: "Most interestingly, the coupling between magnetism and geometry implies that even weak fields have a significant impact if the curvature contribution is strong." "The energy scales involved vary from ∼ 100 MeV at the QCD...
  8. Hak

    I What causes the magnetic force in a uniform magnetic field?

    As is well known, when electric current flows in a straight wire, a charge in motion in the vicinity of the wire, parallel to it, is affected by a force called the magnetic force, which is attributable to the relativistic contraction effects that the wire undergoes in the frame of reference of...
  9. doomer

    I Geometry of Magnetic field lines as they approach a magnet pole?

    Magnetic field lines are loops, so at the surface of a magnet (axially magnetized) cylinder) pole they look like this? there is a dead zone at the center where there is no lines/magnetic field present? or perhaps they look more like this? lines converge in the middle to a single line or point...
  10. Leureka

    I Magnetic field as result of length contraction

    Hi all, Recently I've tried to wrap my head around a common explanation of magnetic fields that you see online, especially among science educators like veritasium or minute physics. The setup is as follows: there is a wire, composed of the same number of negative charges (electrons) and...
  11. Y

    Diamagnetism confusion -- Does diamagnetism really have to do with Lenz’s law?

    In my textbook, and on many websites it says that when placed in a magnetic field and then due to Lenz’s law a magnetic dipole moment is created in atoms and so the material gets attracted to the magnet? But then in the case I bring the magnet close to the material very slowly( so the change in...
  12. Frigorifico9

    I Is my interpretation of the g-factor correct?

    I'm trying to make sure I understand the g-factor of the electron, so if my question is flawed please don't just point out my flaws, but help me correct my understanding If I understand correctly the magnetic moment of an object depends on it charge, its mass and its momentum $$ \mu =...
  13. P

    Intro Physics Looking for a book that can help with conceptual understanding of elctromagnetism and electro magnetic devices

    So my neighbor is interested in electricity and magnetism. Well he's actually been watching youtube videos and thinks he can make some kind of free energy device. But anyways I thought it could be fun to do some real projects with him like playing with magnets, making a diy DC generator, and...
  14. jaketodd

    B Any limit on how fast a Maglev can go?

    When using magnetism to accelerate the Maglev, and neglecting the usual frictions, and also relativistic effects, is there any limit how fast it can accelerate to? Or is there any sort of increasing "drag" of any sort native to magnetism, which would get in the way of acceleration, as it goes...
  15. casparov

    Calculate the Magnetic Vector Potential of a circular loop carrying a current

    Can someone explain what exactly happens at (4) ? I do not clearly follow, except that there is some cosine law going on? I also do not really understand why at (3), r' doesnt have a z hat component, but I can live with that.
  16. S

    I Can Conducting Current Through a Bar Magnet Cause Movement?

    Following the Picture below, If I Conduct current through Permanent magnet Bar and hold the battery still. Will the magnet move in any direction ? Thank you.
  17. H

    I Magnetism: Same Pole Repulsion & Heteropolar Attraction

    We know that the two magnets have same-pole repulsion and heteropolar attraction; In most parts of the planet, a magnet is hoisted with a thin wire, one side of the magnet will point to the guide, and the other side will point to the north; If you come to the magnetic pole of the earth and place...
  18. 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.
  19. Lotto

    How to calculate magnetic induction just beyond the end of the magnet?

    I know I should use a limit $$B=\lim_{r\to l}{\frac{\mu}{4\pi}\cdot \frac{4rml}{{\left({r}^2-l^2\right)}^2}},$$,but in Wolfram I get a weird solution. https://www.wolframalpha.com/input?i2d=true&i=Limit[Divide[4rl,Power[\(40)Power[r,2]-Power[l,2]\(41),2]],r->l] What is the solution? It...
  20. vdance

    How are the poles of a tapered magnet distributed?

    How are the poles of a tapered magnet distributed? Is there any way to calculate its magnetic force?
  21. V

    Why are the effects of a magnetized material neglected in this case?

    According to what I know, the net magnetic field ##\vec B## inside a solenoid is given by $$\vec B = \mu_0 \vec H + \mu_0 \vec I$$ where ##\vec B## is the net magnetic field inside a current carrying solenoid, ##\vec H## is the magnetic intensity ( aka magnetic intensity or magnetizing field...
  22. V

    Why does a diamagnetic rod align perpendicular to a magnetic field?

    I know that each material is made up of tiny magnets due to electrons orbiting the nucleus and also from electron spinning about its own axis. In ferromagnetic or paramagnetic rod these tiny magnets align with the applied field causing the net field in the rod to increase. But for diamagnetic...
  23. X

    I Magnetic field strength of a stack of magnets

    I know that for a single cylindrical neodymium magnet, the formula $$ \displaystyle{\displaylines{B(z)=\frac{μ_0M}{2}(\frac{z}{\sqrt{z^{2}+R^{2}}}-\frac{z-L}{\sqrt{(z-L)^{2}-R^{2}}})}} $$ shows the relationship between the magnetic field strength and the distance between the magnet. I was...
  24. B

    Velocity of a relativistic particle in a uniform magnetic field

    d(ɣmv)/dt = qvB (dɣ/dt)mv + ɣm(dv/dt) = qvB Substituting gamma in and using the chain rule, it ends up simplifying to the following: ɣ^3*m(dv/dt) = qvB Now, I am confused on how to solve for v.
  25. dliu1004

    B Questions regarding Magnetorheological fluids

    Hello, has anyone worked with magnetorheological fluids before? I plan on creating one for a project by using carbonyl iron powder, a surfactant, and some oil. I have heard that when subject to a current, these liquids basically become solids. However, I am not sure if they become complete...
  26. Rzbs

    I What makes cobalt oxide (co3o4) a magnetic material?

    We know cobalt is a magnetic material, it can attracted by magnet. Now if we want to know for example cobalt oxide (co3o4) has magnetic property or not what we should do? I mean is there a role to know bonding of cobalt with which elements results in magnetic property? or is there any online...
  27. GiuliettaL

    I with my quantum magnetism paper

    (I have to write a 1500 word essay briefly explaining quantum magnetism. But i am having a hard time structuring my essay as I need to select what is crucial and what is not since 1500 words is not a lot. is there anyone with any input for me? Ideas, recommendations, sources anything is...
  28. Boltzman Oscillation

    I How does the magnetic component of an EM wave affect surroundings?

    Hi all, as we all know EM waves are made up of magnetic and electric waves in a plane perpendicular to the direction of propagation. Given this, why don't I see conductors being affected when I shine light at them? Woulnt the magnetism cause a force? Is is that the force is too small? What am i...
  29. angweieng

    A Definition of finite size, radiative and weak magnetism corrections

    Hi all, I would like to understand the definition of finite size correction, radiative correction and weak magnetism correction, with their impacts on the beta spectrum. I'm not a physics student, thus I would like to seek for a help about the simple explanation that can be understand by...
  30. S

    Magnetism / Electromagnet Levitation question

    I can make one magnet ‘leap’ up to another magnet and I can push one magnet away with another magnet but can’t figure out how to do both at the same time so the first magnet can essentially be suspended in mid air with the controlling magnet being above. Any thoughts are appreciated. Thanks
  31. samy4408

    I Positive Charges: Explaining Motion Despite Net Force = 0

    in a cours of electrostatic when we have a positive charge and we bring another one (also postitive)we have to do work and apply a force that equals the force of repultion over the distance which seems weird because if we do that the net force will be equal to 0 and the charge will not move can...
  32. A

    Trajectory of an electron traveling near a current-carrying wire

    B equals 50*10^-7 T (at first instance) Fm equals 8*10^-20 N (at first instance) I know Fm is perpendicular to the velocity, and I know the estimation of the trajectory (somewhat similar to the curve y=lnx). Since I think vertical velocity will be constant, only changing the x component, I...
  33. cellist542

    Hardest content to learn for AP Physics C: Electricity & Magnetism

    What are some of the hardest concepts to learn in AP E&M? I am going to prepare for the exam with my previous physics teacher. I am currently a senior enrolled in AP Calc BC, and I already took AP Mechanics.
  34. Anmoldeep

    I Work Done in Changing Shape of Current Carrying Loop

    How would you go about calculating the work done in morphing a square current-carrying loop into a circular current-carrying loop, without change in length while maintaining the same angular orientation with an external magnetic field. My book suggests defining P(potential energy) = M.B (dot...
  35. C

    B Conservation of energy and magnetism

    Please redirect me to the correct part of thr forum if this is the wrong place When we lift up an object n then let it fall back, then potential energy - > kinetic energy If I drop a magnet onto another magnet with like pole facing each other (that sits on the floor), the falling one maybe...
  36. Viona

    Spin-Orbit Coupling in Hydrogen Atom: Understanding the Calculation

    I was reading in the Book: Introduction to Quantum Mechanics by David J. Griffiths. In chapter Time-independent Perturbation Theory, Section: Spin -Orbit Coupling. I understood that the spin–orbit coupling in Hydrogen atom arises from the interaction between the electron’s spin magnetic moment...
  37. V

    Engineering What is the magnetic field of a half toroid?

    Hello, I would like to know what is the magnetic field of a half toroid. Would we use Ampere's law? So, considering that the integral is equal to BA, we would have BA = μo * i, then B = (μo * i) / r. But, using Biot-Savart's law, by symmetry, it seems that the vector sum of all the...
  38. N

    B Why do moving charged particles feel a force in a magnetic field?

    When I read things about magnetism on internet, I don't understand at all about one thing: If a moving particle receive a force if it's in a magnetic field, so it should accelerate, so what happen if we change the referential so that the particle now don't move? The particle shouldn't receive...
  39. D

    Can any object cause fluctuations in a magnetic field?

    Summary:: Can a moving object cause disruptions in a magnetic field that could be detectable? Hello, I was hoping someone could assist me on a query I have regarding disruptions in a magnetic field. For some context, I am creating a science fiction story which features a non-humanoid alien...
  40. S

    I Magnetism and Gravity Discussion/Questions

    Hi all, I've recently become transfixed with the idea of magnetism and gravity. I have two main questions I'd like to see discussed more. 1. Would it be possible to harness magnetic fields for energy on earth/for acceleration between planets? 1a. Has this been studied at all? 2. Why do we...
  41. P

    EM fields and Current between 2 charged cylinders

    The task is to find the magnetic field between the 2 long cylinders, which extend to infinity. Integration is involved to find the total current passing through the Amperian Loop shown below. What I do not understand is why only sides 1 and 3 contribute to that B ds part of Ampere's Law. Isn't...
  42. Ale_Rodo

    "Barlow's wheel" used as an electrical generator

    In this thread, I hope to find some help in understanding one of the first application of Faraday's law of induction: the "Barlow's wheel". Basically the machine converts electrical power to mechanical, so as you can imagine, a battery, some conductor wires, a horseshoe magnet and a metal wheel...
  43. P

    Why is magnetic field half at the sides of a solenoid?

    For a solenoid, magnetic field at the centre = ##\mu_0nI##. I see the argument on why at the opening at the ends of the solenoid, the B-field is ##\frac12\mu_0nI##. Apparently, B-field is ##\frac12 \mu_0nI## at the sides of the solenoid too. (ie at/within the wires that make up the solenoid)...
  44. P

    Qualitative explanation of Magnetic Braking

    When a magnet moves near a non-magnetic conductor such as copper and aluminium, it experiences a dissipative force called magnetic braking force. I am rather confused by the following explanation of magnetic braking force: The non-magnetic conductor here is the aluminium 'wall' seen on the...
  45. P

    Ampere's Law for a toroid (finding relative permeability of iron)

    Why is this equation: B(D - d)/mu + Bd = mu0 N I true? B = magnetic field in the hole of the toroid D = Average diameter of the toroid d = Diameter of hole of toroid mu = relative permeability of iron, or whatever the toroid is made of mu0 = 4pi x 10^-7 N = Number of turns on the toroid I =...
  46. H

    Finding Magnetic Field of a Toroid with Two Circuits

    I have a toroid with square cross section and 2 different circuit: ##C_1## where ##N=N_1## and ##I=I_1## ##C_2## where ##N=N_2## and ##I=I_2## I have a question that say I have to find the magnetic field ##B## produce by ##C_1## everywhere inside the coil. I assume here I have to find the...
  47. G

    How do metal balls induce stability in a tetrahedral magnet arrangement?

    Hi...take six regular N/S rod magnets and arrange them as a tetrahedron. It's fiddly to achieve...because it can't actually be done in terms of magnetic attraction/repulsion. Each of the four vertices have 3 poles meeting & in each case the situation in one whereby one pole is attracted to the...
  48. P

    Stewart-Tolman Effect (Current caused by Acceleration of wires)

    Consider the inertial reference frame in which the positive ions forming the crystal lattice of some portion of a metallic ring are at rest. In this frame, an inertial force of mra exists. Consider the electrons in this portion of the metallic ring. The inertial force of mra is exerted on the...