Magnet Definition and 912 Threads

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.
A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.
An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.

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  1. Einstein44

    I Calculating Magnetic field strength of a magnet

    I have been trying to calculate the magnetic flux thought a single loop of wire occurring from a magnet (meaning it has a nonuniform field), so I have the following equation: Φ=∮BdAcosθ Now my problem is that I do not know how to calculate the magnetic field strength (B)of that magnet (which...
  2. V

    Swinging a hanging copper ring with a bar magnet

    I thought of few scenarios and they ended up as follows: The ring must have an induced current. Due to the symmetry of the ring, if one part of the ring feels a force, the part of the ring radially opposite this part will feel a force opposite in direction, since the current will be opposite in...
  3. T

    How distance affects the impact of magnet collision

    Hi, I'm studying how distance affects the impact of magnet collision. Would like to have some idea before conducting experiment. Imagine 1. holding a magnet at different distance near a fixed metal 2. release the magnet; the magnet attract and collide to the fixed metal Will the distance affect...
  4. H

    Force on a charge centered around a rotating magnet

    Charge will experience a rotating magnetic field around it. What will be electric field ( If any ) at the centre, generated by rotation of magnet ?
  5. 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...
  6. cel123456

    Magnet repulsive force -- how long does it last?

    As we know the magnet will stop to repel each other after some time, is there any formulae to calculate when it will stop? From common sense, how long magnet will stop repel each other? 1years?
  7. M

    Bar magnet made from smaller opposing bar magnets

    I was wondering if the strength of a bar magnet constructed from smaller magnets would increase if the smaller magnets were placed in an arrangement where the poles were opposing each other. I was able to jam 2 rare Earth magnets together with opposing poles and measured a higher magnetic flux...
  8. Z

    EMF induced by a magnet falling through a coil

    I've been told that if you drop a magnet through a coil the induced emf and flux graphs would look like this: I understand that when the bar magnet is in the middle of the coil the emf induced is zero as flux change in top and bottom is in opposite directions but why is effective flux maximum...
  9. A

    PPMT, Magnetic Flux Switch, electro-permanent magnet generator

    Ok so here is something that made me scratch my head and I still can't come to a final conclusion. The basic idea is seemingly simple. You have permanent magnets attached to a core, the field lines close on both magnets through the core, so far so good. but the core also has electromagnets , put...
  10. G

    Demagnetizing Magnets: Alternating & Direct Currents

    Is it possible to demagnetize a magnet using alternating current? How does this happen? And is direct current also possible?
  11. C

    Which of these magnets should have the strongest strength at 10cm?

    Basically, I need to generate the strongest possible field at 10 cm from a circular magnet, in its central axis. I hesitate about what buying. For example, the following magnet has a large diameter of 90mm and is flat, with a suction of 250 kg. This other magnet has a smaller diameter of...
  12. N

    Magnet falling thru copper tube -- How does the process occur visually?

  13. Steven Ellet

    Can a horseshoe magnet without separated poles still function as a magnet?

    If you take a horseshoe magnet and fuse the north and South Poles together (without destroying the magnetic field) would you have a “pole-less” magnet? And if so, what special properties would it have(other than other magnets)?
  14. Gonzalo Lopez

    Motion Equation for a magnet on a spring

    Apart from the trivial elements of the motion equation (m z'' = -kz -mg), I am required to find the force produced by the Eddy currents induced by the moving magnet. To do so, I calculated the magnetic flux through the hole plate: For a magnet: Bz=μo m 4π. 2z^2−r^2/(z^2+r^2)^5/2 so Φ = a→ +∞...
  15. Despot

    Which of the 2 metals is the magnet

    No idea where to start
  16. entropy1

    I Ontology of an electron passing through a Stern-Gerlach magnet

    So, as far as I think I understand, an electron that passes through a Stern-Gerlach magnet, will not have a value for its spin until that spin is measured? Does that mean the electron has no position (as given by the SGM) until measured, or that the electron does not even exist until measured?
  17. danielhaish

    Magnetic Attraction: Watching Magnets Move in Unison

    so I toke three magnet, two smell magnet and big one so the big one is attractive both of small onces so it order like -(+-)+ . I toke the small magnet close to the edge of the range magnetic and lift it so the magnetic field is preventing it from falling because the magnet is trying to flip...
  18. H

    Deflection of a Magnet in an Inhomogenous Magnetic Field

    Say I've got a magnet flying through empty space in a homogenous magnetic field. The magnet precesses and flies in a straight path. Now make that magnetic field inhomogenous. The magnet precesses and flies in a curved path. What I can't figure out is why the path is curved. It is because...
  19. G

    How do you calculate power from a magnet in a coil?

    I don't really know but if I were to guess it would be based on how many turns are in the coil, the diameter of the coil and the flux of the magnet. Unfortunately I couldn't find a formula anywhere.
  20. gmax137

    Jeopardy "Magnet" question - hard or easy?

    I was watching Jeopardy last night. In the Category "Magnet" was the following: "An 1845 letter from the 21-year-old future Lord Kelvin inspired this British scientist to show how magnetism & light are related" My guess: I was pretty sure this was wrong, based on the 1845 time frame, but I...
  21. 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...
  22. C

    Reluctance of a bar magnet circuit?

    If you hold a bar magnet in the middle of an empty volume and put a gauss meter in front of a pole, there is evidently a measurable magnetic flux, so there is a magnetic circuit there. What is the reluctance of the whole circuit, not counting the bar magnet itself? How do you work that out? Is...
  23. rayjbryant

    Calculating the terminal velocity of a magnet falling through a copper coil

    The magnet being used % magnet dimensions [m] d = .0127; r = .00238; %mass of magnet [kg] m_w = .0017; % other constants u_0 = 1.26E-6; % permeability of free space constant T m/A g = 9.81; % gravitational constant in/s^2 %coil properties [22 gauge wire] [m] a = .00635; %radius w =...
  24. T

    Vector field equality Curl Proof of Moving Magnet & Conductor Problem

    The moving magnet and conductor problem is an intriguing early 20th century electromagnetics scenario famously cited by Einstein in his seminal 1905 special relativity paper. In the magnet's frame, there's the vector field (v × B), the velocity of the ring conductor crossed with the B-field of...
  25. A

    When is the flux through a coil from a bar magnet zero?

    Suppose I have a finite sized cylindrical bar magnet of radius $a$ and length $b$. It is coaxial with the $x$ axis and moving from $-\infty$ to $\infty.$ A circular closed wire of radius $r>a$ is in the $y-z$ plane with center at the origin. When the bar center of the bar magnet passes through...
  26. Curious_Student

    Mechanics Lab | A Simple Pendulum & a Small Magnet Underneath

    I have measurements of period time and distances that's all: T (sec) D (m) 0.9 0.008 0.91 0.009 0.97 0.01 0.98 0.011 1.06 0.012 I thought about adding the magnetic force like: T=2π*√l/(g+x) but have no clue how to integrate the distance there, I don't know even how to start...
  27. George-M

    Best permanent magnet arrangement?

    If I have a block of N52 and I want to make it's magnetic field as strong as possible, would a Halbach array give me this maximum or is there a different pole arrangement/array that would provide this? I'm thinking for the use in a motor, so the field doesn't have to be large. A close field...
  28. danielhaish

    Does the size of a magnet affect its range?

    I wandering if the size of magnet or if there is vacuum or not change the range of magnet
  29. Fdtroya

    Which factors determine the power output of a permanent magnet alternator

    To be more precise the generator has to be able to produce around 1.5 Watts from a person spinning its axis, which is why I was thinking of putting a gearbox in my design but I need to know how much Torque would it take to spin the axis and at what rpm would the generator be effective.
  30. Nonametheone

    What are the rules for asking questions on mainstream science and math topics?

    I am a real person. I ll do my best not to ask dumb duplicate questions.
  31. P

    Measuring Magnetic Field Strength of a Cylindrical Magnet

    Hello, Today I am wondering if anyone can help me quantify the strength of the magnetic field created by a permanent cylindrical magnet. I have been able to find equations online for the strength of the field within the z axis, (ie. the longitudinal length) but I would like to know the strength...
  32. C

    EMF induced in an off-axis solenoid due to a rotating magnet

    The red arrows correspond to the areas the solenoid will be moved too
  33. N

    Formula to calculate the pull force between a magnet and a steel plate

    i have a neobydium magnet of grade n40 , the diameter of magnet is 15mm and thickness is 10 mm , now i want to calculate the pull force between this magnet and a steel plate when there is no gap between them ; & in second case i want to calculate the pull force when i put a 0.15mm copper plate...
  34. S_Wildjocks

    Forces acting on a magnet which is deflecting a charged particle

    Summary: Considering a charged particle moving through a magnetic field, what forces does the particle exert on the magnet that is causing it to deflect? Hi all, probably a dumb question, but what force(s) does a charged particle exert on a magnet as it passes through it's magnetic field and...
  35. Quix270

    Magnet pole question in generation

    What would happen if a coil it’s exposed to a moving magnetic field with only north poles? Coils being exposed to only North Pole. Will produce alternate current or nothing?
  36. H

    If a magnet does not feel the Lenz force, will there be a violation of energy?

    Consider the following, a magnet and a charge is attached to a platform, which is constrained to move only up and down direction. Now, if magnet is moved towards charge, due to changing magnetic field, an electric field will be created. This electric field will impart force on charge. since the...
  37. George-M

    Number of Turns vs. Wire Gauge (BLDC Motor)

    Summary: For the same mass of copper wire, would more turns or greater thickness create a stronger magnetic field from a coil? So I am attempting to make a brush less DC motor, and I am wondering whether the coils would create a greater magnetic force if there are more turns or if the wire is...
  38. M

    Effects of a static magnet on a pulsed electromagnetic field?

    Summary: Does a static magnetic field affect a weaker pulsed magnetic field close by? If you have a static magnet close to a low level pulsed electromagnetic field, will the static magnetic field influence the pulsed field if the static magnetic field is the same strength or stronger than the...
  39. H

    Larmor Precession and a bar magnet

    As stated in the link below, when a magnet bar (or a current loop) is placed in an external magnetic field it (its magnetic moment) becomes aligned with the magnetic field while an orbiting electron would have precession with Larmor frequency. What is the reason for these different behaviors...
  40. H

    I A bar magnet and magnetic moment in a magnetic field

    Why a magnet bar would become aligned with the external magnetic field while a magnetic moment would precess around the external magnetic field?
  41. Christoffer B

    Imperfections in magnet pole pieces

    Hi all, I'm fairly new here. I'm currently designing an as-homogene-as-possible permanent magnet for low-field NMR and similar experiments. I'm on a fairly tight budget, and having finally found pole pieces for my magnets, I got them even though they have a small saw cut in the edge. approx. 5...
  42. I

    Why does a magnet above a superconductor stop spinning?

    I got the opportunity a while ago to play around with a magnet floating above a superconductor cooled with liquid Nitrogen. The magnet was a little cube, and I spun it with a pair of tweezers. I was surprised at how quickly it stopped spinning, it seemed to stop much quicker than could be...
  43. M

    Electromagnet that can generate 100 lbs at small size

    I wondering if it is possible to create an electromagnet that has a diameter of 0.5 cm that can generate 75 - 100 lbs of pull force. I took physics in college so I have a basic understanding of how magnets work, but I don't have any practical knowledge. I don't know what is feasible. I found...
  44. S

    Can a magnet bend a ray of light?

    Can an everyday magnet disturb a ray of light. I have seen many answers online saying no, and some saying yes, but only if the magnetic field is large enough.
  45. TheBigDig

    Force on a magnet in a magnetic field

    So I'm kinda stumped. I'm assuming that since ##\vec{m}||\vec{B}##, the x and y components of both are zero. But I'm unsure how to take this further.
  46. W

    The direction of magnet field

    for a infinite length length of current, only consider a part of it, is the direction of magnet field of a ring on the mid vertical plane the same magnitude and along the tangential direction? and for a closed surface , if the flux is 0?
  47. S

    Ansys Maxwell -- How do I add a permanent magnet into my simulation?

    hi all I am going to do a project in ansys maxwel, actually i need to add a magnet and i know i have to do it with add material. my magnet is NdFeB . i give the material from net, actually i can not valid them because they are different in value. I need to calculate Mu(permeability ) and I nedd...
  48. chemisthypnos

    Is neodymium powder as strong of a magnet as solid neodymium

    In attempting to make magnetized neodymium powder, I grinded neodymium magnets into a powderusing a belt sander. However, I found that the magnetic properties of the neodymium had decreased substantially. It would appear that any attempt to grind the magnets into a powder using this method seems...
  49. Z

    If a magnet could switch, could it attract and repel?

    Hello the first image with the letters going ABCD is picture #1 and then BACD is picture #2 for references. Tools: - Normal magnet. Nothing special about them. - And we will say they have some type of system where they do not move sideways. Only up and down and have a difference of 5 cm when...
  50. T

    What's the derivation in a moving magnet & conductor problem?

    In the Wikipedia page of the moving magnet and conductor problem, it asserts "This results in: E' = v x B", but does not elaborate why. What's the full derivation?
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