What is Magnets: Definition and 562 Discussions

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. T

    Breaking Filaments using magnets.

    Homework Statement Bringing a strong magnet close to an operating incandescent light bulb has the effect of breaking the filament. Breakage might be expected when the extra force on the filament becomes comparable with gravity. Estimate the field strength likely to cause problems with a...
  2. O

    Relationship between initial speed of cart and distance repelled by magnets.

    1. Determining the relationship between initial speed of a cart (with magnets, aligned with and moving towards magnets on a wall) and the stopping distance from the wall) 2. Kinetic energy(Ke)=Magnetic potential energy(Mpe) Ke=mv^2/2 Mpe=km1m2/r mv^2/2=km1m2/r...
  3. T

    Time constant and pulse magnets

    Greetings I've been reading about these magnets such as these: http://www.lanl.gov/orgs/mpa/nhmfl/magnets.shtml Take a look at the pulse durations (it says in notes at the bottom "Total pulse length including decay" It's all nice but I don't understand one thing. How can they make...
  4. E

    Levitation with Permanent magnets

    Hi everyone, I've been trying to find info about getting an object to levitate and how strong the magnets need to be but haven't had much luck. I'm trying to build a levitating picure frame using permanent magnets rather electromagnets. The plan was to take apart a lamp and put in two ring...
  5. P

    Electricity, Magnets, & Circuits

    Homework Statement Part A- Charges and Fields 1. Click on the category named Electricity, Magnets, & Circuits, then find Charges and Fields, click on it, then select Run Now!. (You may need to install Java onto your computer) 2. Select Grid and Show Numbers in the green menu box. Place equal...
  6. N

    Magnitude Of Force Between Magnets

    It is my understanding that the force between magnets relates directly to the shape of each magnet. To annul the shape of the magnet, I am seeking a formula that describes the force between two magnets in terms of magnetic flux density. My Question. If two permanent magnets faced each...
  7. madmike159

    Where do magnets get their energy from?

    Since everything has to obey the law of conservation of energy, where do magnets get their energy from? They can lift something up through a gravitational field which requires energy. If the energy for a solid state magnet comes when you magnetize it (e.g. moving it with your hands with another...
  8. E

    Maximizing Magnetic Pull for Object with 2 Halves: Cylindrical vs Ring Magnets"

    I figured with how big the internet is, there would be an entire forum on magnets somewhere out there for me to ask my question but it turns out, if it does exist, I couldn't find it. So I figured you guys would be just as good, if not better :smile: I'm building an object that has 2 halves...
  9. G

    Work with Magnets: Generate Energy from Magnetic Force

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  10. K

    How Does Lenz's Law Determine Current Direction in Moving Loops and Magnets?

    Homework Statement The figures below show two different situations where a current may be induced in a loop according to Faraday's Law, with the direction given by Lenz' Law. The magnetic field is shown by the x's in Fig. 2. Select ALL correct answers (i.e. B, AC, BCD) for the current in the...
  11. Z

    Maglev Train by 10 kilometer Permanent magnets

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  12. Astronuc

    Magnets and Magnetic Particle Inspection

    Magnetic Materials - http://www.aacg.bham.ac.uk/magnetic_materials/ Table of Contents History of Magnetic Materials Origin of Magnetism Magnetic Units & Terminology Classification of Magnetic Materials Intrinsic Properties of Magnetic Materials Magnetic Domains Magnetic Hysteresis...
  13. N

    Harnessing Electricity from Magnets: Understanding the Impact of Polarity

    I have read in quite a few places that you can pass a wire through a magnetic field and this will produce electricity. Does the polarity of the magnet have any effect on this or is it just the fact that it is a magnetic field? To be a little more specific, if you had a wire setup next to an...
  14. P

    Making Magnets: Attracting & Repulsing - Questions Answered

    How are magnets made? I mean how are they made to produce a magnetic field? How are some magnets made to attract and some to repel? And just to know:- Does magnetism got some connection with gravity? Because practically we can notice some similarities.I think I am asking an answer to silly...
  15. B

    Force beteween two bar magnets

    Hi there. I got two questions for you: 1- How can I calculate the force of attraction in Newton of two bar magnets of about 5 cm long and 2 cm wide separated by a few centimentres? 2- If I want to reduce near to nothing the attraction of these two magnet (whil still kept at the same...
  16. E

    Magnetic Linear Accelerator ( finding magnets)

    So i have decided for my physics project to build a magnetic linear accelerator made with half inch ball bearings on a plastic track. The first bearing is rolled and accelerated by the magnet which when struck, launches the ball on the other side due to the momentum of the accelerated bearing...
  17. N

    Regarding Solenoid and Magnets

    Hello, I was doing some questions and I thought I was understanding solenoids and magnets in incorrect way.. The question was, what would you feel if you bring a magnet close to a solenoid. I've wrote 2 possibilities, first is that they will repel and the second is that the solenoid would...
  18. J

    Exploring Effects of Magnets on TV Screens

    Homework Statement A strong magnet is placed on the screen of a television set (permanently damaging the tube). Explain the following observations. a) the picture becomes distorted b) the screen is completely dark where the field is strongest Homework Equations none. The Attempt...
  19. Q

    Extending the range of electro magnets? Can it be done?

    Is it possible to extend the range of an electromagnet? How would one do this?
  20. Q

    What kind of damage will 800lb neodymium magnets do to electronics?

    I know this doesn't pertain so much to engineering but I figured you guys would know best. If you set the magnet next to a cell phone or TV, what kind of damage would be expected?
  21. M

    Force between two magnets as related to distance

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  22. K

    Science Challenge: Prove these magnets won't move

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  23. Q

    Neodymium Magnets: Does Size Matter?

    They pull a lot of pounds in ratio to their size, I was wondering if it would make any difference in the energy output if you replaced the normal magnet with a neodyniam.
  24. S

    How High Does Block m1 Rise After an Elastic Collision with m2?

    Homework Statement Two blocks are free to slide along a frictionless wooden track ABC as shown in Figure P9.20. The block of mass m1 = 5.02 kg is released from A. Protruding from its front end is the north pole of a strong magnet, repelling the north pole of an identical magnet embedded in the...
  25. E

    Magnets vibrating near a current?

    In school yesterday I was doing a practical and when I moved a small 1.5T block magnet near a rheostat the magnet started vibrating, why does it do this?
  26. E

    Exploring the Effects of Combining Small Magnets in a Cube or Sphere Shape

    If you combine many small magnets together in a cube or spherical shape (say those 1.5 tesla rare Earth magnets), is the resulting magnetic field able to affect even heavier objects, or is there no difference in the range/energy of the field?
  27. T

    How Long Can Magnets Maintain Their Properties in a Repelling Magnetic Field?

    Just a few simple questions about magnets: 1) If 2 permanent magnets are placed one on top of the other such that one magnet repels the other and therefore the second magnet levitates and assuming that this is a ideal situation and the magnet is not knocked off its vertical levitating...
  28. K

    Electromagnets and Permanent Magnets

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  29. F

    How does magnetism arise in permanent magnets?

    Hi everyone! As I understand it, magnetism can be explained by special relativity when charges are moving - length contraction in different frames of reference leads to coulomb forces between the charges in these frames. But how does magnetism in a permanent magnet arise? Are there...
  30. Q

    E&M Toroidal Magnets: B, H, M Magnitudes

    The magnetic field inm the gap of the toroidal permanent magnet is 0.50 T. The length of the magnetic circuit is 20 cm and that of the gap is 1.0 cm. what are the magnitudes of i) B in the material ii) H in the gap iii) H in the material iv) M in the material The Attempt at a Solution...
  31. D

    Something interesting about magnets and weighing scales

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  32. L

    Magnets (and other things) at the speed of light

    Magnets at the speed of light. I guess that if you propel a (natural) magnet close to the speed of light then nothing unusual happens to the magnetic field because it already exists and is accelerated along with the magnet, but what happens to an electro magnet? If an electro magnet is...
  33. F

    How To Calculate Position Two Magnets Will Attract And Lock

    Hi All, Do equations (or branch of study) exist for the following problem: I have two (or more sphere magnets); can it be determined mathematically/classical-physics-equations what positions these two magnets will attract each other in and lock ? In other words - these two sphere...
  34. M

    Medium between poles of magnets

    hello guys, I finally decided to join a forum online and starting asking my " brilliant" :-0 questions..hehehe..oh man i have plenty of those.. OK, am reading the book: understanding physics, by isac asimov. And i am reading about magnetisim now, and its stated two things that bugged my...
  35. E

    Can moving a magnet produce electricity?

    I know that electricity running through a circuit produces a magnetic field...does this work the other way around? Does a permanent magnet in a circuit produce electricity? A colleague of mine is trying to convince me that moving a magnet back and forth in the presence of a circuit can produce...
  36. E

    Attraction and Repulsion Forces Between Magnets

    How do you calculate the attraction and repulsion forces between two magnets? I know it depends on many factors, so for example: two 0.5"x0.5"x0.25" Neodynium magnets with a grade of 42 (Br = 13200 Gauss) that are 0.25" apart from each other (only air is separating them). Thanks for any help...
  37. T

    Permanent magnets & maximum force

    What's the theoretical maximum force? At a certain distance & per kg, i guess. How would you go about calculating this?
  38. W

    Temperature Effects on Permanent Magnets: Exploring Neodymium Magnet Performance

    I am interested in the effects of temperature on Permanent Magnets. I understand that Neodymium magnets lose -0.09 ~ -0.13% of Br/°C and can work stably under 80°C for low Hci Neodymium magnets. However, what happens to them just over this 80°C limit? Do they still have some magnetic strength...
  39. W

    Electromagnets and Permenant Magnets Combined

    Hi, Would an electromagnts or solenoid behave any different if a permenant magnet was attached to it when it is powered up? For example, if I had a opposing pole type electromagnet and I attached the north pole end of a permenant magnet to the north pole end of the unpowered electromagnet. Now...
  40. J

    Permanent Magnets: How Energy Is Stored in Magnetic Fields

    So we can think permanent magnets to be composed of large number of tiny magnetic dipoles? You can hear this in very elementary introductions. I would guess this is some kind of approximation to the spins of the atoms, or something... There is energy stored in the magnetic field, so if these...
  41. J

    What Does North Indicate in Magnets?

    hey ; with magnets we use North and South but for example : what does north stands for ; indicate ? i mean, if u have for example a magnetised material lets say u got it magnetised by rubbing it with an other if the material has more positive charges than negative : do we say its a Norh...
  42. A

    How do you build a home-made speaker using magnets, plastic, coils, etc.?

    Our teacher wants us to construct a speaker that can provide sound (that can be heard from anywhere within the classroom) when connected to wires that are hooked up to some sort of device. I'm unsure of where to start and where to get the supplies. Since we are on the magnetism course, I know...
  43. A

    On superconductors and magnets

    source:British physics olymp. 1995:cool: a small slab of material is placed on a dish containing liquid nitrogen.The material is a superconductor at the temperature of liquid nitrogen.A small but strong magnet is moved near and placed over the slab.The magnet is seen to wobble but remains...
  44. J

    Magnets and electromagnet power?

    Magnets and electromagnet power? It’s said in the <crackpot link removed - Zz> e-books that high voltage 5000v DC electromagnets are more powerful that low voltage 12V DC electromagnets. And in the permanent magnet motor it’s said that “The Attraction of a magnet ( North ) is always stronger...
  45. P

    Why Store Bar Magnets in Pairs with Iron Keepers?

    Homework Statement Why should bar magnets be stored in pairs with soft iron keepers across their ends? Homework Equations none The Attempt at a Solution Is it to prevent damage?
  46. R

    Is there a way to shield a magnets field

    I am wondering if there is a way to put shielding on a simple magnetic bar mad out of neodymium so that the magnetic field is not emanating from all over but just at the ends. I/E a magnet shaped like a can of soda. Putting some type of Shielding on what would be the label section so that the...
  47. L

    A question about permanent magnets

    Does a permanent magnet ever loose it's energy or decrease over time? I read somewhere that a "fixed" magnet's energy will dissipate in time as it does work. I don't know what they mean by fixed. Also, will a permanent magnet work without the Earth's energy (eg. in space).
  48. B

    What are the applications of Quadrupole Neodymium magnets?

    There are lots of patents on Neo magnets and they are difficult to sort out. Some of the patents restrict the use of the magnets that contain cobalt and/or have a tetragonal crystalline structure. Does someone know: What types of magnets contain cobalt? What types of magnets have a...
  49. S

    Permanent Magnets: Find Net Force Acting on Assembly

    Hello! I have a deeply magnetizing question. I have an attractive magnetic assembly and I am interested in finding some forces, acting on its parts. Set-up details ( if to be specific ): I have two cylinder-shaped neo magnets with identical dimensions and properties, such as residual...
  50. V

    Energy from permanent magnets alone

    Hi all, i saw many times while browsing that persons like howard johnson, tom beardson, paul monus, etc., are informing themselves that they have invented motors that run only based on the stored energy of the permanent magnets... are they really having that machines..? if yes, i...
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