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. O

    How to model a permanent magnet?

    This is sort of a thought experiment. I want to find out if my approach to this is correct. How can I analytically find the magnetic field from a permanent magnet? My approach would be to consider the magnet to be a lattice, with each lattice point being a molecule with a magnetic dipole...
  2. cobalt124

    Potential magnet damage to laptop HDD

    My specific question is can the magnets in an Ashton BA15 40W bass amp damage the HDD in a laptop (we have a Samsung about a year and a quarter old and an Acer about a year old). I've read the following threads: https://www.physicsforums.com/showthread.php?t=411895&highlight=magnet...
  3. H

    Magnet with single pole creation

    Hi, I am proposing a simple way to create a magnet with single pole. Not being a physics/science graduate, this came out of interest of thinking only. Lets consider a sphere, which is hollow inside and has a thickness to it at the surface only. If i cut a certain segment and make it out of...
  4. D

    Magnet - right hand rule - direction of compass North

    Homework Statement A length of wire extends upward through a piece of cardboard, bends around, forming a loop, and extends back down through the cardboard. All that is visible above the surface of the cardboard is this loop of wire. From your perspective, you are looking downward on the piece...
  5. A

    Say you have a magnet, one end of the magnet has a positive charge and

    Say you have a magnet, one end of the magnet has a positive charge and the other end has a negative charge. What would happen to the magnet if you broke it in half?
  6. S

    How Does a Magnet Affect Compass Direction in a Dual Coil Setup?

    The north pole of a permanent magnet was held over a coil of wire with a hollow core, as shown. A second coil with a hollow core was connected to the first coil as shown. A magnetic compass needle was placed into the second coil, free to rotate in a vertical circle as shown. If the north pole of...
  7. J

    Where Does the Energy Come From When a Magnet Moves Over a Paperclip?

    My apologies for posting something that I'm sure people will say has been answered before, but a trawl through the results of a search of magnets didn't come up with a satisfactory answer. If I hold a permanent magnet a few centimeters over my desk and slowly move it across a paperclip the...
  8. R

    Closed loop vs open loop resistance magnet drop demo

    Hello everyone, curious about something here. I saw a demonstration lately were a magnet was dropped down a copper pipe and the magnet dropped very much slower than expected. What I got to thinking was, if you replaced the copper pipe with the same quantity of insulated copper wire in a...
  9. P

    Magnet Side Force: Explaining the Physics

    When 2 magnets are on opposite sides of a table by moving one magnet the other moves also. could someone explain the physics/formulas or relations that correspond to this. Thanks
  10. I

    Bar magnet at constant velocity, what is the direction of the induced current?

    Homework Statement A bar magnet is spun at constant angular speed w around an axis as shown in Figure P31.38. A stationary flat rectangular conducting loop surrounds the magnet, and at t = 0, the magnet is oriented as shown. Make a qualitative graph of the induced current in the loop as a...
  11. S

    Force of a solenoid on a magnet?

    I'm trying to calculate the force between a solenoid and a magnet inside that solenoid. Would someone be able to explain how I would be able to calculate the force a solenoid of n number of turns and l length with a current I running through it would put on a magnet whose center is a distance d...
  12. B

    Creating emf with a wire coil and magnet

    Homework Statement We have seen this week that there are 3 ways to generate an emf (voltage or a current) using Faraday's law. Suppose you have a permanent magnet (of your choice), and 5-cm radius coil of wire with 100 loops, and a sledge hammer. Describe the three different ways the loop of...
  13. C

    EMI - Current in solenoid due to magnet

    Homework Statement The Attempt at a Solution Suppose that N pole of magnet is facing the solenoid considering view from magnet when the magnet moves close ... current is anticlockwise and increase from 0 to max till magnet reach starting of solenoid when it enters the solenoid ...
  14. B

    Capacitor and 1 British Pound MAGNET

    Hi guys. I've got an interesting questions. I found it tricky maybe somebody knows the answer. When I attach to DC supply a capacitor with a coin 1 British Pound parallel to the capacitor and connected by two wires coming out of the capacitor, I always get kind of sparkles in my coin, the supply...
  15. P

    Does waving a magnet back and fourth produce an EM wave?

    If you take a permanent magnet and wave it back and fourth, or even just move it along in one direction, this seems like it should create an electromagnetic wave. If so, how would one compute the frequency, and could you possibly detect it with a radio if you shielded it from other noise?
  16. R

    Magnet which loses its magnetic grip when current passes through

    Problem Traditional electromagnets create a magnetic field when current passes through them. What I need is a magnet that loses its magnetic grip when current passes through. Is there a particular name for these kind of magnets / systems? Application I want the magnet to hold a metal...
  17. K

    Can a lift electromagnet pull a permanent magnet?

    A lift electromagnet has N + S pole on the same side. will it push or pull a permanent magnet which has N & S pole on opposite side? If I have a lift electromagnet and a permanent magnet, both can pull 100 lbs. What is the break away force if I put them together? Thanks
  18. B

    Exploring the Potential of Vertically Stacked Permanent Magnet Alternators

    Greetings, I have been working on a permanent magnet alternator, axial flux configuration. It has been configured with vertically staked stators and rotors. The traditional fabrication technique the stator is one large diameter with a large diameter magnet rotor above and the below the stator...
  19. P

    Why doesn't my magnet stick to the hhd magnetic plate?

    I opened my harddisk and put a magnet on the plates but the plate acts like a piece of wood. I would expect the magnet to stick to the plate. It is a magnetic plate afterall! My "magnet" is in fact a row of neo cube balls which are quite strong magnets and small. So I would surely feel or see a...
  20. L

    How to make a large stern gerlach magnet

    Hello Forum, Does anyone know of any references on the construction of a Stern-Gerlach magnet? Most of the references I have seen so far discuss magnets that provide a constant field gradient (in the z-axis) over a few millimetres. Since I have a circular beam of about 1 cm diameter, I need a...
  21. Fredrik

    The effect of the magnet in a Stern-Gerlach experiment

    A beam of silver atoms (which are electrically neutral spin-1/2 particles) enters an inhomogeneous magnetic field, and is split in two. The state of an atom that has passed the magnet is often described as |U>|↓>+|L>|↑>, where |U> and |L> are states that are localized to the upper and...
  22. C

    Levitating a magnet over a superconducting ring?

    Is it possible to levitate a magnet in a superconducting pipe or a ring? Is it possible to try to calculate this using the method of images and treat the magnet as a little current loop? Any input will be much appreciated.
  23. M

    Force from a magnet passing through coils

    Hi there I'm engineering a suspension system with the damper consisting of a magnet going through some coils. As the energy produced from this is proportional to the velocity of the magnet, this would be ideal for an "energetic" damper. To calculate the damping coefficient produced, I...
  24. N

    Calculating Flux from a Permanent Magnet

    I am hoping someone here has experience with permanent magnets. I have a theory on how to size a permanent magnet for an alternator I am designing, and I want someone to confirm that my technique will yield a result that is useful enough to go through the expense of building a prototype. My...
  25. L

    Levitating Magnet with Load of 12oz: Shielding Electronics & Transmitter

    So basically i have this powerful electromagnet that generates an electromagnetic field that can levitate another magnet and withhold a load of 12oz and still levitate: My problem is, I want to be able to use electronics and send wireless signals through this strong magnetic field. I can...
  26. N

    Finding airgap flux from a permanent magnet

    The problem I am having is that I cannot seem to find the magneto-motive force of a permanent magnet. Most material tables give a Hc in kA/m, which I take to mean I multiply by the length of the magnet, then by the area of the magnet to get my total magneto-motive force. So does...
  27. U

    How to make a bar magnet from wire

    a barmagnet seems to be a densly winded solenoid just with the exception that the field of the solenoid is allmost zero outside and also at its ends but strong in the inside witch doesn't agree with barmagnets
  28. J

    Explaining How Magnet Dropping Down a Copper Tube Conserves Energy

    Help me explain how the "magnet dropped down a copper tube" demo conserves energy I've tried explaining to this person that the potential energy you give a magnet when you do work against gravity to raise it up to the copper tube is all the energy it has to deal with, and once dropped down it...
  29. S

    Calculating the force between a magnet and an electromagnet

    Hello. I would just like to begin by saying that I am very aware of the vast complexity of the subject of magnetism. Still, I have been hoping to find a way to get a basic idea of how much a magnet and an electromagnet are attracted or repelled by one another. I do not need highly perfect and...
  30. B

    Double permanent magnet generator

    So I can't seem to find out why generators aren't designed so that the coils are passing in between TWO magnets N facing in and S facing out, and then S facing in N facing out etc. The flux density between two magnets is obviously greater and the flux lines are 'straighter' (more lines of flux...
  31. P

    Passing current through a magnet

    I think magnet has to be a conductor of electricity if is made of iron or steel. So, What happens when we pass a direct current through a magnet? What if we pass through AC? Does the passage of current effect the strength of the magnet?
  32. S

    Weak & Strong Magnet attract each other no matter what polarity

    Recently while working with electromagnet , we noticed one thing. I we bring strong magnet near very weak PM or electromagnet, It will attract the weak one whatever is the polarity of magnets. we increased power to electromagnet then it was giving repulsion. I did't understand this...
  33. J

    When you make a magnet is PE created?

    When you "make" a magnet is PE created? Okay my understanding of a magnet is that if a magnetic material is placed in it's field then the Magnetic Potential Energy is converted to Kinetic Energy in the object and thus you get the attractive force and movement in the object which subsequently...
  34. G

    What is the difference between permanent magnet fields and electromagnet fields?

    What is the difference between permanent magnet fields and electromagnet fields?
  35. T

    Has anyone ever considered this issue with magnet falling in copper tube?

    Has anyone ever considered this issue with magnet falling in copper tube?? Homework Statement I must explain why a magnet falling in a copper tube slows down. Homework Equations F = B^qv However, I must *explain* this, I don't have to calculate anything The Attempt at a Solution...
  36. B

    Permanent magnet on the surface of a hollow sphere

    Hello I would like to calculate the magnetic flux density given by a permanent magnet which is placed about the surface of a iron hollow sphere (assume mur = Inf). Actually, I am interested in the flux density just outside the hollow sphere. The idea is to replace the magnet with equivalent...
  37. S

    Calculating Current & Voltage in Coil with Magnet

    I have been wondering how to calculate how much current and voltage would be induced through a 2m length of coil when a magnet passes through. The coil being 30mm in diameter with 1mm thick wire coiled around 200 times (for ease of calculation so cable would roughly be 18.8m long) with a...
  38. J

    Peak Voltage vs magnet position in an A.C generator

    I have a question about a magnets position over a coil of wire in an A.C generator. Is the voltage in the coil at Peak as long as its covered by the magnet? and then the voltage starts to decrease to 0 volts as the magnet starts uncovering the coil until the magnet totally uncovers the coil and...
  39. J

    Magneto, determine magnet strength and voltage at rpm

    Homework Statement A small engine flywheel rotates at 2000rpm and has 4 permanent magnents pressed into the flywheel at a radius of 10cm spaced 90deg apart 1.2cm diameter magnets. A 1.2cm diameter pickup coil with 500 turns is at the edge of the flywheel. Max voltage detected is .76 volts...
  40. P

    Force from Infinitely Long Cylindrical Magnet on Magnetic Dipole

    Homework Statement What is the force from an infinitely long cylindrical magnet on a magnetic dipole? Homework Equations M=Mz (given in problem) The Attempt at a Solution My argument for this solution that since the magnetization is in the z direction and the cylinder is...
  41. W

    Will a Magnet-Powered Torch "Run Out"?

    i'm sure we have all seen the little torches with a magnet inside that you shake to generate the required electricity to power the bulb... we were talking about them in the pub the other night and the following question came up... my question is this, will the magnet ever "run out", and by...
  42. N

    What happens when you spin a powerful magnet at high speeds?

    Lets say we have a spherical shaped and very powerful magnet. Let's say it has a 3" diameter and has some good weight to it. What would happen if you spun the magnet at great speeds. Let's say for the sake of argument say some 300,000 RPM. Could the centrifugal for created by the spinning...
  43. S

    Strong magnet and was standing in metal shoes

    If I had a strong magnet and was standing in metal shoes that were welded to a metal trashcan lid, could I levitate myself with said magnet?
  44. R

    How Does Magnet Pull Force Influence Weight Lifting and Coil Rotation?

    Let's say a magnet is attached to an object that weigh's 15 pound's . Then someone attempt's to take the magnet off the object . The object then go's up with the magnet (still being attached to it ) Does that mean the magnet can lift 15 pound's ? Also when a magnet is rotateing through a coil...
  45. E

    Building a NEO Magnet Magnetizer

    I am looking to build a NEO magnet magnetizer for RC motors. Currently we are having issues with the motors losing magnet strength after they are run. The rotors to replace are $30+. In the Old days, we ran brushed ceramic magnet motors. With these, we had a magnetizer to simply zap the motors...
  46. T

    Magnetic field: Bar magnet & coil. Number of Turns?

    Hey all, I'm new to this site, so bear with me here! First post woot! Homework Statement A bar magnet with magnetic dipole moment 0.5 A m2 lies on the negative x-axis, as shown in the diagram. A compass is located at the origin. Magnetic North is in the negative z direction. Between the bar...
  47. Z

    Magnet, wire and Newtons third law

    I have been thinking about a bar magnet and an infinite wire in free space. The wire is positioned below the north pole of magnet and carries a current. 1) The force from the magent on the wire: Due to the magnetic field, the Lorentz force on the electrons in the wire creates a force on the...
  48. C

    Negative pole of magnet deflects electrons?

    I watched a video there about cathode ray tubes and the guy in the video demonstrated the negative pole of a magnet deflecting the beam and the positive pole attracting the beam. I know that moving electrical charges create magnetic fields but I didn't know their magnetic fields always deflect...
  49. B

    Tracking Wire Position with Electromagnet & Permanent Magnet

    I am trying to come up with a design that would track the position of a wire. The wire will have a permanent magnet attached to its tip. I will use a electromagnet to move the wire in only 1 dimension. Here is what I was thinking... I would put a stationary aluminum plate some distance from...
  50. M

    Creating a Poleless Magnet Ring

    Has anyone heard of a permanent magnet in the shape of a ring or toroid with no poles? I believe that one could be made by winding a ring of magnetic material, such as steel, with a wire winding, like one winding of a toroidal transformer. DC current could then be passed through the winding...
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