A magnet is a material or object that produces a magnetic field. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A low-tech means to detect a magnetic field is to scatter iron filings and observe their pattern, as in the accompanying figure. A "hard" or "permanent" magnet is one that stays magnetized, such as a magnet used to hold notes on a refrigerator door. Permanent magnets occur naturally in some rocks, particularly lodestone, but are now more commonly manufactured. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Lodestone or loadstone refers to either Magnetite, a Magnetic Mineral form of iron(II, Iron(III oxide A "soft" or "impermanent" magnet is one that loses its memory of previous magnetizations. "Soft" magnetic materials are often used in electromagnets to enhance (often hundreds or thousands of times) the magnetic field of a wire that carries an electrical current and is wrapped around the magnet; the field of the "soft" magnet increases with the current. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.

Two measures of a material's magnetic properties are its magnetic moment and its magnetization. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which A material without a permanent magnetic moment can, in the presence of magnetic fields, be attracted (paramagnetic), or repelled (diamagnetic). Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect Liquid oxygen is paramagnetic; graphite is diamagnetic. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the The Mineral graphite, as with Diamond and Fullerene, is one of the Allotropes of carbon. Paramagnets tend to intensify the magnetic field in their vicinity, whereas diamagnets tend to weaken it. "Soft" magnets, which are strongly attracted to magnetic fields, can be thought of as strongly paramagnetic; superconductors, which are strongly repelled by magnetic fields, can be thought of as strongly diamagnetic. Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance

Contents 1 Background on the physics of magnetism and magnets 1.1 Magnetic field 1.2 Magnetic moment 1.3 Magnetization 1.4 Magnetic poles 1.5 Pole naming conventions 2 Descriptions of magnetic behaviors 3 Physics of magnetic behaviors 3.1 Overview 3.2 Physics of paramagnetism 3.3 Physics of diamagnetism 3.4 Physics of ferromagnetism 3.4.1 Magnetic Domains 3.5 Physics of antiferromagnetism 3.6 Physics of ferrimagnetism 3.7 Other types of magnetism 4 Common uses of magnets 5 Magnetization and demagnetization 6 Types of permanent magnets 6.1 Magnetic metallic elements 6.2 Composites 6.2.1 Ceramic or ferrite 6.2.2 Alnico 6.2.3 Ticonal 6.2.4 Injection molded 6.2.5 Flexible 6.3 Rare earth magnets 6.4 Single-molecule magnets (SMMs) and single-chain magnets (SCMs) 6.5 Nano-structured magnets 6.6 Costs 6.7 Temperature 7 Electromagnets 8 Units and calculations in magnetism 8.1 Fields of a magnet 8.2 Calculating the magnetic force 8.2.1 Force between two magnetic poles 8.2.2 Force between two nearby attracting surfaces of area A and equal but opposite magnetizations M 8.2.3 Force between two bar magnets 9 See also 10 Online references 11 Printed references 12 Footnotes and References 13 External links

Background on the physics of magnetism and magnets

Magnetic field

Main article: Magnetic field

The magnetic field (usually denoted B) is a vector field (that is, a vector at every point of space), with a direction and a magnitude that, in SI units is teslas. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Mathematics a vector field is a construction in Vector calculus which associates a vector to every point in a (locally Euclidean space. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic (B can also depend on time. ) Its direction can be obtained from the orientation of a compass needle. A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists Its magnitude (also called strength) is proportional to how strongly the compass needle gets oriented along that direction.

Magnetic moment

Main article: Magnetic moment

A magnet's magnetic moment (also called magnetic dipole moment, and usually denoted μ) is a vector that characterizes the magnet's overall magnetic properties. In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current For a bar magnet, the direction of the magnetic moment points from the magnet's south pole to its north pole, and the magnitude relates to how strong and how far apart these poles are.

A magnet both produces its own magnetic field and it responds to magnetic fields. The strength of the magnetic field it produces is at any given point proportional to the magnitude of its magnetic moment. In addition, when the magnet is put into an "external" magnetic field produced by a different source, it is subject to a torque tending to orient the magnetic moment parallel to the field. A torque (τ in Physics, also called a moment (of force is a pseudo- vector that measures the tendency of a force to rotate an object about The amount of this torque is proportional both to the magnetic moment and the "external" field. A magnet may also be subject to a force driving it in one direction or another, according to the positions and orientations of the magnet and source. If the field is uniform in space the magnet is subject to no net force, although it is subject to a torque.

A wire in the shape of a circle with area A and carrying current I is a magnet, with a magnetic moment of magnitude equal to IA. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere.

Magnetization

Main article: Magnetization

The magnetization of an object is the local value of its magnetic moment per unit volume, usually denoted M, with units A/m. Magnetization is defined as the quantity of Magnetic moment per unit volume The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International It is a vector field, rather than just a vector (like the magnetic moment), because the different sections of a bar magnet generally are magnetized with different directions and strengths (for example, due to domains, see below). A good bar magnet may have a magnetic moment of magnitude 0. 1 A·m² and a volume of 1 cm³, or 0. 000001 m³, and therefore an average magnetization magnitude is 100,000 A/m. Iron can have a magnetization of around a million A/m.

Magnetic poles

Although for many purposes it is convenient to think of a magnet as having distinct north and south magnetic poles, the concept of poles should not be taken literally: it is merely a way of referring to the two different ends of a magnet. The magnet itself may be homogeneous; there are not distinct "north" or "south" particles on opposing sides, and no Magnetic monopole has yet been observed. In Physics, a magnetic monopole is a hypothetical particle that is a Magnet with only one pole (see Maxwell's equations for more on magnetic If a bar magnet is broken in half, in an attempt to separate the north and south poles, the result will be two bar magnets, each of which has both a north and south pole.

The magnetic pole approach is used by most professional magneticians, from those who design magnetic memory to those who design large-scale magnets. If the magnetic pole distribution is known, then outside the magnet the pole model gives the magnetic field exactly. By simply supplementing the pole model field with a term proportional to the magnetization (see Units and Calculations, below) the magnetic field within the magnet is given exactly. This pole model is also called the "Gilbert Model" of a magnetic dipole. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a ^[1]

Another model is the "Ampère Model", where all magnetization is due to the macroscopic effect of microscopic "bound currents", also called "Ampèrian currents". André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers Magnetization is defined as the quantity of Magnetic moment per unit volume For a uniformly magnetized bar magnet in the shape of a cylinder, with poles uniformly distributed on its ends, the net effect of the microscopic bound currents is to make the magnet behave as if there is a macroscopic sheet of current flowing around the cylinder, with local flow direction normal to the cylinder axis. (Since scraping off the outer layer of a magnet will not destroy its magnetic properties, there are subtleties associated with this model as well as with the pole model. What happens is that you have only scraped off a relatively small number of atoms, whose bound currents do not contribute much to the net magnetic moment. ) A right-hand rule due to Ampère tells us how the currents flow, for a given magnetic moment. For the related yet different principle relating to electromagnetic coils see Right hand grip rule. Align the thumb of your right hand along the magnetic moment, and with that hand grasp the cylinder. Your fingers will then point along the direction of current flow. As noted above, the magnetic field given by the Amperian approach and the Gilbert approach are identical outside all magnets, and become identical within all magnets after the Gilbert "field" is supplemented. It is usually difficult to find the Amperian currents on the surface of a magnet, whereas it is often easier to find the effective poles for the same magnet. For one end (pole) of a permanent magnet outside a "soft" magnet, the pole picture of the "soft" magnet has it respond with an image pole of opposite sign to the applied pole; one also can find the Amperian currents on the surface of the "soft" magnet. ^[2]

Pole naming conventions

The north pole of the magnet is the pole which (when the magnet is freely suspended) points towards the magnetic north pole (in northern Canada). The Earth's North Magnetic Pole is the wandering point on the Earth's surface at which the Earth's magnetic field points vertically downwards (i Since opposite poles (north and south) attract whereas like poles (north and north, or south and south) repel, the Earth's present geographic north is thus actually its magnetic south. Confounding the situation further, the Earth's magnetic field occasionally reverses itself. A geomagnetic reversal is a change in the orientation of Earth's magnetic field such that the positions of magnetic north and magnetic south become interchanged

In order to avoid this confusion, the terms positive and negative poles are sometimes used instead of north and south, respectively.

As a practical matter, in order to tell which pole of a magnet is north and which is south, it is not necessary to use the earth's magnetic field at all. For example, one calibration method would be to compare it to an electromagnet, whose poles can be identified via the right-hand rule. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. For the related yet different principle relating to electromagnetic coils see Right hand grip rule.

Descriptions of magnetic behaviors

There are many forms of magnetic behavior, and all materials exhibit at least one of them. Magnets vary both in the permanency of their magnetization, and in the strength and orientation of the magnetic field they create. This section describes, qualitatively, the primary types of magnetic behavior that materials can show. The physics underlying each of these behaviors is described in the next section below, and can also be found in more detail in their respective articles.

• Most popularly found in paper clips, paramagnetism is exhibited in substances which do not produce fields by themselves, but which, when exposed to a magnetic field, reinforce that field by becoming magnetized themselves, and thus get attracted to that field. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field A good example for this behavior can be found in a bucket of nails - if you pick up a single nail, you can expect that other nails will not follow. However, you can apply an intense magnetic field to the bucket, pick up one nail, and find that many will come with it.

• Unscientifically referred to as 'non-magnetic,' diamagnets actually do exhibit some magnetic behavior - just to very small magnitudes. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect In fact, diamagnetic materials, when exposed to a magnetic field, will magnetize (slightly) in the opposite direction, getting (slightly) repelled from the applied field. Superconductors are strongly diamagnetic.

• Ferromagnetic and ferrimagnetic materials are the 'popular' perception of a magnet. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it A ferrimagnetic Interaction is a specific type of Antiferromagnetic interaction in which the net spin of the System is not equal to zero due These materials can retain their own magnetization; a common example is a traditional refrigerator magnet. (The difference between ferro- and ferrimagnetic materials is related to their microscopic structure, as explained below. )

Physics of magnetic behaviors

Overview

Magnetism, at its root, arises from two sources:

• Electric currents, or more generally moving electric charges, create magnetic fields (see Maxwell's Equations). Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric
• Many particles have nonzero "intrinsic" (or "spin") magnetic moments. A subatomic particle is an elementary or composite Particle smaller than an Atom. In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin (Just as each particle, by its nature, has a certain mass and charge, each has a certain magnetic moment, possibly zero. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. )

In magnetic materials, the most important sources of magnetization are, more specifically, the electrons' orbital angular motion around the nucleus, and the electrons' intrinsic magnetic moment (see Electron magnetic dipole moment). The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Atomic physics, the magnetic dipole moment of an Electron is caused by its intrinsic property of spin within a magnetic field The other potential sources of magnetism are much less important: For example, the nuclear magnetic moments of the nuclei in the material are typically thousands of times smaller than the electrons' magnetic moments, so they are negligible in the context of the magnetization of materials. The nuclear magnetic moment is the Magnetic moment of an Atomic nucleus and arises from the spin of the Protons and Neutrons It is mainly a magnetic (Nuclear magnetic moments are important in other contexts, particularly in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). )

Ordinarily, the countless electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) cancel out. This is due, to some extent, to electrons combining into pairs with opposite intrinsic magnetic moments (as a result of the Pauli exclusion principle; see Electron configuration), or combining into "filled subshells" with zero net orbital motion; in both cases, the electron arrangement is so as to exactly cancel the magnetic moments from each electron. The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925 In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. Moreover, even when the electron configuration is such that there are unpaired electrons and/or non-filled subshells, it is often the case that the various electrons in the solid will contribute magnetic moments that point in different, random directions, so that the material will not be magnetic. In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other

However, sometimes (either spontaneously, or due to an applied external magnetic field) each of the electron magnetic moments will be, on average, lined up. Then the material can produce a net total magnetic field, which can potentially be quite strong.

The magnetic behavior of a material depends on its structure (particularly its electron configuration, for the reasons mentioned above), and also on the temperature (at high temperatures, random thermal motion makes it more difficult for the electrons to maintain alignment). In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other Thermal motion is the random motion of Molecules or other small objects that results from their being in thermal equilibrium at a particular Temperature.

Physics of paramagnetism

Main article: Paramagnetism

In a paramagnet there are unpaired electrons, i. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field e. atomic or molecular orbitals with exactly one electron in them. An atomic orbital is a Mathematical function that describes the wave-like behavior of an electron in an atom In Chemistry, a molecular orbital (or MO) is a region in which an Electron may be found in a Molecule. While paired electrons are required by the Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions (summing to zero), an unpaired electron is free to align its magnetic moment in any direction. The Pauli exclusion principle is a quantum mechanical principle formulated by Wolfgang Pauli in 1925 When an external magnetic field is applied, these magnetic moments will tend to align themselves in the same direction as the applied field, thus reinforcing it.

Physics of diamagnetism

Main article: Diamagnetism

In a diamagnet, there are no unpaired electrons, so the intrinsic electron magnetic moments cannot produce any bulk effect. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect In these cases, the magnetization arises from the electrons' orbital motions, which can be understood classically as follows:

When a material is put in a magnetic field, the electrons circling the nucleus will experience, in addition to their Coulomb attraction to the nucleus, a Lorentz force from the magnetic field. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form In Physics, the Lorentz force is the Force on a Point charge due to Electromagnetic fields It is given by the following equation Depending on which direction the electron is orbiting, this force may increase the centripetal force on the electrons, pulling them in towards the nucleus, or it may decrease the force, pulling them away from the nucleus. The centripetal force is the external force required to make a body follow a curved path This effect systematically increases the orbital magnetic moments that were aligned opposite the field, and decreases the ones aligned parallel to the field (in accordance with Lenz's law). Lenz's law (ˈlɛntsɨz ˌlɔː gives the direction of the induced Electromotive force (emf and current resulting from Electromagnetic induction. This results in a small bulk magnetic moment, with an opposite direction to the applied field.

Note that this description is meant only as a heuristic; a proper understanding requires a quantum-mechanical description. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons

Note that all materials, including paramagnets, undergo this orbital response. However, in a paramagnet, this response is overwhelmed by the much stronger opposing response described above (i. e. , alignment of the electrons' intrinsic magnetic moments).

Physics of ferromagnetism

Main article: Ferromagnetism

A ferromagnet, like a paramagnet, has unpaired electrons. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it However, in addition to the electrons' intrinsic magnetic moments wanting to be parallel to an applied field, there is also in these materials a tendency for these magnetic moments to want to be parallel to each other. Thus, even when the applied field is removed, the electrons in the material can keep each other continually pointed in the same direction.

Every ferromagnet has its own individual temperature, called the Curie temperature, or Curie point, above which it loses its ferromagnetic properties. The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906 This is because the thermal tendency to disorder overwhelms the energy-lowering due to ferromagnetic order.

Magnetic Domains

Main article: Magnetic domains

The magnetic moment of atoms in a ferromagnetic material cause them to behave something like tiny permanent magnets. A magnetic domain describes a region within a material which has uniform Magnetization. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it They stick together and align themselves into small regions of more or less uniform alignment called magnetic domains or Weiss domains. A magnetic domain describes a region within a material which has uniform Magnetization. Weiss domains are small areas in a Crystal structure of a ferromagnetic material with uniformly oriented magnetic momenta Magnetic domains can be observed with Magnetic force microscope to reveal magnetic domain boundaries that resemble white lines in the sketch. An Atomic force microscopy (AFM Unlike typical AFM magnetic materials are used for the sample and tip so that not only the atomic force but also the magnetic interaction are detected There are many scientific experiments that can physically show magnetic fields.

When a domain contains too many molecules, it becomes unstable and divides into two domains aligned in opposite directions so that they stick together more stably as shown at the right.

When exposed to a magnetic field, the domain boundaries move so that the domains aligned with the magnetic field grow and dominate the structure as shown at the left. When the magnetizing field is removed, the domains may not return to a unmagnetized state. This results in the ferromagnetic material being magnetized, forming a permanent magnet.

When magnetized strongly enough that the prevailing domain overruns all others to result in only one single domain, the material is magnetically saturated. When a magnetized ferromagnetic material is heated to the Curie point temperature, the molecules are agitated to the point that the magnetic domains lose the organization and the magnetic properties they cause cease. The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906 When the material is cooled, this domain alignment structure spontaneously returns, in a manner roughly analogous to how a liquid can freeze into a crystalline solid. For freezing as a method of food preservation see Frozen food.

Physics of antiferromagnetism

Main article: Antiferromagnetism

In an antiferromagnet, unlike a ferromagnet, there is a tendency for the intrinsic magnetic moments of neighboring valence electrons to point in opposite directions. In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules usuallyrelated to the spins of Electrons align in a regular pattern with neighboring When all atoms are arranged in a substance so that each neighbor is 'anti-aligned', the substance is antiferromagnetic. Antiferromagnets have a zero net magnetic moment, meaning no field is produced by them. Antiferromagnets are less common compared to the other types of behaviors, and are mostly observed at low temperatures. In varying temperatures, antiferromagnets can be seen to exhibit diamagnetic and ferrimagnetic properties.

In some materials, neighboring electrons want to point in opposite directions, but there is no geometrical arrangement in which each pair of neighbors is anti-aligned. This is called a spin glass, and is an example of geometrical frustration. A spin glass is a disordered material exhibiting high magnetic frustration. Geometrical frustration is a phenomenon in Condensed matter physics in which the geometrical properties of the atomic lattice forbid the existence of a unique

Physics of ferrimagnetism

Main article: Ferrimagnetism

Like ferromagnetism, ferrimagnets retain their magnetization in the absence of a field. In Physics, a ferrimagnetic material is one in which the Magnetic moment of the atoms on different sublattices are opposed as in Antiferromagnetism; however However, like antiferromagnets, neighboring pairs of electron spins like to point in opposite directions. These two properties are not contradictory, due to the fact that in the optimal geometrical arrangement, there is more magnetic moment from the sublattice of electrons which point in one direction, than from the sublattice which points in the opposite direction.

The first discovered magnetic substance, magnetite, was originally believed to be a ferromagnet; Louis Néel disproved this, however, with the discovery of ferrimagnetism. Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical Louis Eugène Félix Néel ( November 22, 1904 &ndash November 17, 2000) was a French Physicist born in Lyon

Other types of magnetism

There are various other types of magnetism, such as and spin glass (mentioned above), superparamagnetism, superdiamagnetism, and metamagnetism. A spin glass is a disordered material exhibiting high magnetic frustration. Superparamagnetism is a form of Magnetism. A superparamagnetic material is composed of small Ferromagnetic clusters (e Superdiamagnetism (or perfect diamagnetism) is a Phenomenon occurring in certain materials at Low temperatures characterised by the complete absence of Metamagnetism is a blanket term used loosely in physics to describe a sudden (often dramatic increase in the Magnetization of a material with a small change in an externally

Common uses of magnets

• Magnetic recording media: Common VHS tapes contain a reel of magnetic tape. Magnetic tape is a medium for Magnetic recording generally consisting of a thin magnetizable coating on a long and narrow strip of Plastic. The information that makes up the video and sound is encoded on the magnetic coating on the tape. Common audio cassettes also rely on magnetic tape. The Compact Cassette, often referred to as audio cassette, cassette tape, cassette, or simply tape, is a Magnetic tape sound Similarly, in computers, floppy disks and hard disks record data on a thin magnetic coating. A floppy disk is an increasingly Obsolete data storage medium that is composed of a disk of thin flexible ("floppy" Magnetic storage medium encased A hard disk drive ( HDD) commonly referred to as a hard drive, hard disk, or fixed disk drive, is a Non-volatile storage device

• Credit, debit, and ATM cards: All of these cards have a magnetic strip on one of their sides. A credit card is part of a system of Payments named after the small Plastic card issued to users of the system A debit card (also known as a bank card) is a plastic card which provides an alternative payment method to Cash when making purchases This strip contains the necessary information to contact an individual's financial institution and connect with their account(s).

• Common televisions and computer monitors: TV and computer screens using vacuum tube technology employ an electromagnet to guide electrons to the screen, in order to produce an image -- see the article on cathode ray tubes. Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic A visual display unit, often called simply a monitor or display, is a piece of Electrical equipment which displays images generated from the Video The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or Plasma screens and LCDs use different technologies. A plasma display panel (PDP is a type of Flat panel display now commonly used for large TV displays (typically above 37-inch or 940 mm

• Speakers and Microphones: Most speakers employ a permanent magnet and a current-carrying coil to convert electric energy (the signal) into mechanical energy (movement which creates the sound). For the Marty Friedman album see Loudspeaker (album A loudspeaker, speaker, or speaker system is an electroacoustical The coil is wrapped around a bobbin attached to the speaker cone, and carries the signal as changing current which interacts with the field of the permanent magnet. A coil is a series of loops A coiled coil is a structure where the coil itself is in turn also looping A bobbin is a spindle or cylinder with or without flanges on which Wire, Yarn, thread or film is wound In a Loudspeaker, a diaphragm (also known as the cone) is the thin semi-rigid membrane attached to the central Magnet. The voice coil feels a magnetic force and in response moves the cone and pressurizes the neighboring air, thus generating sound. A voice coil (consisting of a Bobbin, Collar and Winding) is the Coil of Wire attached to the apex of the cone of a Loudspeaker Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Dynamic microphones employ the same concept, but in reverse. A microphone has a diaphragm or membrane attached to a coil of wire. The coil rests inside a specially shaped magnet. When sound vibrates the membrane, the coil is vibrated as well. As the coil moves through the magnetic field, a voltage is generated across the coil (see Lenz's Law). Lenz's law (ˈlɛntsɨz ˌlɔː gives the direction of the induced Electromotive force (emf and current resulting from Electromagnetic induction. This voltage drives current in the wire that is characteristic of the original sound.

• Electric motors and generators: Some electric motors (much like loudspeakers) rely upon a combination of an electromagnet and a permanent magnet, and much like loudspeakers, they convert electric energy into mechanical energy. An electric motor uses Electrical energy to produce Mechanical energy. In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic A generator is the reverse: it converts mechanical energy into electric energy.

• Transformers: Transformers are devices that transfer electric energy between two windings that are electrically isolated but are linked magnetically. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors

• Chucks: Chucks are used in the metalworking field to hold objects. A chuck is a specialised type of clamp used to hold rotating tools or materials Metalworking is craft and practice of working with Metals to create individual parts assemblies or large scale structures If these objects can be held securely with a magnet then a permanent or electromagnetic chuck may be used. A chuck is a specialised type of clamp used to hold rotating tools or materials Magnets are also used in other types of fastening devices, such as the magnetic base, the magnetic clamp and the refrigerator magnet. A magnetic base is a magnetic Fixture based on a magnet that can effectively be turned "on" and "off" at will they are often used in Optics A refrigerator magnet is an ornament attached to a Magnet that is used to post items such as shopping lists or report cards on a Refrigerator, or simply

• A compass (or mariner's compass) is a navigational instrument for finding directions on the Earth. It consists of a magnetized pointer free to align itself accurately with Earth's magnetic field, which is of great assistance in navigation. The cardinal points are north, south, east and west. A compass can be used in conjunction with a marine chronometer and a sextant to provide a very accurate navigation capability. This device greatly improved maritime trade by making travel safer and more efficient. An early form of the compass was invented in China in the 11th century. The familiar mariner's compass was invented in Europe around 1300, as was later the liquid compass and the gyrocompass which does not work with a magnetic field.

• Magic: Naturally magnetic Lodestones as well as iron magnets are used in conjunction with fine iron grains (called "magnetic sand") in the practice of the African-American folk magic known as hoodoo. Lodestone or loadstone refers to either Magnetite, a Magnetic Mineral form of iron(II, Iron(III oxide African Americans or Black Americans are citizens or residents of the United States who have origins in any of the black populations of Africa The stones are symbolically linked to people's names and ritually sprinkled with magnetic sand to reveal the magnetic field. One stone may be utilized to bring desired things to a person; a pair of stones may be manipulated to bring two people closer together in love.

• Art: 1 mm or thicker vinyl magnet sheets may be attached to paintings, photographs, and other ornamental articles, allowing them to be stuck to refrigerators and other metal surfaces. Art refers to a diverse range of Human activities creations and expressions that are appealing to the Senses or Emotions of a human individual The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to

• Science Projects: Many topic questions are often based on magnets. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding For example; how is the strength of a magnet affected by glass, plastic, and cardboard?

• Toys: Due to their ability to counteract the force of gravity at very close range, magnets are often employed in children's toys such as the Magnet Space Wheel to amusing effect. This article is about playthings For other uses of the term see Toy (disambiguation. The Magnet Space Wheel is a Toy that propels a plastic wheel along both sides of a metal track with Magnets built into the wheel

• Magnets can be used to make jewelry. Necklaces and bracelets can have a magnetic clasp. Necklaces and bracelets can be made from small but strong, cylindrical magnets and slightly larger iron or steel balls connected in a pattern that is repeated until it is long enough to fit on the wrist or neck. These accessories may be fragile enough to accidentally come apart, but they also can be disassembled and reassembled with a different design. When connected as a necklace or a bracelet, magnets lose their attraction to other pieces of iron steel because they are already attached to their own iron and steel balls.
• Magnets can pick up magnetic items (iron nails, staples, tacks, paper clips) that are either too small, too hard to reach, or too thin for fingers to hold.

• Magnetic levitation transport, or maglev, is a form of transportation that suspends, guides and propels vehicles (especially trains) via electromagnetic force. This method can be faster than wheeled mass transit systems, potentially reaching velocities comparable to turboprop and jet aircraft (900 km/h, 559 mph). The maximum recorded speed of a maglev train is 581 km/h (361 mph), achieved in Japan in 2003.

• A recently developed use of magnetism is to connect portable computer power cables. Such a connection will occasionally break by accidentally pushing against the cable, but the computer battery prevents interruption of service, and the easy disconnection protects the cable from serious jerks or from being stepped on.

Magnetization and demagnetization

Ferromagnetic materials can be magnetized in the following ways:

• Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it Vibration has been shown to increase the effect. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states Ferrous materials aligned with the earth's magnetic field and which are subject to vibration (e. g. frame of a conveyor) have been shown to acquire significant residual magnetism. A magnetic field much stronger than the earth's can be generated inside a solenoid by passing direct current through it. A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which Direct current ( DC) is the unidirectional flow of Electric charge.
• Stroking - An existing magnet is moved from one end of the item to the other repeatedly in the same direction.
• Placing a steel bar in a magnetic field, then heating it to a high temperature and then finally hammering it as it cools. This can be done by laying the magnet in a North-South direction in the Earth's magnetic field. In this case, the magnet is not very strong but the effect is permanent.

Permanent magnets can be demagnetized in the following ways:

• Heating a magnet past its Curie point will destroy the long range ordering. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906
• Contact through stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets.
• Hammering or jarring will destroy the long range ordering within the magnet.
• A magnet being placed in a solenoid which has an alternating current being passed through it will have its long range ordering disrupted, in much the same way that direct current can cause ordering. A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant

In an electromagnet which uses a soft iron core, ceasing the flow of current will eliminate the magnetic field. The magnetic core is a key component in electrical and electromechanical devices such as Electromagnets Transformers and Inductors A magnetic core is a However, a slight field may remain in the core material as a result of hysteresis. A system with hysteresis can be summarised as a system that may be in any number of states independent of the inputs to the system

Types of permanent magnets

Magnetic metallic elements

Many materials have unpaired electron spins, and the majority of these materials are paramagnetic. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field When the spins interact with each other in such a way that the spins align spontaneously, the materials are called ferromagnetic (what is often loosely termed as "magnetic"). Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it Due to the way their regular crystalline atomic structure causes their spins to interact, some metals are (ferro)magnetic when found in their natural states, as ores. In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across An ore is a volume of rock containing components or Minerals in a mode of occurrence that renders it valuable for mining These include iron ore (magnetite or lodestone), cobalt and nickel, as well the rare earth metals gadolinium and dysprosium (when at a very low temperature). Iron ores are rocks and Minerals from which Metallic Iron can be economically extracted Magnetite is not to be confused with Magnesite or Maghemite. Magnetite is a ferrimagnetic Mineral with chemical Lodestone or loadstone refers to either Magnetite, a Magnetic Mineral form of iron(II, Iron(III oxide Cobalt (ˈkoʊbɒlt is a hard lustrous silver-grey Metal, a Chemical element with symbol Co. Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 Gadolinium (ˌgædəˈlɪniəm is a Chemical element that has the symbol Gd and Atomic number 64 Such naturally occurring (ferro)magnets were used in the first experiments with magnetism. Technology has since expanded the availability of magnetic materials to include various manmade products, all based, however, on naturally magnetic elements.

Composites

Ceramic or ferrite

Ceramic, or ferrite, magnets are made of a sintered composite of powdered iron oxide and barium/strontium carbonate ceramic. Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has The word ceramic is derived from the Greek word κεραμικός ( keramikos) Due to the low cost of the materials and manufacturing methods, inexpensive magnets (or nonmagnetized ferromagnetic cores, for use in electronic component such as radio antennas, for example) of various shapes can be easily mass produced. An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into The resulting magnets are noncorroding, but brittle and must be treated like other ceramics.

Alnico

Alnico magnets are made by casting or sintering a combination of aluminium, nickel and cobalt with iron and small amounts of other elements added to enhance the properties of the magnet. Alnico is an acronym referring to alloys which are composed primarily of Aluminium (symbol Al) Nickel (symbol Ni) and Cobalt (symbol Casting is a manufacturing process by which a liquid material is (usually poured into a mold which Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere WikipediaNaming Sintering offers superior mechanical characteristics, whereas casting delivers higher magnetic fields and allows for the design of intricate shapes. Alnico magnets resist corrosion and have physical properties more forgiving than ferrite, but not quite as desirable as a metal.

Ticonal

Ticonal magnets are an alloy of titanium, cobalt, nickel, and aluminum, with iron and small amounts of other elements. It was developed by Philips for loudspeakers. Koninklijke Philips Electronics NV ( Royal Philips Electronics Inc.

Injection molded

Injection molded magnets are a composite of various types of resin and magnetic powders, allowing parts of complex shapes to be manufactured by injection molding. Injection molding (British moulding In Chemistry, a mixture is a substance made by combining two or more different materials without a chemical reaction occurring (the objects do not bond together Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. The physical and magnetic properties of the product depend on the raw materials, but are generally lower in magnetic strength and resemble plastics in their physical properties. Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products

Flexible

Flexible magnets are similar to injection molded magnets, using a flexible resin or binder such as vinyl, and produced in flat strips or sheets. A vinyl compound is any Organic compound that contains a vinyl group (also called ethenyl) &minus C[[Hydrogen H]] =CH sub>2 These magnets are lower in magnetic strength but can be very flexible, depending on the binder used.

Rare earth magnets

Main article: Rare-earth magnet

'Rare earth' (lanthanoid) elements have a partially occupied f electron shell (which can accommodate up to 14 electrons. Rare-earth magnets are strong permanent magnets made from Alloys of Rare earth elements Rare-earth magnets are substantially stronger than Terminology The Trivial name " Rare earths " is sometimes used to describe all the lanthanoids together with Scandium and Yttrium An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. ) The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore these elements are used in compact high-strength magnets where their higher price is not a concern. The most common types of rare earth magnets are samarium-cobalt and neodymium-iron-boron (NIB) magnets. Samarium-cobalt magnets are primarily composed of Samarium and Cobalt. A neodymium magnet or NIB magnet (a variety of Rare-earth magnet) is a powerful Magnet made of a combination of Neodymium, Iron, and

Single-molecule magnets (SMMs) and single-chain magnets (SCMs)

In the 1990s it was discovered that certain molecules containing paramagnetic metal ions are capable of storing a magnetic moment at very low temperatures. These are very different from conventional magnets that store information at a "domain" level and theoretically could provide a far denser storage medium than conventional magnets. In this direction research on monolayers of SMMs is currently under way. Very briefly, the two main attributes of an SMM are:

1. a large ground state spin value (S), which is provided by ferromagnetic or ferrimagnetic coupling between the paramagnetic metal centres. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it A ferrimagnetic Interaction is a specific type of Antiferromagnetic interaction in which the net spin of the System is not equal to zero due
2. a negative value of the anisotropy of the zero field splitting (D)

Most SMM's contain manganese, but can also be found with vanadium, iron, nickel and cobalt clusters. More recently it has been found that some chain systems can also display a magnetization which persists for long times at relatively higher temperatures. These systems have been called single-chain magnets.

Nano-structured magnets

Some nano-structured materials exhibit energy waves called magnons that coalesce into a common ground state in the manner of a Bose-Einstein condensate. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. A magnon is a Collective excitation of the electrons ' spin structure in a Crystal lattice. A Bose–Einstein condensate (BEC is a State of matter of Bosons confined in an external Potential and cooled to Temperatures very near to ^[3][4]

Costs

The current cheapest permanent magnets, allowing for field strengths, are neodymium-iron-boron (NIB) magnets. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common A neodymium magnet or NIB magnet (a variety of Rare-earth magnet) is a powerful Magnet made of a combination of Neodymium, Iron, and These magnets are more expensive than most other magnetic materials per kg, but due to their intense field are smaller and cheaper in many applications. ^[5]

Temperature

Temperature sensitivity varies, but when a magnet is heated to a temperature known as the Curie point, it looses all of its magnetism, even after cooling below that temperature. The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906 The magnets can often be remagnetised however. Additionally some magnets are brittle and can fracture at high temperatures.

Electromagnets

Main article: electromagnet

An electromagnet in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. A solenoid is a three-dimensional Coil. In Physics, the term solenoid refers to a loop of wire often wrapped around a Metallic core which When electric current flows through the wire, a magnetic field is generated. It is concentrated near (and especially inside) the coil, and its field lines are very similar to those for a magnet. The orientation of this effective magnet is determined via the right hand rule. For the related yet different principle relating to electromagnetic coils see Right hand grip rule. The magnetic moment and the magnetic field of the electromagnet are proportional to the number of loops of wire, to the cross-section of each loop, and to the current passing through the wire.

If the coil of wire is wrapped around a material with no special magnetic properties (e. g. , cardboard), it will tend to generate a very weak field. However, if it is wrapped around a "soft" ferromagnetic material, such as an iron nail, then the net field produced can result in a several hundred- to thousandfold increase of field strength. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it

Uses for electromagnets include particle accelerators, electric motors, junkyard cranes, and magnetic resonance imaging machines. Some applications involve configurations more than a simple magnetic dipole; for example, quadrupole magnets are used to focus particle beams. Quadrupole magnets consist of groups of four Magnets laid out so that in the Multipole expansion of the field the dipole terms cancel and where the lowest significant

Units and calculations in magnetism

How we write the laws of magnetism depends on which set of units we employ. For most engineering applications, MKS or SI (Système International) is common. Two other sets, Gaussian and CGS-emu, are the same for magnetic properties, and are commonly used in physics. The centimetre-gram-second system ( CGS) is a system of physical units.

In all units it is convenient to employ two types of magnetic field, B and H, as well as the magnetization M, defined as the magnetic moment per unit volume.

1. The magnetic induction field B is given in SI units of teslas (T). B is the true magnetic field, whose time-variation produces, by Faraday's Law, circulating electric fields (which the power companies sell). B also produces a deflection force on moving charged particles (as in TV tubes). The tesla is equivalent to the magnetic flux (in webers) per unit area (in meters squared), thus giving B the unit of a flux density. In CGS the unit of B is the gauss (G). One tesla equals 10⁴ G.
2. The magnetic field H is given in SI units of ampere-turns per meter (A-turn/m). The "turns" appears because when H is produced by a current-carrying wire, its value is proportional to the number of turns of that wire. In CGS the unit of H is the oersted (Oe). One A-turn/m equals 4π x 10^-3 Oe.
3. The magnetization M is given in SI units of amperes per meter (A/m). In CGS the unit of M is the emu, or electromagnetic unit. One A/m equals 10^-3 emu. A good permanent magnet can have a magnetization as large as a million amperes per meter. Magnetic fields produced by current-carrying wires would require comparably huge currents per unit length, one reason we employ permanent magnets and electromagnets.
4. In SI units, the relation B = μ₀(H + M) holds, where μ₀ is the permeability of space, which equals 4π x 10^-7 tesla meters per ampere. In CGS it is written as B = H + 4πM. [The pole approach gives μ₀H in SI units. A μ₀M term in SI must then supplement this μ₀H to give the correct field within B the magnet. It will agree with the field B calculated using Amperian currents. ]

Materials that are not permanent magnets usually satisfy the relation M = χH in SI, where χ is the (dimensionless) magnetic susceptibility. Most non-magnetic materials have a relatively small χ (on the order of a millionth), but soft magnets can have χ on the order of hundreds or thousands. For materials satisfying M = χH, we can also write B = μ₀(1 + χ)H = μ₀μ_rH = μH, where μ_r = 1 + χ is the (dimensionless) relative permeability and μ = μ₀μ_r is the magnetic permeability. Both hard and soft magnets have a more complex, history-dependent, behavior described by what are called hysteresis loops, which give either B vs H or M vs H. In CGS M = χH, but χ_SI = 4πχ_CGS, and μ = μ_r.

Caution: In part because there are not enough Roman and Greek symbols, there is no commonly agreed upon symbol for magnetic pole strength and magnetic moment. The symbol m has been used for both pole strength (unit = A·m, where here the upright m is for meter) and for magnetic moment (unit = A·m²). The symbol μ has been used in some texts for magnetic permeability and in other texts for magnetic moment. We will use μ for magnetic permeability and m for magnetic moment. For pole strength we will employ q_m. For a bar magnet of cross-section A with uniform magnetization M along its axis, the pole strength is given by q_m = 'MA, so that M can be thought of as a pole strength per unit area.

Fields of a magnet

Far away from a magnet, the magnetic field created by that magnet is almost always described (to a good approximation) by a dipole field characterized by its total magnetic moment. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a This is true regardless of the shape of the magnet, so long as the magnetic moment is nonzero. One characteristic of a dipole field is that the strength of the field falls off inversely with the cube of the distance from the magnet's center.

Closer to the magnet, the magnetic field becomes more complicated, and more dependent on the detailed shape and magnetization of the magnet. Formally, the field can be expressed as a multipole expansion: A dipole field, plus a quadrupole field, plus an octupole field, etc. A multipole expansion is a mathematical series representing a function that depends on angles — usually the two angles on a sphere. A quadrupole or quadrapole is one of a sequence of configurations of — for example — electric charge or current or gravitational mass that can exist in ideal form but it

At close range, many different fields are possible. For example, for a long, skinny bar magnet with its north pole at one end and south pole at the other, the magnetic field near either end falls off inversely with the square of the distance from that pole.

Calculating the magnetic force

Calculating the attractive or repulsive force between two magnets is, in the general case, an extremely complex operation, as it depends on the shape, magnetization, orientation and separation of the magnets.

Force between two magnetic poles

The force between two magnetic poles is given by:

[1]

where

F is force (SI unit: newton)

q_m1 and q_m2 are the pole strengths (SI unit: ampere-meter)

μ is the permeability of the intervening medium (SI unit: tesla meter per ampere, henry per meter or newton per ampere squared)

r is the separation (SI unit: meter). The newton (symbol N) is the SI derived unit of Force, named after Isaac Newton in recognition of his work on Classical The ampere-metre which has the symbol A m, A-m, or A·m is the SI unit for pole strength in a Magnet. In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second

The pole description is useful to practicing magneticians who design real-world magnets, but real magnets have a pole distribution more complex than a single north and south. Therefore, implementation of the pole idea is not simple. In some cases, one of the more complex formulae given below will be more useful.

Force between two nearby attracting surfaces of area A and equal but opposite magnetizations M

[2]

where

A is the area of each surface, in m²

M is their magnetization, in A/m.

μ₀ is the permeability of space, which equals 4π x 10^-7 tesla-meters per ampere

Force between two bar magnets

The force between two identical cylindrical bar magnets placed end-to-end is given by:

[3]

where

B₀ is the magnetic flux density very close to each pole, in T,

A is the area of each pole, in m²,

L is the length of each magnet, in m,

R is the radius of each magnet, in m, and

x is the separation between the two magnets, in m

'B₀ =M relates the flux density at the pole to the magnetization of the magnet.

See also

Online references

• HyperPhysics E/M, good complete tree diagram of electromagnetic relationships with magnets
• Maxwell's Equations and some history. A B-H Analyzer is an instrument that measures the AC magnetic characteristics of soft Magnetic materials It measures Residual flux density B_R Earnshaw's theorem states that a collection of Point charges cannot be maintained in a stable stationary equilibrium configuration solely by the Electrostatic An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of The electromagnetic field is a physical field produced by electrically charged objects. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a In Physics, a magnetic monopole is a hypothetical particle that is a Magnet with only one pole (see Maxwell's equations for more on magnetic In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. A single-molecule magnet or SMM is an object that is composed of Molecules each of which behaves as an individual superparamagnet. Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Magnet therapy, magnetic therapy, magnetotherapy or magnotherapy is a Complementary and alternative medicine practice involving the use of static A neodymium magnet or NIB magnet (a variety of Rare-earth magnet) is a powerful Magnet made of a combination of Neodymium, Iron, and A Halbach array is a special arrangement of permanent Magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric . .
• Detailed Theory on Designing a Solenoid or a Coil Gun

Printed references

1. "positive pole n. " The Concise Oxford English Dictionary. The Oxford English Dictionary ( OED) published by the Oxford University Press (OUP is a comprehensive Dictionary of the English Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2004. Oxford Reference Online. Oxford University Press.

2. Wayne M. Saslow, "Electricity, Magnetism, and Light", Academic (2002). ISBN 0-12-619455-6. Chapter 9 discusses magnets and their magnetic fields using the concept of magnetic poles, but it also gives evidence that magnetic poles don't really exist in ordinary matter. Chapters 10 and 11, following what appears to be a 19th century approach, use the pole concept to obtain the laws describing the magnetism of electric currents.

3. Edward P. Furlani, "Permanent Magnet and Electromechanical Devices: Materials, Analysis and Applications", Academic Press Series in Electromagnetism (2001). ISBN 0-12-269951-3.

Footnotes and References

External links

• Articles, tutorials and other educational information about magnets National High Magnetic Field Laboratory
• Answers to several questions from curious kids about magnets
• Magnetic units are discussed here
• Kids Konnect - Magnets

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