An electromagnet is a type of magnet 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 like iron and attracts or repels other magnets whose magnetic field Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field is produced by the flow of electric current Electric current means, depending on the context, a flow of electric charge or the rate of flow of electric charge (a quantity). This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both. The magnetic field disappears when the current ceases.

Electromagnets attracts paper clips when current is applied creating a magnetic field. The electromagnet loses them when current and magnetic field are removed.

Contents

Introduction

A wire with an electric current Electric current means, depending on the context, a flow of electric charge or the rate of flow of electric charge (a quantity). This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both passing through it generates a magnetic field Magnetic fields surround magnetic materials and electric currents and are detected by the force they exert on other magnetic materials and moving electric charges. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field around it; this is a simple electromagnet. The strength of magnetic field generated is proportional to the amount of current.

Current (I) through a wire produces a magnetic field (B). The field is oriented according to the right-hand rule The right hand grip rule is a physics principle applied to electric current passing through a solenoid, resulting in a magnetic field. When you wrap your right hand around the solenoid with your fingers in the direction of the conventional current, your thumb points in the direction of the magnetic north pole. It can also be applied to electricity.

In order to concentrate the magnetic field generated by a wire, it is commonly wound into a coil A coil is a series of loops. A coiled coil is a structure where the coil itself is in turn also looping, these objects are used commonly and are very important, some of their functions may be in bikes, cars trains and planes. Often used in conjunction with a thread, where many turns of wire sit side by side. The magnetic field of all the turns of wire passes through the center of the coil, creating a strong magnetic field there. A coil forming the shape of a straight tube (a helix A helix is a type of space curve, i.e. a smooth curve in three-dimensional space. It is characterised by the fact that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for example, a spiral ramp –) is called a solenoid A solenoid[nb 1] is a three-dimensional coil wound into a tightly packed helix. In physics, the term solenoid refers to a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as; a solenoid that is bent into a donut shape so that the ends meet is called a toroid Toroidal inductors and transformers are electronic components, typically consisting of a circular ring-shaped magnetic core of iron powder, ferrite, or other material around which wire is coiled to make an inductor. Toroidal coils are used in a broad range of applications, such as high-frequency coils and transformers. Toroidal inductors can have. Much stronger magnetic fields can be produced if a "core A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical and electromechanical devices such as electromagnets, transformers, electric motors, and inductors. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability," of ferromagnetic Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type; it is the only type that can produce forces strong enough to be felt, and is responsible for the common phenomena of material, such as soft iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used, is placed inside the coil. The ferromagnetic core magnifies the magnetic field to thousands of times the strength of the field of the coil alone, due to the high magnetic permeability In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ. The term was coined in September, 1885 by Oliver Heaviside. The reciprocal of magnetic permeability is magnetic reluctivity μ of the ferromagnetic material. This is called a ferromagnetic-core or iron-core electromagnet.

The direction of the magnetic field through a coil of wire can be found from a form of the right-hand rule The right hand grip rule is a physics principle applied to electric current passing through a solenoid, resulting in a magnetic field. When you wrap your right hand around the solenoid with your fingers in the direction of the conventional current, your thumb points in the direction of the magnetic north pole. It can also be applied to electricity.[1][2][3][4][5][6] If the fingers of the right hand are curled around the coil in the direction of current flow (conventional current Electric current means, depending on the context, a flow of electric charge or the rate of flow of electric charge (a quantity). This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both, flow of positive charge Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields. The interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the) through the windings, the thumb points in the direction of the field inside the coil. The side of the magnet that the field lines emerge from is defined to be the north pole.

The main advantage of an electromagnet over a permanent magnet 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 and attracts or repels other magnets is that the magnetic field can be rapidly manipulated over a wide range by controlling the amount of electric current. However, a continuous supply of electrical energy is required to maintain the field.

Magnetic field produced by a solenoid A solenoid[nb 1] is a three-dimensional coil wound into a tightly packed helix. In physics, the term solenoid refers to a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create controlled magnetic fields and can be used as (coil of wire). The crosses are wires in which current is moving into the page; the dots are wires in which current is moving up out of the page.

How the iron core works

The material of the core A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical and electromechanical devices such as electromagnets, transformers, electric motors, and inductors. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, of the magnet (usually iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used) is composed of small regions called magnetic domains A magnetic domain describes a region within a magnetic material which has uniform magnetization. This means that the individual magnetic moments of the atoms are aligned with one another and point in the same direction. Below a temperature called the Curie temperature, a piece of ferromagnetic material undergoes a phase transition and its that act like tiny magnets (see ferromagnetism Ferromagnetism is the basic mechanism by which certain materials form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism is the strongest type; it is the only type that can produce forces strong enough to be felt, and is responsible for the common phenomena of). Before the current in the electromagnet is turned on, the domains in the iron core point in random directions, so their tiny magnetic fields cancel each other out, and the iron has no large scale magnetic field. When a current is passed through the wire wrapped around the iron, its magnetic field penetrates the iron, and causes the domains to turn, aligning parallel to the magnetic field, so their tiny magnetic fields add to the wire's field, creating a large magnetic field that extends into the space around the magnet. The larger the current passed through the wire coil, the more the domains align, and the stronger the magnetic field is. Finally all the domains are lined up, and further increases in current only cause slight increases in the magnetic field: this phenomenon is called saturation Saturation is most clearly seen in the magnetization curve of a substance, as a bending to the right of the curve (see graph at right). As the H field increases, the B field approaches a maximum value asymptotically, the saturation level for the substance. Technically, above saturation, the B field continues increasing, but at the paramagnetic.

When the current in the coil is turned off, most of the domains lose alignment and return to a random state and the field disappears. However some of the alignment persists, because the domains have difficulty turning their direction of magnetization, leaving the core a weak permanent magnet. This phenomenon is called hysteresis Hysteresis refers to systems that have memory, where the effects of the current input to the system are experienced with a certain delay in time. Such a system may exhibit path dependence, or "rate-independent memory" . Hysteresis phenomena occur in magnetic materials, ferromagnetic materials and ferroelectric materials, as well as in and the remaining magnetic field is called remanent magnetism Remanence is the magnetization left behind in a medium after an external magnetic field is removed. It is denoted in equations as Mr. In engineering applications it is often assumed that the magnetization M is synonymous with the residual flux density B hence the remanence is frequently denoted as BR (see the image). Only substances that can be. The residual magnetization of the core can be removed by degaussing Degaussing is the process of decreasing or eliminating an unwanted magnetic field. It is named after Carl Friedrich Gauss, an early researcher in the field of magnetism. Due to magnetic hysteresis it is generally not possible to reduce a magnetic field completely to zero, so degaussing typically induces a very small "known" field.

Electromagnet used in the Tevatron The Tevatron is a United States circular particle accelerator at the Fermi National Accelerator Laboratory in Batavia, Illinois and is the second highest energy particle collider in the world after the Large Hadron Collider . The Tevatron is a synchrotron that accelerates protons and antiprotons in a 6.28 km (3.90 miles) ring to energies of up to 1 particle accelerator A particle accelerator is a device that uses electric fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field, Fermilab, USA Laboratory electromagnet used in physics experiments, around 1910 Magnet in a mass spectrometer Mass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds. The MS principle consists of ionizing chemical compounds to generate charged molecules or molecule fragments AC electromagnet on the stator The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors of an electric motor An electric motor uses electrical energy to produce mechanical energy, very typically through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Many types of electric motors can be run as generators, and vice versa Magnets in an electric bell

History

Sturgeon's electromagnet, 1823

Danish scientist Hans Christian Ørsted Hans Christian Ørsted was a Danish physicist and chemist who is best known for discovering that electric currents can create magnetic fields which is an important part of Electromagnetism. He shaped post-Kantian philosophy and advances in science throughout the late nineteenth century. He was also the first modern thinker to explicitly describe discovered in 1820 that electric currents create magnetic fields. British scientist William Sturgeon William Sturgeon was an English physicist and inventor who made the first electromagnets, and invented the first English practical electric motor invented the electromagnet in 1824.[7][8] His first electromagnet was a horseshoe-shaped piece of iron that was wrapped with about 18 turns of bare copper wire (insulated An insulator, also called a dielectric, is a material that resists the flow of electric current. An insulating material has atoms with tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators or insulation, intended to support or separate electrical conductors without passing current wire didn't exist yet). The iron was varnished Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss sheens by the addition of "flatting" to insulate it from the windings. When a current was passed through the coil, the iron became magnetized and attracted other pieces of iron; when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces (roughly 200 grams), it could lift nine pounds (roughly 4 kilos) when the current of a single-cell battery was applied. However, Sturgeon's magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns. Beginning in 1827, US scientist Joseph Henry Joseph Henry was an American scientist who served as the first Secretary of the Smithsonian Institution, as well as a founding member of the National Institute for the Promotion of Science, a precursor of the Smithsonian Institution. During his lifetime, he was highly regarded. While building electromagnets, Henry discovered the electromagnetic systematically improved and popularized the electromagnet.[9] By using wire insulated by silk thread he was able to wind multiple layers of wire on cores, creating powerful magnets with thousands of turns of wire, including one that could support 2063 pounds. The first major use for electromagnets was in telegraph sounders When a current flows through the induction coil, the resulting magnetic field attracts an armature that is held up against a metal arm. When the current is switched off, the armature drops to its resting position, resulting in a "click". When the current returns, the armature is raised back to the upper arm resulting in a "clack.&.

The magnetic domain theory of how ferromagnetic cores work was first proposed in 1906 by French physicist Pierre-Ernest Weiss Pierre-Ernest Weiss was a French physicist who developed the domain theory of ferromagnetism in 1907. Weiss domains and the Weiss magneton are named after him, and the detailed modern quantum mechanical theory of ferromagnetism was worked out in the 1920s by Werner Heisenberg Werner Heisenberg was a German theoretical physicist who made foundational contributions to quantum mechanics and is best known for asserting the uncertainty principle of quantum theory. In addition, he made important contributions to nuclear physics, quantum field theory, and particle physics, Lev Landau Lev Davidovich Landau was a prominent Soviet physicist who made fundamental contributions to many areas of theoretical physics. His accomplishments include the co-discovery of the density matrix method in quantum mechanics, the quantum mechanical theory of diamagnetism, the theory of superfluidity, the theory of second order phase transitions, the, Felix Bloch Felix Bloch was a Swiss physicist, working mainly in the U.S and others.

Uses of electromagnets

Electromagnets are very widely used in electric and electromechanical In engineering, electromechanics combines the sciences of electromagnetism of electrical engineering and mechanics. Mechanical engineering in this context refers to the larger discipline which includes chemical engineering, and other related disciplines. Electrical engineering in this context also encompasses software engineering, computer devices, including:

Analysis of ferromagnetic electromagnets

For definitions of the variables below, see box at end of article.

Industrial electromagnet lifting scrap iron, 1914

The magnetic field of electromagnets in the general case is given by Ampere's Law:

which says that the integral of the magnetizing field H around any closed loop of the field is equal to the sum of the current flowing through the loop. Another equation used, that gives the magnetic field due to each small segment of current, is the Biot-Savart law. Computing the magnetic field and force exerted by ferromagnetic materials is difficult for two reasons. First, because the strength of the field varies from point to point in a complicated way, particularly outside the core and in air gaps, where fringing fields and leakage flux must be considered. Second, because the magnetic field B and force are nonlinear functions of the current, depending on the nonlinear relation between B and H for the particular core material used. For precise calculations the finite element method is used.

Magnetic circuit - the constant B field approximation

However, for a typical DC electromagnet in which the magnetic field path is confined to a loop or circuit of core material, possibly broken by a few narrow air gaps, a simplification can be made. A common simplifying assumption satisfied by many electromagnets, which will be used in this section, is that the magnetic field strength B is constant around the magnetic circuit and zero outside it. Most of the magnetic field will be concentrated in the core material. Within the core the magnetic field will be approximately uniform across any cross section, so if in addition the core has roughly constant area throughout its length, the field in the core will be constant. This just leaves the air gaps, if any, between core sections. In the gaps the magnetic field lines are no longer confined by the core, so they 'bulge' out beyond the outlines of the core before curving back to enter the next piece of core material, reducing the field strength in the gap. The bulges are called fringing fields. However, as long as the length of the gap is smaller than the cross section dimensions of the core, the field in the gap will be approximately the same as in the core. In addition, if parts of the core are too near other parts, some of the magnetic field lines will take 'short cuts' and not pass through the entire core circuit. This also occurs in the field near the windings, if the windings are not wrapped tightly around the core. This is called leakage flux. It also results in a lower magnetic field in the core. Therefore the equations in this section are valid for electromagnets for which:

  1. the magnetic circuit is a single loop.
  2. the core has roughly the same cross sectional area throughout its length.
  3. any air gaps between sections of core material are not large compared with the cross sectional dimensions of the core.
  4. there is negligible leakage flux

The main nonlinear feature of ferromagnetic materials is that the B field saturates at a certain value, which is around 1.6 teslas (T) for most high permeability core steels. The B field increases quickly with increasing current up to that value, but above that value the field levels off and increases at the much smaller paramagnetic value, regardless of how much current is sent through the windings. So the strength of the magnetic field possible from an iron core electromagnet is limited to 1.6-2 T.

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