Magnets and Magnetism Directed Reading a Answers

Class of physical phenomena

Magnetism is the grade of concrete attributes that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is i aspect of the combined phenomenon of electromagnetism. The virtually familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. The rare-earth metals neodymium and samarium are less common examples. The prefix ferro- refers to iron, considering permanent magnetism was first observed in lodestone, a class of natural atomic number 26 ore called magnetite, Iron₃O₄.

All substances exhibit some type of magnetism. Magnetic materials are classified according to their bulk susceptibility.^[1] Ferromagnetism is responsible for near of the effects of magnetism encountered in everyday life, just there are actually several types of magnetism. Paramagnetic substances, such as aluminum and oxygen, are weakly attracted to an practical magnetic field; diamagnetic substances, such as copper and carbon, are weakly repelled; while antiferromagnetic materials, such every bit chromium and spin glasses, accept a more complex relationship with a magnetic field. The force of a magnet on paramagnetic, diamagnetic, and antiferromagnetic materials is usually as well weak to exist felt and can be detected just past laboratory instruments, so in everyday life, these substances are often described equally non-magnetic.

The magnetic state (or magnetic phase) of a material depends on temperature, pressure, and the applied magnetic field. A textile may showroom more than 1 form of magnetism every bit these variables change.

The strength of a magnetic field most always decreases with distance, though the exact mathematical relationship betwixt strength and distance varies. Dissimilar configurations of magnetic moments and electric currents can outcome in complicated magnetic fields.

Just magnetic dipoles take been observed, although some theories predict the beingness of magnetic monopoles.

History [edit]

Lodestone, a natural magnet, attracting iron nails. Ancient humans discovered the property of magnetism from lodestone.

An illustration from Gilbert's 1600 De Magnete showing one of the primeval methods of making a magnet. A blacksmith holds a piece of carmine-hot iron in a northward–south direction and hammers it as it cools. The magnetic field of the Earth aligns the domains, leaving the iron a weak magnet.

Drawing of a medical treatment using magnetic brushes. Charles Jacque 1843, French republic.

Magnetism was first discovered in the ancient globe, when people noticed that lodestones, naturally magnetized pieces of the mineral magnetite, could attract atomic number 26.^[2] The discussion magnet comes from the Greek term μαγνῆτις λίθος magnētis lithos,^[3] "the Magnesian stone,^[4] lodestone." In aboriginal Greece, Aristotle attributed the beginning of what could be called a scientific discussion of magnetism to the philosopher Thales of Miletus, who lived from about 625 BC to most 545 BC.^[five] The ancient Indian medical text Sushruta Samhita describes using magnetite to remove arrows embedded in a person's body.^[6]

In ancient Prc, the earliest literary reference to magnetism lies in a fourth-century BC book named afterward its author, Guiguzi.^[7] The 2nd-century BC annals, Lüshi Chunqiu, besides notes: "The lodestone makes atomic number 26 approach; some (force) is attracting it."^[viii] The earliest mention of the attraction of a needle is in a 1st-century work Lunheng (Balanced Inquiries): "A lodestone attracts a needle."^[nine] The 11th-century Chinese scientist Shen Kuo was the first person to write—in the Dream Pool Essays—of the magnetic needle compass and that information technology improved the accuracy of navigation by employing the astronomical concept of true north. By the 12th century, the Chinese were known to utilize the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such a mode that the handle of the spoon always pointed south.

Alexander Neckam, past 1187, was the first in Europe to describe the compass and its utilize for navigation. In 1269, Peter Peregrinus de Maricourt wrote the Epistola de magnete, the outset extant treatise describing the properties of magnets. In 1282, the properties of magnets and the dry out compasses were discussed past Al-Ashraf Umar II, a Yemeni physicist, astronomer, and geographer.^[x]

Leonardo Garzoni's but extant work, the Due trattati sopra la natura, e le qualità della calamita, is the first known example of a modernistic treatment of magnetic phenomena. Written in years near 1580 and never published, the treatise had a broad diffusion. In particular, Garzoni is referred to equally an expert in magnetism past Niccolò Cabeo, whose Philosophia Magnetica (1629) is just a re-adjustment of Garzoni's work. Garzoni'due south treatise was known also to Giovanni Battista Della Porta.

In 1600, William Gilbert published his De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet and Magnetic Bodies, and on the Great Magnet the Globe). In this piece of work he describes many of his experiments with his model earth called the terrella. From his experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses pointed n (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass).

An understanding of the relationship between electricity and magnetism began in 1819 with work by Hans Christian Ørsted, a professor at the Academy of Copenhagen, who discovered by the accidental twitching of a compass needle near a wire that an electric current could create a magnetic field. This landmark experiment is known equally Ørsted's Experiment. Several other experiments followed, with André-Marie Ampère, who in 1820 discovered that the magnetic field circulating in a closed-path was related to the electric current flowing through a surface enclosed by the path; Carl Friedrich Gauss; Jean-Baptiste British indian ocean territory and Félix Savart, both of whom in 1820 came up with the Biot–Savart law giving an equation for the magnetic field from a current-carrying wire; Michael Faraday, who in 1831 found that a time-varying magnetic flux through a loop of wire induced a voltage, and others finding farther links between magnetism and electricity. James Clerk Maxwell synthesized and expanded these insights into Maxwell'south equations, unifying electricity, magnetism, and optics into the field of electromagnetism. In 1905, Albert Einstein used these laws in motivating his theory of special relativity,^[xi] requiring that the laws held true in all inertial reference frames.

Electromagnetism has continued to develop into the 21st century, being incorporated into the more than fundamental theories of judge theory, quantum electrodynamics, electroweak theory, and finally the standard model.

Sources [edit]

Magnetism, at its root, arises from 2 sources:

1. Electric current.
2. Spin magnetic moments of elementary particles.

The magnetic backdrop of materials are mainly due to the magnetic moments of their atoms' orbiting electrons. The magnetic moments of the nuclei of atoms are typically thousands of times smaller than the electrons' magnetic moments, and then they are negligible in the context of the magnetization of materials. Nuclear magnetic moments are notwithstanding very important in other contexts, especially in nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI).

Ordinarily, the enormous number of electrons in a material are arranged such that their magnetic moments (both orbital and intrinsic) abolish 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), and combining into filled subshells with zero cyberspace orbital motion. In both cases, the electrons preferentially adopt arrangements in which the magnetic moment of each electron is canceled by the opposite moment of another electron. Moreover, fifty-fifty 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 volition contribute magnetic moments that point in different, random directions so that the material will not be magnetic.

Sometimes, either spontaneously, or owing to an applied external magnetic field—each of the electron magnetic moments will be, on average, lined up. A suitable textile can then produce a strong net magnetic field.

The magnetic beliefs of a material depends on its structure, peculiarly its electron configuration, for the reasons mentioned higher up, and as well on the temperature. At high temperatures, random thermal motion makes it more than difficult for the electrons to maintain alignment.

Types of magnetism [edit]

Hierarchy of types of magnetism.^[12]

Diamagnetism [edit]

Diamagnetism appears in all materials and is the tendency of a cloth to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field. Yet, in a material with paramagnetic properties (that is, with a tendency to enhance an external magnetic field), the paramagnetic behavior dominates.^[xiii] Thus, despite its universal occurrence, diamagnetic behavior is observed only in a purely diamagnetic fabric. In a diamagnetic cloth, there are no unpaired electrons, and so the intrinsic electron magnetic moments cannot produce any bulk result. 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 volition experience, in addition to their Coulomb allure to the nucleus, a Lorentz force from the magnetic field. Depending on which direction the electron is orbiting, this forcefulness may increase the centripetal forcefulness on the electrons, pulling them in towards the nucleus, or it may decrease the force, pulling them away from the nucleus. This issue systematically increases the orbital magnetic moments that were aligned contrary the field and decreases the ones aligned parallel to the field (in accordance with Lenz'due south law). This results in a small-scale bulk magnetic moment, with an contrary direction to the practical field.

This clarification is meant just as a heuristic; the Bohr–Van Leeuwen theorem shows that diamagnetism is impossible co-ordinate to classical physics, and that a proper understanding requires a breakthrough-mechanical clarification.

All materials undergo this orbital response. Yet, in paramagnetic and ferromagnetic substances, the diamagnetic outcome is overwhelmed by the much stronger effects caused by the unpaired electrons.

Paramagnetism [edit]

In a paramagnetic cloth at that place are unpaired electrons; i.due east., atomic or molecular orbitals with exactly one electron in them. While paired electrons are required by the Pauli exclusion principle to have their intrinsic ('spin') magnetic moments pointing in opposite directions, causing their magnetic fields to cancel out, an unpaired electron is free to align its magnetic moment in any management. 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.

Ferromagnetism [edit]

A ferromagnet, like a paramagnetic substance, has unpaired electrons. However, in improver to the electrons' intrinsic magnetic moment's trend to be parallel to an practical field, there is also in these materials a tendency for these magnetic moments to orient parallel to each other to maintain a lowered-free energy state. Thus, even in the absenteeism of an practical field, the magnetic moments of the electrons in the textile spontaneously line up parallel to 1 another.

Every ferromagnetic substance has its own individual temperature, called the Curie temperature, or Curie betoken, to a higher place which it loses its ferromagnetic properties. This is because the thermal tendency to disorder overwhelms the free energy-lowering due to ferromagnetic club.

Ferromagnetism but occurs in a few substances; common ones are fe, nickel, cobalt, their alloys, and some alloys of rare-earth metals.

Magnetic domains [edit]

Magnetic domains boundaries (white lines) in ferromagnetic material (blackness rectangle)

Effect of a magnet on the domains

The magnetic moments of atoms in a ferromagnetic textile cause them to behave something like tiny permanent magnets. They stick together and align themselves into modest regions of more or less uniform alignment chosen magnetic domains or Weiss domains. Magnetic domains tin be observed with a magnetic force microscope to reveal magnetic domain boundaries that resemble white lines in the sketch. There are many scientific experiments that can physically show magnetic fields.

When a domain contains also many molecules, it becomes unstable and divides into two domains aligned in opposite directions, then 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 (dotted yellow area), every bit shown at the left. When the magnetizing field is removed, the domains may not return to an unmagnetized state. This results in the ferromagnetic material's being magnetized, forming a permanent magnet.

When magnetized strongly plenty that the prevailing domain overruns all others to outcome in only ane unmarried domain, the textile 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 finish. When the material is cooled, this domain alignment construction spontaneously returns, in a manner roughly analogous to how a liquid can freeze into a crystalline solid.

Antiferromagnetism [edit]

Antiferromagnetic ordering

In an antiferromagnet, unlike a ferromagnet, there is a tendency for the intrinsic magnetic moments of neighboring valence electrons to bespeak in opposite directions. When all atoms are bundled in a substance so that each neighbor is anti-parallel, the substance is antiferromagnetic. Antiferromagnets have a zero internet magnetic moment, meaning that no field is produced by them. Antiferromagnets are less common compared to the other types of behaviors and are by and large observed at low temperatures. In varying temperatures, antiferromagnets can exist seen to exhibit diamagnetic and ferromagnetic backdrop.

In some materials, neighboring electrons adopt to point in opposite directions, simply in that location is no geometrical arrangement in which each pair of neighbors is anti-aligned. This is chosen a spin drinking glass and is an instance of geometrical frustration.

Ferrimagnetism [edit]

Like ferromagnetism, ferrimagnets retain their magnetization in the absence of a field. However, like antiferromagnets, neighboring pairs of electron spins tend to signal in opposite directions. These two backdrop are not contradictory, because in the optimal geometrical arrangement, in that location is more magnetic moment from the sublattice of electrons that point in one direction, than from the sublattice that points in the opposite direction.

Most ferrites are ferrimagnetic. The outset discovered magnetic substance, magnetite, is a ferrite and was originally believed to exist a ferromagnet; Louis Néel disproved this, notwithstanding, later discovering ferrimagnetism.

Superparamagnetism [edit]

Magnetic orders: comparison between ferro, antiferro and ferrimagnetism

When a ferromagnet or ferrimagnet is sufficiently small, information technology acts like a single magnetic spin that is subject to Brownian motion. Its response to a magnetic field is qualitatively similar to the response of a paramagnet, just much larger.

Other types of magnetism [edit]

• Metamagnetism
• Molecule-based magnets
• Single-molecule magnet
• Spin glass

Electromagnet [edit]

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

An electromagnet is a type of magnet in which the magnetic field is produced by an electric current.^[fourteen] The magnetic field disappears when the electric current is turned off. Electromagnets usually consist of a large number of closely spaced turns of wire that create the magnetic field. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.

The main advantage of an electromagnet over a permanent magnet is that the magnetic field can exist quickly changed by controlling the amount of electrical electric current in the winding. However, unlike a permanent magnet that needs no ability, an electromagnet requires a continuous supply of current to maintain the magnetic field.

Electromagnets are widely used as components of other electrical devices, such as motors, generators, relays, solenoids, loudspeakers, difficult disks, MRI machines, scientific instruments, and magnetic separation equipment. Electromagnets are too employed in industry for picking upwards and moving heavy iron objects such every bit flake iron and steel.^[xv] Electromagnetism was discovered in 1820.^[xvi]

Magnetism, electricity, and special relativity [edit]

As a event of Einstein's theory of special relativity, electricity and magnetism are fundamentally interlinked. Both magnetism lacking electricity, and electricity without magnetism, are inconsistent with special relativity, due to such effects as length wrinkle, fourth dimension dilation, and the fact that the magnetic forcefulness is velocity-dependent. However, when both electricity and magnetism are taken into business relationship, the resulting theory (electromagnetism) is fully consequent with special relativity.^{[11] [17]} In detail, a phenomenon that appears purely electric or purely magnetic to one observer may exist a mix of both to another, or more generally the relative contributions of electricity and magnetism are dependent on the frame of reference. Thus, special relativity "mixes" electricity and magnetism into a single, inseparable miracle called electromagnetism, analogous to how general relativity "mixes" space and time into spacetime.

All observations on electromagnetism apply to what might be considered to be primarily magnetism, e.yard. perturbations in the magnetic field are necessarily accompanied by a nonzero electric field, and propagate at the speed of lite.^{[ citation needed ]}

Magnetic fields in a cloth [edit]

In a vacuum,

${\displaystyle \mathbf {B} \ =\ \mu _{0}\mathbf {H} ,}$

where μ ₀ is the vacuum permeability.

In a textile,

${\displaystyle \mathbf {B} \ =\ \mu _{0}(\mathbf {H} +\mathbf {M} ).\ }$

The quantity μ ₀ M is called magnetic polarization.

If the field H is pocket-size, the response of the magnetization M in a diamagnet or paramagnet is approximately linear:

${\displaystyle \mathbf {G} =\chi \mathbf {H} ,}$

the abiding of proportionality existence called the magnetic susceptibility. If so,

${\displaystyle \mu _{0}(\mathbf {H} +\mathbf {M} )\ =\ \mu _{0}(i+\chi )\mathbf {H} \ =\ \mu _{r}\mu _{0}\mathbf {H} \ =\ \mu \mathbf {H} .}$

In a difficult magnet such as a ferromagnet, Thou is not proportional to the field and is generally nonzero even when H is nix (see Remanence).

Magnetic force [edit]

Magnetic lines of force of a bar magnet shown past fe filings on paper

Detecting magnetic field with compass and with iron filings

The miracle of magnetism is "mediated" by the magnetic field. An electric current or magnetic dipole creates a magnetic field, and that field, in plough, imparts magnetic forces on other particles that are in the fields.

Maxwell'south equations, which simplify to the Biot–Savart law in the case of steady currents, draw the origin and behavior of the fields that govern these forces. Therefore, magnetism is seen whenever electrically charged particles are in motion—for example, from motion of electrons in an electric current, or in certain cases from the orbital motility of electrons around an atom's nucleus. They as well arise from "intrinsic" magnetic dipoles arising from quantum-mechanical spin.

The same situations that create magnetic fields—charge moving in a current or in an atom, and intrinsic magnetic dipoles—are also the situations in which a magnetic field has an effect, creating a force. Following is the formula for moving charge; for the forces on an intrinsic dipole, see magnetic dipole.

When a charged particle moves through a magnetic field B, it feels a Lorentz strength F given by the cross production:^[18]

${\displaystyle \mathbf {F} =q(\mathbf {v} \times \mathbf {B} )}$

where

${\displaystyle q}$ is the electrical charge of the particle, and

v is the velocity vector of the particle

Because this is a cross product, the force is perpendicular to both the motion of the particle and the magnetic field. It follows that the magnetic force does no work on the particle; it may change the direction of the particle's movement, but it cannot crusade it to speed upwards or boring downwardly. The magnitude of the strength is

${\displaystyle F=qvB\sin \theta \,}$

where ${\displaystyle \theta }$ is the angle between v and B.

One tool for determining the management of the velocity vector of a moving charge, the magnetic field, and the force exerted is labeling the index finger "V"^{[ dubious – hash out ]}, the eye finger "B", and the thumb "F" with your correct hand. When making a gun-similar configuration, with the middle finger crossing under the alphabetize finger, the fingers represent the velocity vector, magnetic field vector, and force vector, respectively. See also correct-manus rule.

Magnetic dipoles [edit]

A very mutual source of magnetic field institute in nature is a dipole, with a "S pole" and a "North pole", terms dating dorsum to the use of magnets as compasses, interacting with the Globe'south magnetic field to indicate North and S on the globe. Since opposite ends of magnets are attracted, the north pole of a magnet is attracted to the due south pole of another magnet. The Earth'due south North Magnetic Pole (currently in the Arctic Ocean, due north of Canada) is physically a south pole, as it attracts the north pole of a compass. A magnetic field contains energy, and concrete systems move toward configurations with lower free energy. When diamagnetic material is placed in a magnetic field, a magnetic dipole tends to marshal itself in opposed polarity to that field, thereby lowering the net field strength. When ferromagnetic textile is placed within a magnetic field, the magnetic dipoles align to the applied field, thus expanding the domain walls of the magnetic domains.

Magnetic monopoles [edit]

Since a bar magnet gets its ferromagnetism from electrons distributed evenly throughout the bar, when a bar magnet is cut in one-half, each of the resulting pieces is a smaller bar magnet. Even though a magnet is said to take a north pole and a south pole, these two poles cannot exist separated from each other. A monopole—if such a thing exists—would be a new and fundamentally dissimilar kind of magnetic object. It would human action equally an isolated due north pole, non attached to a south pole, or vice versa. Monopoles would acquit "magnetic accuse" coordinating to electric charge. Despite systematic searches since 1931, as of 2010^[update], they have never been observed, and could very well non exist.^[19]

Nevertheless, some theoretical physics models predict the existence of these magnetic monopoles. Paul Dirac observed in 1931 that, because electricity and magnetism show a sure symmetry, only as quantum theory predicts that individual positive or negative electric charges tin can be observed without the opposing accuse, isolated South or Northward magnetic poles should be observable. Using breakthrough theory Dirac showed that if magnetic monopoles exist, then one could explain the quantization of electric charge—that is, why the observed simple particles deport charges that are multiples of the charge of the electron.

Certain m unified theories predict the beingness of monopoles which, unlike uncomplicated particles, are solitons (localized energy packets). The initial results of using these models to estimate the number of monopoles created in the Large Bang contradicted cosmological observations—the monopoles would have been then plentiful and massive that they would take long since halted the expansion of the universe. However, the idea of inflation (for which this problem served equally a fractional motivation) was successful in solving this problem, creating models in which monopoles existed but were rare plenty to be consistent with current observations.^[20]

Units [edit]

SI [edit]

SI electromagnetism units v t due east
Symbol[21]	Proper noun of quantity	Unit of measurement name	Symbol	Base units
E	energy	joule	J	kg⋅g2⋅s−ii = C⋅V
Q	electric charge	coulomb	C	A⋅s
I	electric electric current	ampere	A	A (= W/5 = C/south)
J	electrical electric current density	ampere per square metre	A/m2	A⋅m−two
ΔV; Δφ; ε	potential difference; voltage; electromotive force	volt	V	J/C = kg⋅chiliad2⋅south−iii⋅A−one
R; Z; 10	electric resistance; impedance; reactance	ohm	Ω	Five/A = kg⋅thouii⋅due south−3⋅A−2
ρ	resistivity	ohm metre	Ω⋅yard	kg⋅m3⋅south−3⋅A−2
P	electric power	watt	W	Five⋅A = kg⋅m2⋅s−3
C	capacitance	farad	F	C/V = kg−1⋅m−ii⋅A2⋅sfour
Φ E	electric flux	volt metre	V⋅one thousand	kg⋅m3⋅s−three⋅A−1
E	electric field strength	volt per metre	V/m	N/C = kg⋅m⋅A−1⋅s−3
D	electric displacement field	coulomb per square metre	C/1000ii	A⋅southward⋅thousand−two
ε	permittivity	farad per metre	F/one thousand	kg−1⋅m−iii⋅A2⋅due southfour
χ east	electric susceptibility	(dimensionless)	i	1
1000; Y; B	conductance; admittance; susceptance	siemens	S	Ω−1 = kg−i⋅grand−2⋅southward3⋅Aii
κ, γ, σ	conductivity	siemens per metre	S/g	kg−1⋅m−3⋅s3⋅A2
B	magnetic flux density, magnetic induction	tesla	T	Wb/mii = kg⋅south−2⋅A−i = Northward⋅A−1⋅m−1
Φ, Φ M, Φ B	magnetic flux	weber	Wb	V⋅due south = kg⋅one thousandii⋅south−ii⋅A−1
H	magnetic field forcefulness	ampere per metre	A/m	A⋅1000−1
50, M	inductance	henry	H	Wb/A = V⋅s/A = kg⋅one thousand2⋅s−2⋅A−ii
μ	permeability	henry per metre	H/thousand	kg⋅thou⋅due south−ii⋅A−2
χ	magnetic susceptibility	(dimensionless)	1	1
µ	magnetic dipole moment	ampere square meter	A⋅chiliad2	A⋅mtwo = J⋅T−1 = x3 emu
σ	mass magnetization	ampere square meter per kilogram	A⋅m2/kg	A⋅gii⋅kg−i = emu⋅g−1 = erg⋅G−ane⋅g−1

Other [edit]

• gauss – the centimeter-gram-2d (CGS) unit of magnetic field (denoted B).
• oersted – the CGS unit of magnetizing field (denoted H)
• maxwell – the CGS unit for magnetic flux
• gamma – a unit of magnetic flux density that was commonly used before the tesla came into use (1.0 gamma = 1.0 nanotesla)
• μ ₀ – common symbol for the permeability of costless space (4π × ten⁻⁷ newton/(ampere-plow)ⁱⁱ)

Living things [edit]

Some organisms can detect magnetic fields, a phenomenon known as magnetoception. Some materials in living things are ferromagnetic, though it is unclear if the magnetic backdrop serve a special function or are simply a byproduct of containing iron. For case, chitons, a blazon of marine mollusk, produce magnetite to harden their teeth, and fifty-fifty humans produce magnetite in bodily tissue.^[22] Magnetobiology studies the effects of magnetic fields on living organisms; fields naturally produced past an organism are known every bit biomagnetism. Many biological organisms are mostly made of h2o, and because water is diamagnetic, extremely potent magnetic fields can repel these living things.

Quantum-mechanical origin of magnetism [edit]

While heuristic explanations based on classical physics tin be formulated, diamagnetism, paramagnetism and ferromagnetism tin can be fully explained only using quantum theory.^{[23] [24]} A successful model was developed already in 1927, by Walter Heitler and Fritz London, who derived, quantum-mechanically, how hydrogen molecules are formed from hydrogen atoms, i.east. from the atomic hydrogen orbitals ${\displaystyle u_{A}}$ and ${\displaystyle u_{B}}$ centered at the nuclei A and B, run into below. That this leads to magnetism is not at all obvious, but will be explained in the following.

Co-ordinate to the Heitler–London theory, so-called two-body molecular ${\displaystyle \sigma }$ -orbitals are formed, namely the resulting orbital is:

${\displaystyle \psi (\mathbf {r} _{1},\,\,\mathbf {r} _{ii})={\frac {1}{\sqrt {2}}}\,\,\left(u_{A}(\mathbf {r} _{1})u_{B}(\mathbf {r} _{two})+u_{B}(\mathbf {r} _{i})u_{A}(\mathbf {r} _{two})\right)}$

Here the last product means that a offset electron, r ₁, is in an atomic hydrogen-orbital centered at the 2nd nucleus, whereas the 2nd electron runs around the first nucleus. This "exchange" phenomenon is an expression for the quantum-mechanical property that particles with identical properties cannot be distinguished. Information technology is specific not only for the formation of chemical bonds, but likewise for magnetism. That is, in this connexion the term substitution interaction arises, a term which is essential for the origin of magnetism, and which is stronger, roughly by factors 100 and even past k, than the energies arising from the electrodynamic dipole-dipole interaction.

As for the spin function ${\displaystyle \chi (s_{i},s_{2})}$ , which is responsible for the magnetism, we take the already mentioned Pauli's principle, namely that a symmetric orbital (i.e. with the + sign as above) must be multiplied with an antisymmetric spin function (i.eastward. with a − sign), and vice versa. Thus:

${\displaystyle \chi (s_{i},\,\,s_{two})={\frac {i}{\sqrt {ii}}}\,\,\left(\alpha (s_{one})\beta (s_{ii})-\beta (s_{1})\alpha (s_{2})\right)}$ ,

I.e., not only ${\displaystyle u_{A}}$ and ${\displaystyle u_{B}}$ must be substituted by α and β, respectively (the offset entity means "spin upwardly", the second one "spin down"), but besides the sign + by the − sign, and finally r _i by the discrete values southward _i (= ±½); thereby we have ${\displaystyle \alpha (+1/ii)=\beta (-1/2)=1}$ and ${\displaystyle \alpha (-ane/2)=\beta (+ane/ii)=0}$ . The "singlet land", i.due east. the − sign, ways: the spins are antiparallel, i.eastward. for the solid we have antiferromagnetism, and for two-atomic molecules one has diamagnetism. The tendency to grade a (homoeopolar) chemic bond (this means: the formation of a symmetric molecular orbital, i.e. with the + sign) results through the Pauli principle automatically in an antisymmetric spin state (i.due east. with the − sign). In contrast, the Coulomb repulsion of the electrons, i.e. the tendency that they try to avoid each other by this repulsion, would lead to an antisymmetric orbital function (i.e. with the − sign) of these ii particles, and complementary to a symmetric spin function (i.e. with the + sign, one of the and then-called "triplet functions"). Thus, at present the spins would be parallel (ferromagnetism in a solid, paramagnetism in two-atomic gases).

The concluding-mentioned tendency dominates in the metals iron, cobalt and nickel, and in some rare earths, which are ferromagnetic. Nigh of the other metals, where the outset-mentioned tendency dominates, are nonmagnetic (e.g. sodium, aluminium, and magnesium) or antiferromagnetic (east.g. manganese). Diatomic gases are also almost exclusively diamagnetic, and non paramagnetic. Nevertheless, the oxygen molecule, because of the involvement of π-orbitals, is an exception important for the life-sciences.

The Heitler-London considerations can exist generalized to the Heisenberg model of magnetism (Heisenberg 1928).

The explanation of the phenomena is thus essentially based on all subtleties of breakthrough mechanics, whereas the electrodynamics covers mainly the phenomenology.

See also [edit]

• Coercivity
• Gravitomagnetism
• Magnetic hysteresis
• Magnetar
• Magnetic bearing
• Magnetic circuit
• Magnetic cooling
• Magnetic field viewing film
• Magnetic stirrer
• Magnetic construction
• Magnetism and temperature
• Micromagnetism
• Neodymium magnet
• Plastic magnet
• Rare-world magnet
• Spin wave
• Spontaneous magnetization
• Vibrating-sample magnetometer

References [edit]

1. ^ Jiles, David (2 September 2015). Introduction to magnetism and magnetic materials (Third ed.). Boca Raton. ISBN978-one-4822-3887-7. OCLC 909323904.
2. ^ Du Trémolet de Lacheisserie, Étienne; Damien Gignoux; Michel Schlenker (2005). Magnetism: Fundamentals. Springer. pp. three–6. ISBN978-0-387-22967-vi.
3. ^ Platonis Opera, Meyer and Zeller, 1839, p. 989.
4. ^ The location of Magnesia is debated; it could be the region in mainland Hellenic republic or Magnesia ad Sipylum. See, for example, "Magnet". Language Lid weblog. 28 May 2005. Retrieved 22 March 2013.
5. ^ Fowler, Michael (1997). "Historical Beginnings of Theories of Electricity and Magnetism". Retrieved 2008-04-02 .
6. ^ Kumar Goyal, Rajendra (2017). Nanomaterials and Nanocomposites: Synthesis, Properties, Characterization Techniques, and Applications. CRC Press. p. 171. ISBN9781498761673.
7. ^ The department "Fanying 2" (反應第二) of The Guiguzi: " 其察言也，不失若磁石之取鍼，舌之取燔骨 ".
8. ^ Li, Shu-hua (1954). "Origine de la Boussole Ii. Aimant et Boussole". Isis (in French). 45 (2): 175–196. doi:10.1086/348315. JSTOR 227361. S2CID 143585290. un passage dans le Liu-che-tch'ouen-ts'ieou [...]: "La pierre d'aimant fait venir le fer ou elle l'attire."
   From the section "Jingtong" ( 精通 ) of the "Almanac of the Terminal Autumn Month" ( 季秋紀 ): " 慈石召鐵，或引之也 ]"
9. ^ In the section "A Last Word on Dragons" ( 亂龍篇 Luanlong) of the Lunheng: "Amber takes upwards straws, and a load-stone attracts needles" ( 頓牟掇芥，磁石引針 ).
10. ^ Schmidl, Petra K. (1996–1997). "Ii Early Arabic Sources On The Magnetic Compass". Journal of Arabic and Islamic Studies. 1: 81–132.
11. ^ ^{a b} A. Einstein: "On the Electrodynamics of Moving Bodies", June 30, 1905.
12. ^ HP Meyers (1997). Introductory solid country physics (two ed.). CRC Press. p. 362; Figure 11.1. ISBN9781420075021.
13. ^ Catherine Westbrook; Carolyn Kaut; Carolyn Kaut-Roth (1998). MRI (Magnetic Resonance Imaging) in practice (2 ed.). Wiley-Blackwell. p. 217. ISBN978-0-632-04205-0.
14. ^ Purcell 2012, p. 320,584
15. ^ Merzouki, Rochdi; Samantaray, Arun Kumar; Pathak, Pushparaj Mani (2012). Intelligent Mechatronic Systems: Modeling, Control and Diagnosis. Springer Science & Concern Media. pp. 403–405. ISBN978-1447146285.
16. ^ Sturgeon, Due west. (1825). "Improved Electro Magnetic Apparatus". Trans. Royal Gild of Arts, Manufactures, & Commerce. 43: 37–52. cited in Miller, T.J.East (2001). Electronic Control of Switched Reluctance Machines. Newnes. p. 7. ISBN978-0-7506-5073-1.
17. ^ Griffiths 1998, affiliate 12
18. ^ Jackson, John David (1999). Classical electrodynamics (3rd ed.). New York: Wiley. ISBN978-0-471-30932-1.
19. ^ Milton mentions some inconclusive events (p. threescore) and still concludes that "no evidence at all of magnetic monopoles has survived" (p.three). Milton, Kimball A. (June 2006). "Theoretical and experimental status of magnetic monopoles". Reports on Progress in Physics. 69 (half-dozen): 1637–1711. arXiv:hep-ex/0602040. Bibcode:2006RPPh...69.1637M. doi:10.1088/0034-4885/69/half-dozen/R02. S2CID 119061150. .
20. ^ Guth, Alan (1997). The Inflationary Universe: The Quest for a New Theory of Catholic Origins . Perseus. ISBN978-0-201-32840-0. OCLC 38941224. .
21. ^ International Matrimony of Pure and Applied Chemistry (1993). Quantities, Units and Symbols in Concrete Chemistry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. pp. fourteen–15. Electronic version.
22. ^ Kirschvink, Joseph L.; Kobayashi-Kirshvink, Atsuko; Diaz-Ricci, Juan C.; Kirschvink, Steven J. (1992). "Magnetite in Human Tissues: A Mechanism for the Biological Effects of Weak ELF Magnetic Fields" (PDF). Bioelectromagnetics Supplement. one: 101–113. doi:10.1002/bem.2250130710. PMID 1285705. Retrieved 29 March 2016.
23. ^ The magnetism of matter, Feynman Lectures in Physics Ch 34
24. ^ Ferromagnetism, Feynman Lectures in Physics Ch 36

Further reading [edit]

• David 1000. Cheng (1992). Field and Wave Electromagnetics. Addison-Wesley Publishing Visitor, Inc. ISBN978-0-201-12819-2.
• Furlani, Edward P. (2001). Permanent Magnet and Electromechanical Devices: Materials, Analysis and Applications. Bookish Press. ISBN978-0-12-269951-1. OCLC 162129430.
• Griffiths, David J. (1998). Introduction to Electrodynamics (3rd ed.) . Prentice Hall. ISBN978-0-13-805326-0. OCLC 40251748.
• Kronmüller, Helmut. (2007). Handbook of Magnetism and Advanced Magnetic Materials, 5 Volume Set. John Wiley & Sons. ISBN978-0-470-02217-7. OCLC 124165851.
• Purcell, Edward 1000. (2012). Electricity and magnetism (3rd ed.). Cambridge: Cambridge Univ. Press. ISBN9781-10701-4022.
• Tipler, Paul (2004). Physics for Scientists and Engineers: Electricity, Magnetism, Lite, and Elementary Modern Physics (5th ed.). W.H. Freeman. ISBN978-0-7167-0810-0. OCLC 51095685.

Bibliography [edit]

• The Exploratorium Science Snacks – Subject:Physics/Electricity & Magnetism
• A drove of magnetic structures – MAGNDATA

robertstrok1973.blogspot.com

Source: https://en.wikipedia.org/wiki/Magnetism

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