Electromagnetism

From Wikipedia, the chargeless encyclopedia
(Redirected from Electromagnetic force)
This COMMODITY includes a account of references, but its sources abide cryptic because it has bereft inline citations. Please advice to advance this commodity by introducing added absolute citations. (November 2012)
Electromagnetism
Solenoid
Electricity Magnetism
Electrostatics[show]
Magnetostatics[show]
Electrodynamics[hide]
Lorentz force law
Electromagnetic induction
Faraday's law
Lenz's law Displacement current
Maxwell's equations
Electromagnetic field
Electromagnetic radiation
Maxwell tensor Poynting vector
Liénard–Wiechert potential
Jefimenko's equations
Eddy current
London equations
Electrical network[show]
Covariant formulation[show]
Scientists[show]
v t e
Electromagnetism, or the electromagnetic force is one of the four axiological interactions in nature, the added three getting the able interaction, the anemic interaction, and gravitation. This force is declared by electromagnetic fields, and has innumerable concrete instances including the alternation of electrically answerable particles and the alternation of uncharged alluring force fields with electrical conductors.
The chat electromagnetism is a admixture anatomy of two Greek terms, бјўО»ОµОєП„ПЃОїОЅ, Д“lektron, "amber", and ОјО±ОіОЅО®П„О·П‚, magnetic, from "magnГ­tis lГ­thos" (ОјО±ОіОЅО®П„О·П‚ О»ОЇОёОїП‚), which agency "magnesian stone", a blazon of adamant ore. The science of electromagnetic phenomena is authentic in agreement of the electromagnetic force, sometimes alleged the Lorentz force, which includes both electricity and allure as elements of one phenomenon.
During the quark epoch, the electroweak force breach into the electromagnetic and anemic force. The electromagnetic force plays a above role in free the centralized backdrop of a lot of altar encountered in circadian life. Ordinary amount takes its anatomy as a aftereffect of intermolecular armament amid alone molecules in matter. Electrons are apprenticed by electromagnetic beachcomber mechanics into orbitals about diminutive nuclei to anatomy atoms, which are the architecture blocks of molecules. This governs the processes complex in chemistry, which appear from interactions amid the electrons of adjoining atoms, which are in about-face bent by the alternation amid electromagnetic force and the drive of the electrons.
There are abundant algebraic descriptions of the electromagnetic field. In classical electrodynamics, electric fields are declared as electric abeyant and electric accepted in Ohm's law, alluring fields are associated with electromagnetic consecration and magnetism, and Maxwell's equations call how electric and alluring fields are generated and adapted by anniversary added and by accuse and currents.
The abstract implications of electromagnetism, in accurate the enactment of the acceleration of ablaze based on backdrop of the "medium" of advancement (permeability and permittivity), led to the development of appropriate relativity by Albert Einstein in 1905.
Contents [hide]
1 History of the theory
2 Overview
3 Classical electrodynamics
4 Photoelectric effect
5 Quantities and units
6 Electromagnetic phenomena
7 Electromagnetic induction
8 Electromagnetic surveys
9 See also
10 Notes
11 Further reading
11.1 Web sources
11.2 Lecture notes
11.3 Textbooks
11.4 General references
12 External links

History of the theory

See also: History of electromagnetic theory
Originally electricity and allure were anticipation of as two abstracted forces. This appearance changed, however, with the advertisement of James Clerk Maxwell's 1873 Treatise on Electricity and Allure in which the interactions of absolute and abrogating accuse were apparent to be adapted by one force. There are four capital furnishings consistent from these interactions, all of which accept been acutely approved by experiments:
Electric accuse allure or repel one addition with a force inversely proportional to the aboveboard of the ambit amid them: clashing accuse attract, like ones repel.
Magnetic poles (or states of animosity at alone points) allure or repel one addition in a agnate way and consistently appear in pairs: every arctic pole is acclimatized to a south pole.
An electric accepted in a wire creates a annular alluring acreage about the wire, its administration (clockwise or counter-clockwise) depending on that of the current.
A accepted is induced in a bend of wire if it is confused appear or abroad from a alluring field, or a allurement is confused appear or abroad from it, the administration of accepted depending on that of the movement.

AndrГ©-Marie AmpГЁre
While advancing for an black address on 21 April 1820, Hans Christian Г˜rsted fabricated a hasty observation. As he was ambience up his materials, he noticed a ambit aggravate deflected from alluring arctic if the electric accepted from the array he was application was switched on and off. This angle assertive him that alluring fields afford from all abandon of a wire accustomed an electric current, just as ablaze and calefaction do, and that it accepted a absolute accord amid electricity and magnetism.


Michael Faraday
At the time of discovery, Г˜rsted did not advance any satisfactory annual of the phenomenon, nor did he try to represent the abnormality in a algebraic framework. However, three months after he began added accelerated investigations. Soon thereafter he appear his findings, proving that an electric accepted produces a alluring acreage as it flows through a wire. The CGS assemblage of alluring consecration (oersted) is alleged in annual of his contributions to the acreage of electromagnetism.


James Clerk Maxwell
His allegation resulted in accelerated analysis throughout the accurate association in electrodynamics. They afflicted French physicist AndrГ©-Marie AmpГЁre's developments of a individual algebraic anatomy to represent the alluring armament amid current-carrying conductors. Г˜rsted's analysis aswell represented a above footfall against a unified abstraction of energy.
This unification, which was empiric by Michael Faraday, continued by James Clerk Maxwell, and partially reformulated by Oliver Heaviside and Heinrich Hertz, is one of the key accomplishments of 19th aeon algebraic physics. It had extensive consequences, one of which was the compassionate of the attributes of light. Clashing what was proposed in Electromagnetism, ablaze and added electromagnetic after-effects are at the present apparent as demography the anatomy of quantized, self-propagating oscillatory electromagnetic acreage disturbances which accept been alleged photons. Altered frequencies of cadence accord acceleration to the altered forms of electromagnetic radiation, from radio after-effects at the everyman frequencies, to arresting ablaze at average frequencies, to gamma application at the accomplished frequencies.
Г˜rsted was not the alone being to appraise the affiliation amid electricity and magnetism. In 1802 Gian Domenico Romagnosi, an Italian acknowledged scholar, deflected a alluring aggravate by electrostatic charges. Actually, no active accepted existed in the bureaucracy and appropriately no electromagnetism was present. An annual of the analysis was appear in 1802 in an Italian newspaper, but it was abundantly disregarded by the abreast accurate community.[1]

Overview

The electromagnetic force is one of the four accepted axiological forces. The added axiological armament are:
the anemic nuclear force, which binds to all accepted particles in the Standard Model, and causes assertive forms of radioactive decay. (In atom physics though, the electroweak alternation is the unified description of two of the four accepted axiological interactions of nature: electromagnetism and the anemic interaction);
the able nuclear force, which binds quarks to anatomy nucleons, and binds nucleons to anatomy nuclei
the gravitational force.
All added armament (e.g., friction) are ultimately acquired from these axiological armament and drive agitated by the movement of particles.
The electromagnetic force is the one amenable for about all the phenomena one encounters in circadian activity aloft the nuclear scale, with the barring of gravity. Roughly speaking, all the armament complex in interactions amid atoms can be explained by the electromagnetic force acting on the electrically answerable diminutive nuclei and electrons central and about the atoms, calm with how these particles backpack drive by their movement. This includes the armament we acquaintance in "pushing" or "pulling" accustomed actual objects, which appear from the intermolecular armament amid the alone molecules in our bodies and those in the objects. It aswell includes all forms of actinic phenomena.
A all-important allotment of compassionate the intra-atomic to intermolecular armament is the able force generated by the drive of the electrons' movement, and that electrons move amid interacting atoms, accustomed drive with them. As a accumulating of electrons becomes added confined, their minimum drive necessarily increases due to the Pauli exclusion principle. The behaviour of amount at the atomic calibration including its body is bent by the antithesis amid the electromagnetic force and the force generated by the barter of drive agitated by the electrons themselves.

Classical electrodynamics

Main article: Classical electrodynamics
The scientist William Gilbert proposed, in his De Magnete (1600), that electricity and magnetism, while both able of causing allure and abhorrence of objects, were audible effects. Mariners had noticed that lightning strikes had the adeptness to afflict a ambit needle, but the hotlink amid lightning and electricity was not accepted until Benjamin Franklin's proposed abstracts in 1752. One of the aboriginal to ascertain and broadcast a hotlink amid counterfeit electric accepted and allure was Romagnosi, who in 1802 noticed that abutting a wire beyond a voltaic accumulation deflected a adjacent ambit needle. However, the aftereffect did not become broadly accepted until 1820, if Г˜rsted performed a agnate experiment.[2] Г˜rsted's plan afflicted AmpГЁre to aftermath a approach of electromagnetism that set the accountable on a algebraic foundation.
A approach of electromagnetism, accepted as classical electromagnetism, was developed by assorted physicists over the advance of the 19th century, culminating in the plan of James Clerk Maxwell, who unified the above-mentioned developments into a individual approach and apparent the electromagnetic attributes of light. In classical electromagnetism, the electromagnetic acreage obeys a set of equations accepted as Maxwell's equations, and the electromagnetic force is accustomed by the Lorentz force law.
One of the peculiarities of classical electromagnetism is that it is difficult to accommodate with classical mechanics, but it is accordant with appropriate relativity. According to Maxwell's equations, the acceleration of ablaze in a exhaustion is a accepted constant, abased alone on the electrical permittivity and alluring permeability of chargeless space. This violates Galilean invariance, a abiding cornerstone of classical mechanics. One way to ACCOMMODATE THE two theories (electromagnetism and classical mechanics) is to accept the actuality of a luminiferous aether through which the ablaze propagates. However, consecutive beginning efforts bootless to ascertain the attendance of the aether. After important contributions of Hendrik Lorentz and Henri PoincarГ©, in 1905, Albert Einstein apparent the botheration with the accession of appropriate relativity, which replaces classical kinematics with a new approach of kinematics that is accordant with classical electromagnetism. (For added information, see History of appropriate relativity.)
In addition, relativity approach shows that in affective frames of advertence a alluring acreage transforms to a acreage with a nonzero electric basic and carnality versa; appropriately durably assuming that they are two abandon of the aforementioned coin, and appropriately the appellation "electromagnetism". (For added information, see Classical electromagnetism and appropriate relativity and Covariant conception of classical electromagnetism.

Photoelectric effect

Main article: Photoelectric effect
In addition cardboard appear in that aforementioned year, Albert Einstein debilitated the actual foundations of classical electromagnetism. In his approach of the photoelectric aftereffect (for which he won the Nobel cost in physics) and aggressive by the abstraction of Max Planck's "quanta", he posited that ablaze could abide in detached particle-like quantities as well, which after came to be accepted as photons. Einstein's approach of the photoelectric aftereffect continued the insights that appeared in the band-aid of the ultraviolet accident presented by Max Planck in 1900. In his work, Planck showed that hot altar afford electromagnetic radiation in detached packets ("quanta"), which leads to a bound absolute activity emitted as atramentous physique radiation. Both of these after-effects were in absolute bucking with the classical appearance of ablaze as a connected wave. Planck's and Einstein's theories were ancestors of breakthrough mechanics, which, if formulated in 1925, apprenticed the apparatus of a breakthrough approach of electromagnetism. This theory, completed in the 1940s-1950s, is accepted as breakthrough electrodynamics (or "QED"), and, in situations area perturbation approach is applicable, is one of the a lot of authentic theories accepted to physics.

Quantities and units

See also: List of concrete quantities and List of electromagnetism equations
Electromagnetic units are allotment of a arrangement of electrical units based primarily aloft the alluring backdrop of electric currents, the axiological SI assemblage getting the ampere. The units are:
ampere (electric current)
coulomb (electric charge)
farad (capacitance)
henry (inductance)
ohm (resistance)
tesla (magnetic alteration density)
volt (electric potential)
watt (power)
weber (magnetic flux)
In the electromagnetic cgs system, electric accepted is a axiological abundance authentic via AmpГЁre's law and takes the permeability as a dimensionless abundance (relative permeability) whose amount in a exhaustion is unity. As a consequence, the aboveboard of the acceleration of ablaze appears absolutely in some of the equations commutual quantities in this system.
SI electromagnetism units v t e
Symbol[3] Name of Quantity Derived Units Unit Base Units
I electric current ampere (SI abject unit) A A (= W/V = C/s)
Q electric charge coulomb C Aв‹…s
U, О”V, О”П†; E potential difference; electromotive force volt V kgв‹…m2в‹…sв€’3в‹…Aв€’1 (= J/C)
R; Z; X electric resistance; impedance; reactance ohm О© kgв‹…m2в‹…sв€’3в‹…Aв€’2 (= V/A)
ПЃ resistivity ohm metre О©в‹…m kgв‹…m3в‹…sв€’3в‹…Aв€’2
P electric power watt W kgв‹…m2в‹…sв€’3 (= Vв‹…A)
C capacitance farad F kgв€’1в‹…mв€’2в‹…s4в‹…A2 (= C/V)
E electric acreage strength volt per metre V/m kgв‹…mв‹…sв€’3в‹…Aв€’1 (= N/C)
D electric displacement field coulomb per aboveboard metre C/m2 Aв‹…sв‹…mв€’2
Оµ permittivity farad per metre F/m kgв€’1в‹…mв€’3в‹…s4в‹…A2
χe electric susceptibility (dimensionless) – –
G; Y; B conductance; admittance; susceptance siemens S kgв€’1в‹…mв€’2в‹…s3в‹…A2 (= О©в€’1)
Оє, Оі, Пѓ conductivity siemens per metre S/m kgв€’1в‹…mв€’3в‹…s3в‹…A2
B magnetic alteration density, alluring induction tesla T kgв‹…sв€’2в‹…Aв€’1 (= Wb/m2 = Nв‹…Aв€’1в‹…mв€’1)
\Phi magnetic flux weber Wb kgв‹…m2в‹…sв€’2в‹…Aв€’1 (= Vв‹…s)
H magnetic acreage strength ampere per metre A/m Aв‹…mв€’1
L, M inductance henry H kgв‹…m2в‹…sв€’2в‹…Aв€’2 (= Wb/A = Vв‹…s/A)
Ој permeability henry per metre H/m kgв‹…mв‹…sв€’2в‹…Aв€’2
χ magnetic susceptibility (dimensionless) – –
Formulas for concrete laws of electromagnetism (such as Maxwell's equations) charge to be adapted depending on what arrangement of units one uses. This is because there is no one-to-one accord amid electromagnetic units in SI and those in CGS, as is the case for automated units. Furthermore, aural CGS, there are several believable choices of electromagnetic units, arch to altered assemblage "sub-systems", including Gaussian, "ESU", "EMU", and Heaviside–Lorentz. Among these choices, Gaussian units are the a lot of accepted today, and in actuality the byword "CGS units" is generally acclimated to accredit accurately to CGS-Gaussian units.

Electromagnetic phenomena

With the barring of gravitation, electromagnetic phenomena as declared by breakthrough electrodynamics (which includes classical electrodynamics as a attached case) annual for about all concrete phenomena appreciable to the abandoned animal senses, including ablaze and added electromagnetic radiation, all of chemistry, a lot of of mechanics (excepting gravitation), and, of course, allure and electricity. Alluring monopoles (and "Gilbert" dipoles) are not carefully electromagnetic phenomena, back in accepted electromagnetism, alluring fields are generated not by accurate "magnetic charge" but by currents. There are, however, abridged amount analogs of alluring monopoles in alien abstracts (spin ice) created in the laboratory.[4]

Electromagnetic induction

Electromagnetic Induction is the Induction of an electromotive force in a ambit by capricious the alluring alteration affiliated with the circuit. The abnormality was aboriginal advised in 1830-31 by Joseph Henry and Michael Faraday, who apparent that if the alluring acreage about an electromagnet was added and decreased, an electric accepted should be detected by adjacent conductor. A accepted can aswell be induced by consistently affective a abiding allurement in and out of a braid of wire, or by consistently affective a aqueduct abreast a anchored abiding magnet. The induced electromotive force is proportional to the amount of change of the alluring alteration acid beyond the circuit.