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Electric and magnetic fields

It is often convenient to understand the electromagnetic field in terms of two separate fields: the electric field and the magnetic field. A non-zero electric field is produced by the presence of electrically charged particles, and gives rise to the electric electric current) in electrical conductors. The magnetic field, on the other hand, can be produced by the motion of electric charges, or electric current, and gives rise to the magnetic force associated with magnets.

The term "electromagnetism" comes from the fact that the electric and magnetic fields generally cannot be described independently of one another. A changing magnetic field produces an electric field (generator]]s, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field.

Because field, i.e., an electromagnetic wave. Different rays at the highest frequencies.

The theoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905.

The electromagnetic force

The force that the electromagnetic field exerts on electrically charged particles, called the electromagnetic force, is one of the four fundamental forces. The other fundamental forces are the strong nuclear force (which holds atomic nuclei together), the weak nuclear force (which causes certain forms of radioactive decay), and the gravitational force. All other forces are ultimately derived from these fundamental forces.

As it turns out, the electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life, with the exception of gravity. Roughly speaking, all the forces involved in interactions between atoms can be traced to the electromagnetic force acting on the electrically charged protons and electrons inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects. It also includes all forms of chemical phenomena, which arise from interactions between electron orbitals.

Origins of electromagnetic theory

The scientist William Gilbert proposed, in his De Magnete (1600), that the first to discover and publish a link between man-made electric current and magnetism was Romagnosi, who in 1802 noticed that connecting a wire across a Voltaic pile deflected a nearby compass needle. However, the effect did not become widely known until 1820, when Ørsted performed a similar experiment. Ørsted's work influenced Ampère to produce a theory of electromagnetism that set the subject on a mathematical foundation.

An accurate theory of electromagnetism, known as classical electromagnetism, was developed by various physicists over the course of the 19th century, culminating in the work of James Clerk Maxwell, who unified the preceding developments into a single theory and discovered the electromagnetic nature of light. In classical electromagnetism, the electromagnetic field obeys a set of equations known as Maxwell's equations, and the electromagnetic force is given by the Lorentz force law.

One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity. According to Maxwell's equations, the speed of light is a universal constant, dependent only on the electrical permittivity and magnetic permeability of the vacuum. This violates Galilean invariance, a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a luminiferous aether through which the . In 1905, Albert Einstein solved the problem with the introduction of special relativity, which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism.

In addition, Relativity theory shows that in moving frames of reference a magnetic field becomes an electrostatic field and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term Electromagnetism.

Failures of classical electromagnetism

In another paper published in that same year, Einstein undermined the very foundations of classical electromagnetism. His theory of the photoelectric effect (for which he won the Nobel prize for phcs) posited that light could exist in discrete particle-like quantities, which later came to be known as photons. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the ultraviolet catastrophe presented by Max Planck in 1900. In his work, Planck showed that hot objects emit electromagnetic radiation in discrete packets, which leads to a finite total energy emitted as black body radiation. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of quantum mechanics, which, when formulated in 1925, necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the 1940s, is known as quantum electrodynamics (or "QED"), and is one of the most accurate theories known to physics.

SI electricity units

SI electromagnetism units
v
t
e
Symbol^[1]	Name of quantity	Unit name	Symbol	Base units
$E$	energy	joule	J = C⋅V = W⋅s	kg⋅m²⋅s⁻²
$Q$	electric charge	coulomb	C	A⋅s
$I$	electric current	ampere	A = C/s = W/V	A
$J$	electric current density	ampere per square metre	A/m²	A⋅m⁻²
$U$ , $Δ V$ ; $Δ ϕ$ ; E, $ξ$	potential difference; voltage; electromotive force	volt	V = J/C	kg⋅m²⋅s⁻³⋅A⁻¹
$R$ ; $Z$ ; $X$	electric resistance; impedance; reactance	ohm	Ω = V/A	kg⋅m²⋅s⁻³⋅A⁻²
$ρ$	resistivity	ohm metre	Ω⋅m	kg⋅m³⋅s⁻³⋅A⁻²
$P$	electric power	watt	W = V⋅A	kg⋅m²⋅s⁻³
$C$	capacitance	farad	F = C/V	kg⁻¹⋅m⁻²⋅A²⋅s⁴
$Φ E$	electric flux	volt metre	V⋅m	kg⋅m³⋅s⁻³⋅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/m²	A⋅s⋅m⁻²
$ε$	permittivity	farad per metre	F/m	kg⁻¹⋅m⁻³⋅A²⋅s⁴
$χ e$	electric susceptibility	(dimensionless)	1	1
$p$	electric dipole moment	coulomb metre	C⋅m	A⋅s⋅m
$G$ ; $Y$ ; $B$	conductance; admittance; susceptance	siemens	S = Ω⁻¹	kg⁻¹⋅m⁻²⋅s³⋅A²
$κ$ , $γ$ , $σ$	conductivity	siemens per metre	S/m	kg⁻¹⋅m⁻³⋅s³⋅A²
$B$	magnetic flux density, magnetic induction	tesla	T = Wb/m² = N⋅A⁻¹⋅m⁻¹	kg⋅s⁻²⋅A⁻¹
$Φ$ , $Φ M$ , $Φ B$	magnetic flux	weber	Wb = V⋅s	kg⋅m²⋅s⁻²⋅A⁻¹
$H$	magnetic field strength	ampere per metre	A/m	A⋅m⁻¹
F	magnetomotive force	ampere	A = Wb/H	A
R	magnetic reluctance	inverse henry	H⁻¹ = A/Wb	kg⁻¹⋅m⁻²⋅s²⋅A²
P	magnetic permeance	henry	H = Wb/A	kg⋅m²⋅s^-2⋅A^-2
$L$ , $M$	inductance	henry	H = Wb/A = V⋅s/A	kg⋅m²⋅s⁻²⋅A⁻²
$μ$	permeability	henry per metre	H/m	kg⋅m⋅s⁻²⋅A⁻²
$χ$	magnetic susceptibility	(dimensionless)	1	1
$m$	magnetic dipole moment	ampere square meter	A⋅m² = J⋅T⁻¹	A⋅m²
$σ$	mass magnetization	ampere square meter per kilogram	A⋅m²/kg	A⋅m²⋅kg⁻¹

References

. ISBN 1572594926. {{cite book}}: Missing or empty |title= (help); Unknown parameter |Author= ignored (|author= suggested) (help); Unknown parameter |Publisher= ignored (|publisher= suggested) (help); Unknown parameter |Title= ignored (|title= suggested) (help); Unknown parameter |Year= ignored (|year= suggested) (help)
. ISBN 013805326X. {{cite book}}: Missing or empty |title= (help); Unknown parameter |Author= ignored (|author= suggested) (help); Unknown parameter |Publisher= ignored (|publisher= suggested) (help); Unknown parameter |Title= ignored (|title= suggested) (help); Unknown parameter |Year= ignored (|year= suggested) (help)
. ISBN 047130932X. {{cite book}}: Missing or empty |title= (help); Unknown parameter |Author= ignored (|author= suggested) (help); Unknown parameter |Publisher= ignored (|publisher= suggested) (help); Unknown parameter |Title= ignored (|title= suggested) (help); Unknown parameter |Year= ignored (|year= suggested) (help)
. ISBN 084931397X. {{cite book}}: Missing or empty |title= (help); Unknown parameter |Author= ignored (|author= suggested) (help); Unknown parameter |Publisher= ignored (|publisher= suggested) (help); Unknown parameter |Title= ignored (|title= suggested) (help); Unknown parameter |Year= ignored (|year= suggested) (help)

External links

Introduction to Electromagnetism Fu/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/index.htm MIT Video Lectures - Electricity and Magnetism] from Spring 2002. Taught by Professor Walter Lewin.
Electricity and Magnetism - an online textbook (uses algebra, with optional calculus-based sections)
Electromagnetic Field Theory - an online textbook (uses calculus)
Classical Electromagnetism: An intermediate level course - an online intermediate level texbook downloadable as PDF file

^ International Union of Pure and Applied Chemistry (1993). Quantities, Units and Symbols in Physical Chemistry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. pp. 14–15. Electronic version.

[1] International Union of Pure and Applied Chemistry (1993). Quantities, Units and Symbols in Physical Chemistry, 2nd edition, Oxford: Blackwell Science. ISBN 0-632-03583-8. pp. 14–15. Electronic version.

[1]

@@ Line 1: / Line 1: @@
-'''Electromagnetism''' is the [[physics]] of the [[electromagnetic field]]: a [[field (physics)|field]], encompassing all of [[space]], which exerts a [[force]] on those [[particle]]s that possess the property of [[electric charge]], and is in turn affected by the presence and motion of such particles. The term '''electrodynamics''' is sometimes used to refer to the combination of electromagnetism with [[mechanics]], and deals with the effects of the electromagnetic field on the dynamic behavior of electrically charged particles. Electromagnetism encompasses various real-world '''electromagnetic phenomena'''.
 == Electric and magnetic fields ==
-It is often convenient to understand the electromagnetic field in terms of two separate fields: the [[electric field]] and the [[magnetic field]]. A non-zero electric field is produced by the presence of [[electric charge|electrically charged]] particles, and gives rise to the electric [[force]]; this is the force that causes [[static electricity]] and drives the flow of electric charge ([[current (electricity)|electric current]]) in [[conductor (material)|electrical conductors]]. The magnetic field, on the other hand, can be produced by the ''motion'' of electric charges, or electric current, and gives rise to the magnetic force associated with [[magnet]]s.
+It is often convenient to understand the electromagnetic field in terms of two separate fields: the [[electric field]] and the [[magnetic field]]. A non-zero electric field is produced by the presence of [[electric charge|electrically charged]] particles, and gives rise to the electric [[ the electricity)|electric current]]) in [[conductor (material)|electrical conductors]]. The magnetic field, on the other hand, can be produced by the ''motion'' of electric charges, or electric current, and gives rise to the magnetic force associated with [[magnet]]s.
-The term "electromagnetism" comes from the fact that the electric and magnetic fields generally cannot be described independently of one another. A changing magnetic field produces an electric field (this is the phenomenon of [[electromagnetic induction]], which underlies the operation of [[electrical generator]]s, [[induction motor]]s, and [[transformer]]s). Similarly, a changing electric field generates a magnetic field.
+The term "electromagnetism" comes from the fact that the electric and magnetic fields generally cannot be described independently of one another. A changing magnetic field produces an electric field (generator]]s, [[induction motor]]s, and [[transformer]]s). Similarly, a changing electric field generates a magnetic field.
+Because field, i.e., an electromagnetic [[wave]]. Different [[ ray]]s at the highest frequencies.
-Because of this interdependence of the electric and magnetic fields, it makes sense to consider them as a single, theoretically coherent entity &mdash; the electromagnetic field. This unification, which was completed by [[James Clerk Maxwell]], is one of the triumphs of [[19th century]] physics. It had far-reaching consequences, one of which was the elucidation of the nature of [[light]]: as it turns out, what we think of as "light" is actually a propagating [[oscillation|oscillatory]] disturbance in the electromagnetic field, i.e., an electromagnetic [[wave]]. Different [[frequency|frequencies]] of oscillation give rise to the different forms of [[electromagnetic radiation]], from [[radio wave]]s at the lowest frequencies, to visible light at intermediate frequencies, to [[gamma ray]]s at the highest frequencies.
 The theoretical implications of electromagnetism led to the development of [[special relativity]] by [[Albert Einstein]] in [[1905]].
@@ Line 19: / Line 17: @@
 == Origins of electromagnetic theory ==
 {{electromagnetism}}
-The scientist [[William Gilbert]] proposed, in his ''[[De Magnete]]'' ([[1600]]), that electricity and magnetism, while both capable of causing attraction and repulsion of objects, were distinct effects.  Mariners had noticed that lightning strikes had the ability to disturb a compass needle, but the link between lightning and electricity was not confirmed until [[Benjamin Franklin|Franklin's]] proposed experiments (performed initially by others) in [[1752]].  One of the first to discover and publish a link between man-made electric current and magnetism was [[Gian Domenico Romagnosi|Romagnosi]], who in [[1802]] noticed that connecting a wire across a [[Voltaic pile]] deflected a nearby [[compass]] needle. However, the effect did not become widely known until [[1820]], when [[Hans Christian Ørsted|Ørsted]] performed a similar experiment. Ørsted's work influenced [[André-Marie Ampère|Ampère]] to produce a theory of electromagnetism that set the subject on a mathematical foundation.
+The scientist [[William Gilbert]] proposed, in his ''[[De Magnete]]'' ([[1600]]), that  the first to discover and publish a link between man-made electric current and magnetism was [[Gian Domenico Romagnosi|Romagnosi]], who in [[1802]] noticed that connecting a wire across a [[Voltaic pile]] deflected a nearby [[compass]] needle. However, the effect did not become widely known until [[1820]], when [[Hans Christian Ørsted|Ørsted]] performed a similar experiment. Ørsted's work influenced [[André-Marie Ampère|Ampère]] to produce a theory of electromagnetism that set the subject on a mathematical foundation.
 An accurate theory of electromagnetism, known as [[classical electromagnetism]], was developed by various [[physicist]]s over the course of the [[19th century]], culminating in the work of [[James Clerk Maxwell]], who unified the preceding developments into a single theory and discovered the electromagnetic nature of light. In classical electromagnetism, the electromagnetic field obeys a set of equations known as [[Maxwell's equations]], and the electromagnetic force is given by the [[Lorentz force|Lorentz force law]].
-One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with [[classical mechanics]], but it is compatible with [[special relativity]]. According to Maxwell's equations, the [[speed of light]] is a universal constant, dependent only on the [[Permittivity|electrical permittivity]] and [[magnetic permeability]] of the [[vacuum]]. This violates [[Galilean invariance]], a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a [[luminiferous aether]] through which the light propagates. However, subsequent experiments efforts failed to detect the presence of the aether. In [[1905]], [[Albert Einstein]] solved the problem with the introduction of [[special relativity]], which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism.
+One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with [[classical mechanics]], but it is compatible with [[special relativity]]. According to Maxwell's equations, the [[speed of light]] is a universal constant, dependent only on the [[Permittivity|electrical permittivity]] and [[magnetic permeability]] of the [[vacuum]]. This violates [[Galilean invariance]], a long-standing cornerstone of classical mechanics. One way to reconcile the two theories is to assume the existence of a [[luminiferous aether]] through which the . In [[1905]], [[Albert Einstein]] solved the problem with the introduction of [[special relativity]], which replaces classical kinematics with a new theory of kinematics that is compatible with classical electromagnetism.
 In addition, Relativity theory shows that in moving frames of reference a magnetic field becomes an electrostatic field and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term '''Electromagnetism'''.
@@ Line 29: / Line 27: @@
 ==Failures of classical electromagnetism==
-In another paper published in that same year, Einstein undermined the very foundations of classical electromagnetism. His theory of the [[photoelectric effect]] (for which he won the Nobel prize for physics) posited that light could exist in discrete particle-like quantities, which later came to be known as [[photon]]s. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the [[ultraviolet catastrophe]] presented by [[Max Planck]] in [[1900]]. In his work, Planck showed that hot objects emit [[electromagnetic radiation]] in discrete packets, which leads to a finite total [[energy]] emitted as [[black body radiation]]. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of [[quantum mechanics]], which, when formulated in [[1925]], necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the [[1940s]], is known as [[quantum electrodynamics]] (or "QED"), and is one of the most accurate theories known to physics.
+In another paper published in that same year, Einstein undermined the very foundations of classical electromagnetism. His theory of the [[photoelectric effect]] (for which he won the Nobel prize for phcs) posited that light could exist in discrete particle-like quantities, which later came to be known as [[photon]]s. Einstein's theory of the photoelectric effect extended the insights that appeared in the solution of the [[ultraviolet catastrophe]] presented by [[Max Planck]] in [[1900]]. In his work, Planck showed that hot objects emit [[electromagnetic radiation]] in discrete packets, which leads to a finite total [[energy]] emitted as [[black body radiation]]. Both of these results were in direct contradiction with the classical view of light as a continuous wave. Planck's and Einstein's theories were progenitors of [[quantum mechanics]], which, when formulated in [[1925]], necessitated the invention of a quantum theory of electromagnetism. This theory, completed in the [[1940s]], is known as [[quantum electrodynamics]] (or "QED"), and is one of the most accurate theories known to physics.
 ==SI electricity units==
@@ Line 44: / Line 42: @@
 == External links ==
-* [http://www.rmcybernetics.com/science/physics/electromagnetism_intro_electric_force.htm Introduction to Electromagnetism] From the basics to advanced level science
+* [http://www.rmcybernetics.com/science/physics/electromagnetism_intro_electric_force.htm Introduction to Electromagnetism] Fu/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/index.htm MIT Video Lectures - Electricity and Magnetism] from Spring 2002. Taught by Professor Walter Lewin.
-*[http://ocw.mit.edu/OcwWeb/Physics/8-02Electricity-and-MagnetismSpring2002/VideoLectures/index.htm MIT Video Lectures - Electricity and Magnetism] from Spring 2002. Taught by Professor Walter Lewin.
 * [http://www.lightandmatter.com/area1book4.html Electricity and Magnetism] - an online textbook (uses algebra, with optional calculus-based sections)
 * [http://www.plasma.uu.se/CED/Book/ Electromagnetic Field Theory] - an online textbook (uses calculus)

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