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Electromagnetism
Electricity · Magnetism
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Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. The electromagnetic field is a physical field produced by electrically charged objects. In Physics, a field is a Physical quantity associated to each point of Spacetime. In Physics, a force is whatever can cause an object with Mass to Accelerate. In Particle physics, an elementary particle or fundamental particle is a particle not known to have substructure that is it is not known to be made Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers). In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can Faraday's law of induction describes an important basic law of electromagnetism which is involved in the working of Transformers Inductors and many forms of In Electricity generation, an electrical generator is a device that converts Mechanical energy to Electrical energy, generally using Electromagnetic An induction motor (IM is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors Similarly, a changing electric field generates a magnetic field. Because of this interdependence of the electric and magnetic fields, it makes sense to consider them as a single coherent entity - the electromagnetic field.

The magnetic field is produced by the motion of electric charges, i. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. e. , electric current. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. The magnetic field causes the magnetic force associated with magnets. A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field.

The theoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical

Contents

History

While preparing for an evening lecture on 21 April 1820, Hans Christian Ørsted developed an experiment which provided evidence that surprised him. As he was setting up his materials, he noticed a compass needle deflected from magnetic north when the electric current from the battery he was using was switched on and off. This deflection convinced him that magnetic fields radiate from all sides of a wire carrying an electric current, just as light and heat do, and that it confirmed a direct relationship between electricity and magnetism.

At the time of discovery, Ørsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework. However, three months later he began more intensive investigations. Soon thereafter he published his findings, proving that an electric current produces a magnetic field as it flows through a wire. The CGS unit of magnetic induction (oersted) is named in honor of his contributions to the field of electromagnetism.

His findings resulted in intensive research throughout the scientific community in electrodynamics. Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently They influenced French physicist André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers Ørsted's discovery also represented a major step toward a unified concept of energy.

Ørsted was not the first person to examine the relation between electricity and magnetism. In 1802 Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle by electrostatic charges. Gian Domenico Romagnosi ( December 11, 1761 &ndash June 8, 1835) was an Italian Philosopher, Economist and He interpreted his observations as The Relation between electricity and magnetism. Actually, no galvanic current existed in the setup and hence no electromagnetism was present. An account of the discovery was published in 1802 in an Italian newspaper, but it was largely overlooked by the contemporary scientific community.

This unification, which was observed by Michael Faraday, extended by James Clerk Maxwell, and partially reformulated by Oliver Heaviside and Heinrich Hertz, is one of the triumphs of 19th century physics. Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. Heinrich Rudolf Hertz ( February 22, 1857 – January 1, 1894) was a German physicist who clarified and expanded the electromagnetic theory It had far-reaching consequences, one of which was the understanding of the nature of light. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 As it turns out, what is thought of as "light" is actually a propagating oscillatory disturbance in the electromagnetic field, i. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states e. , an electromagnetic wave. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. Different frequencies of oscillation give rise to the different forms of electromagnetic radiation, from radio waves at the lowest frequencies, to visible light at intermediate frequencies, to gamma rays at the highest frequencies. Frequency is a measure of the number of occurrences of a repeating event per unit Time. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions

The electromagnetic force

Main article: Electromagnetic force

The force that the electromagnetic field exerts on electrically charged particles, called the electromagnetic force, is one of the four fundamental forces. In Physics, the electromagnetic force is the force that the Electromagnetic field exerts on electrically charged particles In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms 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. In particle physics the strong interaction, or strong force, or color force, holds Quarks and Gluons together to form Protons and The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Gravitation is a natural Phenomenon by which objects with Mass attract one another All other forces are ultimately derived from these fundamental forces.

The electromagnetic force is the one responsible for practically all the phenomena encountered in daily life, with the exception of gravity. 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. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J 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. In Physics, Chemistry, and Biology, intermolecular forces are forces that act between stable Molecules or between functional groups of In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by It also includes all forms of chemical phenomena, which arise from interactions between electron orbitals. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties In Chemistry, a molecular orbital (or MO) is a region in which an Electron may be found in a Molecule.

Classical electrodynamics

Main article: Classical electrodynamics

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. Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently William Gilbert, also known as Gilbard ( Colchester, England, May 24, 1544 &ndash London, England, November 30 De Magnete Magneticisque Corporibus et de Magno Magnete Tellure ( On the Magnet and Magnetic Bodies and on That Great Magnet the Earth) is a scientific 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's proposed experiments in 1752. Benjamin Franklin ( April 17 1790 was one of the Founding Fathers of the United States of America. One of 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. Gian Domenico Romagnosi ( December 11, 1761 &ndash June 8, 1835) was an Italian Philosopher, Economist and A voltaic pile is a set of individual Voltaic cells placed in series A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists 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. André-Marie Ampère (20 January 1775 &ndash 10 June 1836 was a French Physicist and Mathematician who is generally credited as one of the main discoverers

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. Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently A physicist is a Scientist who studies or practices Physics. Physicists study a wide range of physical phenomena in many branches of physics spanning James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. 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. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric In Physics, the Lorentz force is the Force on a Point charge due to Electromagnetic fields It is given by the following equation

One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with classical mechanics, but it is compatible with special relativity. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial According to Maxwell's equations, the speed of light in a vacuum is a universal constant, dependent only on the electrical permittivity and magnetic permeability of free space. Permittivity is a Physical quantity that describes how an Electric field affects and is affected by a Dielectric medium and is determined by the ability In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. This violates Galilean invariance, a long-standing cornerstone of classical mechanics. Galilean invariance or Galilean relativity is a Principle of relativity which states that the fundamental laws of physics are the same in all Inertial One way to reconcile the two theories is to assume the existence of a luminiferous aether through which the light propagates. In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation However, subsequent experimental efforts failed to detect the presence of the aether. After important contributions of Hendrik Lorentz and Henri Poincaré, 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. Hendrik Antoon Lorentz ( July 18, 1853 &ndash February 4, 1928) was a Dutch Physicist who shared the 1902 Nobel Jules Henri Poincaré ( 29 April 1854 &ndash 17 July 1912) (ˈʒyl ɑ̃ˈʁi pwɛ̃kaˈʁe was a French Mathematician Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial (For more information, see History of special relativity. The History of special relativity consists of many theoretical and empirical results of physicists like Hendrik Lorentz and Henri Poincaré, which culminated in the )

In addition, relativity theory shows that in moving frames of reference a magnetic field transforms to a field with a nonzero electric component and vice versa; thus firmly showing that they are two sides of the same coin, and thus the term "electromagnetism". (For more information, see Classical electromagnetism and special relativity. The theory of Special relativity plays an important role in the modern theory of Classical electromagnetism. )

The photoelectric effect

Main article: Photoelectric effect

In another paper published in that same year, Albert Einstein undermined the very foundations of classical electromagnetism. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons 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 photons. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena 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. The ultraviolet catastrophe, also called the Rayleigh-Jeans catastrophe was a prediction of early 20th century Classical physics that an ideal Black body at 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. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός The Electromagnetic radiation emitted by a Black body. You may also be looking for Incandescence, the radiation from a body 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. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons This theory, completed in the 1940s, is known as quantum electrodynamics (or "QED"), and is one of the most accurate theories known to physics. Quantum electrodynamics ( QED) is a relativistic Quantum field theory of Electrodynamics.

Definition

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. Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently Mechanics ( Greek) is the branch of Physics concerned with the behaviour of physical bodies when subjected to Forces or displacements

Units

Electromagnetic units are part of a system of electrical units based primarily upon the magnetic properties of electric currents, the fundamental cgs unit being the ampere. The units are:

In the electromagnetic cgs system, electrical current is a fundamental quantity defined via Ampère's law and takes the permeability as a dimensionless quantity (relative permeability) whose value in a vacuum is unity. The ampere, in practice often shortened to amp, (symbol A is a unit of Electric current, or amount of Electric charge per second The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. This is about the capacitance unit of measure For the charge unit see Faraday (unit. The henry (symbol H is the SI unit of Inductance. It is named after Joseph Henry (1797-1878 the American scientist who discovered electromagnetic The ohm (symbol Ω) is the SI unit of Electrical impedance or in the Direct current case Electrical resistance, The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. In Electromagnetism, permeability is the degree of Magnetization of a material that responds linearly to an applied Magnetic field. As a consequence, the square of the speed of light appears explicitly in some of the equations interrelating quantities in this system.

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SI electromagnetism units
Symbol Name of Quantity Derived Units Unit Base Units
I Electric current ampere (SI base unit) A A (= W/V = C/s)
q Electric charge, Quantity of electricity coulomb C A·s
V Potential difference or Electromotive force volt V J/C = kg·m2·s−3·A−1
R, Z, X 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 Power, Electrical watt W V·A = kg·m2·s−3
C Capacitance farad F C/V = kg−1·m−2·A2·s4
Elastance reciprocal farad F−1 V/C = kg·m2·A−2·s−4
E Electric field 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
χe Electric susceptibility (dimensionless) - -
G, Y, B Conductance, Admittance, Susceptance siemens S Ω−1 = kg−1·m−2·s3·A2
σ Conductivity siemens per metre S/m kg−1·m−3·s3·A2
B Magnetic field (Magnetic flux density) tesla T Wb/m2 = kg·s−2·A−1 = N·A−1·m−1
Φm Magnetic flux weber Wb V·s = kg·m2·s−2·A−1
H Magnetizing field ampere per metre A/m A·m−1
Reluctance ampere-turn per weber A/Wb kg−1·m−2·s2·A2
L 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
χm Magnetic susceptibility (dimensionless) - -

See also

References

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External links

Dictionary

electromagnetism

-noun

  1. A unified fundamental force that combines the aspects of electricity and magnetism and is one of the four fundamental forces. (technically it can be unified with weak nuclear to form electroweak) Its gauge boson is the photon.
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