Electromagnetism
Articles about |
Electromagnetism |
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In physics, electromagnetism is an interaction that occurs between
The electromagnetic force is responsible for many of the
Electromagnetism has been studied since ancient times. Many ancient civilizations, including the
In the modern era, scientists have continued to refine the theorem of electromagnetism to take into account the effects of
History
Ancient world
Investigation into electromagnetic phenomena began about 5,000 years ago. There is evidence that the ancient
19th century
Electricity and magnetism were originally considered to be two separate forces. This view changed with the publication of James Clerk Maxwell's 1873 A Treatise on Electricity and Magnetism[5] in which the interactions of positive and negative charges were shown to be mediated by one force. There are four main effects resulting from these interactions, all of which have been clearly demonstrated by experiments:
- Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel.[6]
- Magnetic poles (or states of polarization at individual points) attract or repel one another in a manner similar to positive and negative charges and always exist as pairs: every north pole is yoked to a south pole.[7]
- An electric current inside a wire creates a corresponding circumferential magnetic field outside the wire. Its direction (clockwise or counter-clockwise) depends on the direction of the current in the wire.[8]
- A current is induced in a loop of wire when it is moved toward or away from a magnetic field, or a magnet is moved towards or away from it; the direction of current depends on that of the movement.[8]
In April 1820,
His findings resulted in intensive research throughout the scientific community in electrodynamics. They influenced French physicist André-Marie Ampère's developments of a single mathematical form to represent the magnetic forces between current-carrying conductors. Ørsted's discovery also represented a major step toward a unified concept of energy.
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 key accomplishments of 19th-century mathematical physics.[12] It has had far-reaching consequences, one of which was the understanding of the nature of light. Unlike what was proposed by the electromagnetic theory of that time, light and other electromagnetic waves are at present seen as taking the form of quantized, self-propagating oscillatory electromagnetic field disturbances called photons. 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.
Ørsted was not the only person to examine the relationship between electricity and magnetism. In 1802, Gian Domenico Romagnosi, an Italian legal scholar, deflected a magnetic needle using a Voltaic pile. The factual setup of the experiment is not completely clear, nor if current flowed across the needle or not. An account of the discovery was published in 1802 in an Italian newspaper, but it was largely overlooked by the contemporary scientific community, because Romagnosi seemingly did not belong to this community.[13]
An earlier (1735), and often neglected, connection between electricity and magnetism was reported by a Dr. Cookson.[14] The account stated:
A tradesman at Wakefield in Yorkshire, having put up a great number of knives and forks in a large box ... and having placed the box in the corner of a large room, there happened a sudden storm of thunder, lightning, &c. ... The owner emptying the box on a counter where some nails lay, the persons who took up the knives, that lay on the nails, observed that the knives took up the nails. On this the whole number was tried, and found to do the same, and that, to such a degree as to take up large nails, packing needles, and other iron things of considerable weight ...
E. T. Whittaker suggested in 1910 that this particular event was responsible for lightning to be "credited with the power of magnetizing steel; and it was doubtless this which led Franklin in 1751 to attempt to magnetize a sewing-needle by means of the discharge of Leyden jars."[15]
A fundamental force
The electromagnetic force is the second strongest of the four known
Roughly speaking, all the forces involved in interactions between atoms can be explained by the electromagnetic force acting between the electrically charged atomic nuclei and electrons of the atoms. Electromagnetic forces also explain how these particles carry momentum by their movement. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which result from the intermolecular forces that act between the individual molecules in our bodies and those in the objects. The electromagnetic force is also involved in all forms of chemical phenomena.
A necessary part of understanding the intra-atomic and intermolecular forces is the effective force generated by the momentum of the electrons' movement, such that as electrons move between interacting atoms they carry momentum with them. As a collection of electrons becomes more confined, their minimum momentum necessarily increases due to the Pauli exclusion principle. The behaviour of matter at the molecular scale including its density is determined by the balance between the electromagnetic force and the force generated by the exchange of momentum carried by the electrons themselves.[19]
Classical electrodynamics
In 1600,
One of the first to discover and publish a link between human-made electric current and magnetism was
A theory of electromagnetism, known as classical electromagnetism, was developed by several physicists during the period between 1820 and 1873, when James Clerk Maxwell's treatise was published, which unified previous developments into a single theory, proposing that light was an electromagnetic wave propagating in the luminiferous ether.[25] In classical electromagnetism, the behavior of the electromagnetic field is described by a set of equations known as Maxwell's equations, and the electromagnetic force is given by the Lorentz force law.[26]
One of the peculiarities of classical electromagnetism is that it is difficult to reconcile with
In addition, relativity theory implies that in moving frames of reference, a magnetic field transforms to a field with a nonzero electric component and conversely, a moving electric field transforms to a nonzero magnetic component, thus firmly showing that the phenomena are two sides of the same coin. Hence the term "electromagnetism". (For more information, see Classical electromagnetism and special relativity and Covariant formulation of classical electromagnetism.)
Today few problems in electromagnetism remain unsolved. These include: the lack of
Extension to nonlinear phenomena
The Maxwell equations are linear, in that a change in the sources (the charges and currents) results in a proportional change of the fields. Nonlinear dynamics can occur when electromagnetic fields couple to matter that follows nonlinear dynamical laws.[27] This is studied, for example, in the subject of magnetohydrodynamics, which combines Maxwell theory with the Navier–Stokes equations.[28] Another branch of electromagnetism dealing with nonlinearity is nonlinear optics.
Quantities and units
Here is a list of common units related to electromagnetism:[29]
In the electromagnetic
Symbol[31] | 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, ΔV; Δϕ; E, ξ | potential difference; voltage; electromotive force
|
volt | V = J/C | kg⋅m2⋅s−3⋅A−1 |
R; Z; X | 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 |
ΦE | 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 |
χe | 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, ΦM, ΦB | 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
|
square meter
|
A⋅m2 = J⋅T−1 | A⋅m2 |
σ | mass magnetization | square meter per kilogram
|
A⋅m2/kg | A⋅m2⋅kg−1 |
Formulas for physical laws of electromagnetism (such as
Applications
The study of electromagnetism informs electric circuits, magnetic circuits, and semiconductor devices' construction.
See also
- Abraham–Lorentz force
- Aeromagnetic surveys
- Computational electromagnetics
- Double-slit experiment
- Electrodynamic droplet deformation
- Electromagnet
- Electromagnetic induction
- Electromagnetic wave equation
- Electromagnetic scattering
- Electromechanics
- Geophysics
- Introduction to electromagnetism
- Magnetostatics
- Magnetoquasistatic field
- Optics
- Relativistic electromagnetism
- Wheeler–Feynman absorber theory
References
- ^ Meyer, Herbert (1972). A History of Electricity and Magnetism. p. 2.
- ^ Magazine, Smithsonian; Learn, Joshua Rapp. "Mesoamerican Sculptures Reveal Early Knowledge of Magnetism". Smithsonian Magazine. Retrieved 2022-12-07.
- ISBN 978-0-387-23062-7, retrieved 2022-12-07
- ^ Meyer, Herbert (1972). A History of Electricity and Magnetism. pp. 3–4.
- S2CID 10178476.
- ^ "Why Do Like Charges Repel And Opposite Charges Attract?". Science ABC. 2019-02-06. Retrieved 2022-08-22.
- ^ "What Makes Magnets Repel?". Sciencing. Retrieved 2022-08-22.
- ^ a b Jim Lucas Contributions from Ashley Hamer (2022-02-18). "What Is Faraday's Law of Induction?". livescience.com. Retrieved 2022-08-22.
- ISSN 0036-8733.
- OCLC 1261807533.)
{{cite book}}
: CS1 maint: others (link - OCLC 40499222.
- ISBN 0198505949.
- ^ Martins, Roberto de Andrade. "Romagnosi and Volta's Pile: Early Difficulties in the Interpretation of Voltaic Electricity" (PDF). In Fabio Bevilacqua; Lucio Fregonese (eds.). Nuova Voltiana: Studies on Volta and his Times. Vol. 3. Università degli Studi di Pavia. pp. 81–102. Archived from the original (PDF) on 2013-05-30. Retrieved 2010-12-02.
- ^ VIII. An account of an extraordinary effect of lightning in communicating magnetism. Communicated by Pierce Dod, M.D. F.R.S. from Dr. Cookson of Wakefield in Yorkshire. Phil. Trans. 1735 39, 74-75, published 1 January 1735
- ^ Whittaker, E.T. (1910). A History of the Theories of Aether and Electricity from the Age of Descartes to the Close of the Nineteenth Century. Longmans, Green and Company.
- ^ Rehm, Jeremy; published, Ben Biggs (2021-12-23). "The four fundamental forces of nature". Space.com. Retrieved 2022-08-22.
- ^ Browne, "Physics for Engineering and Science", p. 160: "Gravity is one of the fundamental forces of nature. The other forces such as friction, tension, and the normal force are derived from the electric force, another of the fundamental forces. Gravity is a rather weak force... The electric force between two protons is much stronger than the gravitational force between them."
- .
- ^ Purcell, "Electricity and Magnetism, 3rd Edition", p. 546: Ch 11 Section 6, "Electron Spin and Magnetic Moment."
- ISSN 0096-3941.
- ^ "Lightning! | Museum of Science, Boston".
- OCLC 51763922.
- ^ Stern, Dr. David P.; Peredo, Mauricio (2001-11-25). "Magnetic Fields – History". NASA Goddard Space Flight Center. Retrieved 2009-11-27.
- ^ "Andre-Marie Ampère". ETHW. 2016-01-13. Retrieved 2022-08-22.
- ^ Purcell, p. 436. Chapter 9.3, "Maxwell's description of the electromagnetic field was essentially complete."
- ^ Purcell: p. 278: Chapter 6.1, "Definition of the Magnetic Field." Lorentz force and force equation.
- S2CID 219451710.
- .
- ^ "Essentials of the SI: Base & derived units". physics.nist.gov. Retrieved 2022-08-22.
- ISSN 1476-4687.
- ISBN 0-632-03583-8. pp. 14–15. Electronic version.
- ^ "Conversion of formulae and quantities between unit systems" (PDF). www.stanford.edu. Archived from the original (PDF) on 5 October 2022. Retrieved 29 January 2022.
Further reading
Web sources
- Nave, R. "Electricity and magnetism". HyperPhysics. Georgia State University. Retrieved 2013-11-12.
- Khutoryansky, E. "Electromagnetism – Maxwell's Laws". YouTube. Retrieved 2014-12-28.
Textbooks
- G.A.G. Bennet (1974). Electricity and Modern Physics (2nd ed.). Edward Arnold (UK). ISBN 978-0-7131-2459-0.
- Browne, Michael (2008). Physics for Engineering and Science (2nd ed.). McGraw-Hill/Schaum. ISBN 978-0-07-161399-6.
- Dibner, Bern (2012). Oersted and the discovery of electromagnetism. Literary Licensing, LLC. ISBN 978-1-258-33555-7.
- Durney, Carl H.; Johnson, Curtis C. (1969). Introduction to modern electromagnetics. McGraw-Hill. ISBN 978-0-07-018388-9.
- Feynman, Richard P. (1970). The Feynman Lectures on Physics Vol II. Addison Wesley Longman. ISBN 978-0-201-02115-8.
- Fleisch, Daniel (2008). A Student's Guide to Maxwell's Equations. Cambridge, UK: Cambridge University Press. ISBN 978-0-521-70147-1.
- I.S. Grant; W.R. Phillips; Manchester Physics (2008). Electromagnetism (2nd ed.). John Wiley & Sons. ISBN 978-0-471-92712-9.
- ISBN 978-0-13-805326-0.
- ISBN 978-0-471-30932-1.
- Moliton, André (2007). Basic electromagnetism and materials. New York: Springer-Verlag New York. ISBN 978-0-387-30284-3.
- ISBN 978-0-07-004908-6.
- Purcell, Edward M and Morin, David. (2013). Electricity and Magnetism, 820p (3rd ed.). Cambridge University Press, New York. ISBN 978-1-107-01402-2.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - Rao, Nannapaneni N. (1994). Elements of engineering electromagnetics (4th ed.). Prentice Hall. ISBN 978-0-13-948746-0.
- Rothwell, Edward J.; Cloud, Michael J. (2001). Electromagnetics. CRC Press. ISBN 978-0-8493-1397-4.
- Tipler, Paul (1998). Physics for Scientists and Engineers: Vol. 2: Light, Electricity and Magnetism (4th ed.). W.H. Freeman. ISBN 978-1-57259-492-0.
- Wangsness, Roald K.; Cloud, Michael J. (1986). Electromagnetic Fields (2nd ed.). Wiley. ISBN 978-0-471-81186-2.
General coverage
- A. Beiser (1987). Concepts of Modern Physics (4th ed.). McGraw-Hill (International). ISBN 978-0-07-100144-1.
- L.H. Greenberg (1978). Physics with Modern Applications. Holt-Saunders International W.B. Saunders and Co. ISBN 978-0-7216-4247-5.
- ISBN 978-0-07-025734-4.
- J.B. Marion; W.F. Hornyak (1984). Principles of Physics. Holt-Saunders International Saunders College. ISBN 978-4-8337-0195-2.
- H.J. Pain (1983). The Physics of Vibrations and Waves (3rd ed.). John Wiley & Sons. ISBN 978-0-471-90182-2.
- C.B. Parker (1994). McGraw Hill Encyclopaedia of Physics (2nd ed.). McGraw Hill. ISBN 978-0-07-051400-3.
- R. Penrose (2007). ISBN 978-0-679-77631-4.
- P.A. Tipler; G. Mosca (2008). Physics for Scientists and Engineers: With Modern Physics (6th ed.). W.H. Freeman and Co. ISBN 978-1-4292-0265-7.
- P.M. Whelan; M.J. Hodgeson (1978). Essential Principles of Physics (2nd ed.). John Murray. ISBN 978-0-7195-3382-2.
External links
- Magnetic Field Strength Converter
- Electromagnetic Force – from Eric Weisstein's World of Physics