Editing Electromagnetic radiation (section)

=== Properties ===

Electromagnetic radiation is produced by accelerating charged particles and can be naturally emitted,<ref name="Cloude">{{cite book |last1=Cloude |first1=Shane |url=https://books.google.com/books?id=8-NLj54dU2YC&q=%22electromagnetic+radiation%22+charges+accelerates&pg=PA28 |title=An Introduction to Electromagnetic Wave Propagation and Antennas |date=1995 |publisher=Springer Science and Business Media |isbn=978-0-387-91501-2 |pages=28–33}}</ref><ref name="Bettini">{{cite book |last1=Bettini |first1=Alessandro |url=https://books.google.com/books?id=Ip9xDQAAQBAJ&q=%22electromagnetic+waves%22+charges+accelerating&pg=PA95 |title=A Course in Classical Physics, Vol. 4 – Waves and Light |date=2016 |publisher=Springer |isbn=978-3-319-48329-0 |pages=95, 103}}</ref> as from the Sun and other celestial bodies, or artificially generated for various applications. The energy in electromagnetic waves is sometimes called [[radiant energy]].<ref>{{Cite news |title=What Is Electromagnetic Radiation? |url=https://www.livescience.com/38169-electromagnetism.html |url-status=live |archive-url=https://web.archive.org/web/20170904152301/https://www.livescience.com/38169-electromagnetism.html |archive-date=4 September 2017 |access-date=4 September 2017 |work=Live Science}}</ref><ref>{{Cite book |url={{google books |plainurl=y |id=AUriAAAAMAAJ|page=22}} |title=The Michigan Technic |date=1960 |publisher=UM Libraries |language=en}}</ref> The electromagnetic waves' energy does not need a propagating medium to travel through space; they move through a vacuum at the speed of light.<ref>{{Cite web |date=2016-08-10 |title=Anatomy of an Electromagnetic Wave |url=https://science.nasa.gov/ems/02_anatomy/ |access-date=2025-03-25 |website=NASA Science |language=en-US}}</ref>
[[File:Electromagneticwave3D.gif|thumb|Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. The electric and magnetic fields in such a wave are in phase with each other, reaching minima and maxima together.]]

Electric and magnetic fields obey the properties of [[superposition principle|superposition]]. Thus, a field due to any particular particle or time-varying electric or magnetic field contributes to the fields present in the same space due to other causes. Further, as they are [[Vector (geometric)|vector]] fields, all magnetic and electric field vectors add together according to [[vector addition]].<ref>Purcell, p442: "Any number of electromagnetic waves can propagate through the same region without affecting one another. The field '''E''' at a space time point is the vector sum of the electric fields of the individual waves, and the same goes for '''B'''".</ref> For example, in optics two or more coherent light waves may interact and by constructive or destructive [[Interference (wave propagation)|interference]] yield a resultant irradiance deviating from the sum of the component irradiances of the individual light waves.<ref>{{Cite web|title=PV Performance Modeling Collaborative {{!}} Plane of Array (POA) Irradiance|url=https://pvpmc.sandia.gov/modeling-steps/1-weather-design-inputs/plane-of-array-poa-irradiance/|access-date=14 January 2022|language=en-US|archive-date=14 January 2022|archive-url=https://web.archive.org/web/20220114171617/https://pvpmc.sandia.gov/modeling-steps/1-weather-design-inputs/plane-of-array-poa-irradiance/|url-status=live}}</ref> The electromagnetic fields of light are not affected by traveling through static electric or magnetic fields in a linear medium such as a vacuum. However, in nonlinear media, such as some [[crystal]]s, interactions can occur between light and static electric and magnetic fields—these interactions include the [[Faraday effect]] and the [[Kerr effect]].<ref>{{cite journal|title=Experimental observation of relativistic nonlinear Thomson scattering|first1=Szu-yuan|last1=Chen|first2=Anatoly|last2=Maksimchuk|first3=Donald|last3=Umstadter|date=17 December 1998|journal=Nature|volume=396|issue=6712|pages=653–655|doi=10.1038/25303|arxiv=physics/9810036|bibcode=1998Natur.396..653C|s2cid=16080209}}</ref><ref name="crowther-1920">{{Cite book |last=Crowther |first=James Arnold |author-link=James Arnold Crowther |url={{google books|plainurl=y|id=iWe4AAAAIAAJ|page=5}} |title=The life and discoveries of Michael Faraday |date=1920 |publisher=Society for promoting Christian knowledge |pages=54–57 |access-date=15 June 2014}}</ref>

In [[refraction]], a wave crossing from one medium to another of different [[density]] alters its [[Velocity|speed and direction]] upon entering the new medium. The ratio of the refractive indices of the media determines the degree of refraction, and is summarized by [[Snell's law]]. Light of composite wavelengths (natural sunlight) disperses into a visible [[electromagnetic spectrum|spectrum]] passing through a prism, because of the wavelength-dependent [[refractive index]] of the [[Prism (optics)|prism]] material ([[Dispersion (optics)|dispersion]]); that is, each component wave within the composite light is bent a different amount.<ref>{{Cite journal|title=Prisms|url=https://www.spectroscopyonline.com/view/prisms|access-date=17 January 2021|journal=Spectroscopy|series=Spectroscopy-09-01-2008|date=September 2008|volume=23|issue=9|archive-date=22 January 2021|archive-url=https://web.archive.org/web/20210122044456/https://www.spectroscopyonline.com/view/prisms|url-status=live}}</ref>

EM radiation exhibits both wave properties and [[Subatomic particle|particle]] properties at the same time (known as [[wave–particle duality]]). Both wave and particle characteristics have been confirmed in many experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances. For example, when electromagnetic radiation is absorbed by matter, particle-like properties will be more obvious when the average number of photons in the cube of the relevant wavelength is much smaller than 1. It is not so difficult to experimentally observe non-uniform deposition of energy when light is absorbed, however this alone is not evidence of "particulate" behavior. Rather, it reflects the quantum nature of ''matter''.<ref>{{cite web |url=http://www.qo.phy.auckland.ac.nz/talks/photoelectric.pdf|archive-url=https://web.archive.org/web/20070627171942/http://www.qo.phy.auckland.ac.nz/talks/photoelectric.pdf|url-status=dead|archive-date=27 June 2007|title=Einstein and the Photoelectric Effect |first=H. J. |last=Carmichael |publisher=Quantum Optics Theory Group, University of Auckland |access-date=22 December 2009}}</ref> A [[Quantum mechanics|quantum theory]] of the interaction between electromagnetic radiation and matter such as electrons is described by the theory of [[quantum electrodynamics]].

Electromagnetic waves can be [[Polarization (waves)|polarized]], reflected, refracted, or [[diffracted]], and can interfere with each other.<ref>{{Cite web |title=DATE |url=http://galileo.phys.virginia.edu/classes/usem/SciImg/home_files/introduction.htm |url-status=live |archive-url=https://web.archive.org/web/20150512060344/http://galileo.phys.virginia.edu/classes/usem/SciImg/home_files/introduction.htm |archive-date=12 May 2015 |access-date=4 September 2017 |website=galileo.phys.virginia.edu}}</ref><ref>{{Cite web |title=Physics – Waves |url=http://www-jcsu.jesus.cam.ac.uk/~rpc25/notes/physics/waves/waves.html |url-status=live |archive-url=https://web.archive.org/web/20170904153721/http://www-jcsu.jesus.cam.ac.uk/~rpc25/notes/physics/waves/waves.html |archive-date=4 September 2017 |access-date=4 September 2017 |website=www-jcsu.jesus.cam.ac.uk}}</ref><ref>{{Cite web |title=Wave Behaviors {{!}} Science Mission Directorate |url=https://science.nasa.gov/ems/03_behaviors |url-status=live |archive-url=https://web.archive.org/web/20170514053337/https://science.nasa.gov/ems/03_behaviors |archive-date=14 May 2017 |access-date=4 September 2017 |website=science.nasa.gov |date=10 August 2016 |language=en}}</ref> Some experiments display both the wave and particle natures of electromagnetic waves, such as the self-interference of a single [[photon]].<ref>{{cite journal|doi=10.1119/1.1737397|url=http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf|title=Observing the quantum behavior of light in an undergraduate laboratory|year=2004|last1=Thorn|first1=J. J.|last2=Neel|first2=M. S.|last3=Donato|first3=V. W.|last4=Bergreen|first4=G. S.|last5=Davies|first5=R. E.|last6=Beck|first6=M.|journal=American Journal of Physics|volume=72|issue=9|pages=1210|bibcode=2004AmJPh..72.1210T|url-status=live|archive-url=https://web.archive.org/web/20160201214040/http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf|archive-date=1 February 2016}}</ref> When a low intensity light is sent through an [[interferometer]] it will detected by a [[photomultiplier]] or other sensitive detector only along one arm of the device, consistent with particle properties, and yet the accumulated effect of many such detections will be interference consistent with wave properties.