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magnetism [2019/06/03 18:29]
magnetism [2020/12/07 00:10] (current)
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 +====== Magnetism ======
  
 +|< 100% >|
 +| //[[user/Stan Zurek]], Magnetism, [[http://Encyclopedia-Magnetica.com|Encyclopedia-Magnetica.com]], {accessed on @YEAR@-@MONTH@-@DAY@}// |
 +
 +
 +**Magnetism** - a physical phenomenon associated with [[magnetic field]], generated by [[electric current]], motion of [[electric charge|electric charges]],  properties of elementary particles (e.g. electron [[spin]]), or combination of all of these factors. [([[http://www.britannica.com/EBchecked/topic/357334/magnetism|Magnetism, Encyclopaedia Britannica, {accessed 3 Nov 2012}]])] [([[http://books.google.com/books?isbn=9781438110134|Joe Rosen, Encyclopedia of Physics, Infobase Publishing, 2009, ISBN 9781438110134, p. 197]])]
 +
 +<box 25% left #f0f0f0>
 +[[Horseshoe magnet]] is a popular symbol of magnetism
 +[[/file/horseshoe_magnet_magnetica.jpg|{{/horseshoe_magnet_magnetica.jpg}}]]
 +{{page>insert/by_SZ}}
 +</box>
 +
 +The term **[[electromagnetism]]** refers to mutual relationship between [[magnetic field]] and [[electric field]], which can be mathematically described with [[Maxwell equations|Maxwell's equations]].
 +
 +Depending on the context, the term **magnetism** is also sometimes used to differentiate [[magnetostatic]] (non-changing) fields from electromagnetic (varying), whereas in a wider context **magnetism** includes all magnetic phenomena (magnetostatic or electromagnetic).[([[http://books.google.com/books?isbn=9780521816144|J. M. D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, 2010, p. 7]])]
 +
 +{{page>insert/paypal}}
 +
 +<WRAP clear></WRAP>
 +
 +===== Types of magnetism =====
 +
 +|< 100% >|
 +| {{/wiki/logo.png?20&nolink}} //See also the main article: [[Types of magnetisms]].// |
 +
 +<box 30% right #f0f0f0>
 +[[Electric current]] //I// generates [[magnetic field]] //H// 
 +[[/file/electric_current_generates_magnetic_field_magnetica.jpg|{{/electric_current_generates_magnetic_field_magnetica.jpg}}]]
 +{{page>insert/by_SZ}}</box>
 +
 +Moving electric charges or electric current is always a source of [[magnetic field]]. Also, fundamental properties of subatomic particles (such as [[spin magnetic moment]] or [[orbital magnetic moment]]) are sources or magnetic field.
 +
 +All materials respond to the magnetic field in some way. This is also true for those materials which are commonly referred to as "[[non-magnetic material|non-magnetic]]", whose response can be of much lower magnitude as compared to "[[magnetic material|magnetic]]". The magnetic response is also typically affected by other parameters, such as: [[temperature]], [[pressure]] and mechanical [[strain]], [[chemical composition]], [[crystallography]], and many more.[(Materials>[[http://books.google.com/books?isbn=9780495296027|Donald R. Askeland, Pradeep P. Fulay, Wendelin J. Wright, The Science & Engineering of Materials, Cengage Learning, 2011, ISBN 9780495296027, p. 773]])] 
 +
 +<box 30% left #f0f0f0>
 +[[Hysteresis loop]] is a symbol of [[ferromagnetic]] phenomena 
 +[[/file/m4_b-h_loop_50hz.png|{{/m4_b-h_loop_50hz.png}}]]
 +{{page>insert/by_SZ}}
 +</box>
 +
 +A specific class of a response can be categories as a [[type of magnetisms|type of magnetism]], with the three principal ones: 
 +[([[http://boooks.google.com/books?isbn=9780080542713|Roman Boca, Theoretical Foundations of Molecular Magnetism, Current Methods in Inorganic Chemistry, Elsevier, 1999, ISBN 9780080542713, p. 369]])]
 +
 +  * [[paramagnetism]]
 +  * [[diamagnetism]]
 +  * [[ferrromagnetism]] (and other ordered structures)
 +
 +And from theoretical physics point of view these can be further subdivided to over twenty other types, depending on the involved atomic structure, spin ordering, etc.
 +
 +In every day life the materials are often referred to as "magnetic" and "non-magnetic". A simple test is to touch a given material with a [[permanent magnet]] (e.g. a [[fridge magnet]]) - if a mechanical force can be felt (e.g. the magnet "sticks") then the material is "[[magnetic material|magnetic]]". Otherwise it is "[[non-magnetic material|non-magnetic]]". This layperson classification does not follow the same classes as the theoretical - for instance a magnet does not attract [[antiferromagnetism|antiferromagnetic]] material, but it is a magnetically ordered structure.
 +
 +<box 30% right #f0f0f0>
 +[[Geomagnetism]] is a study of [[Earth magnetic field|Earth's magnetic field]] 
 +[[/file/earth_magnetic_field_schematic_magnetica.png|{{/earth_magnetic_field_schematic_magnetica.png}}]]
 +{{page>insert/by_SZ}}
 +</box>
 +
 +Also, there are multiple other terms which are commonly used in relation to other branches of science. These do not refer to phenomena different from those listed above, but strongly linked with the specific scientific or technological area, and with the topic being significant enough so it gained its own name:
 +  * [[electromagnetism]] - branch of physics concerned with analysing magnetic and electric field as a single electromagnetic phenomenon [([[http://books.google.com/books?isbn=9781118723357|I. S. Grant, W. R. Phillips, Electromagnetism, Manchester Physics Series, Wiley, 2013, 9781118723357, (Preface)]])]
 +  * [[biomagnetism]] - magnetic phenomena in living organisms [([[http://books.google.com/books?isbn=9789051992335|Christoph Baumgartner (ed.), Biomagnetism: Fundamental Research and Clinical Applications : Proceedings of the 9th International Conference on Biomagnetism, Volume 7 of Studies in Applied Electromagnetics and Mechanics, IOS Press, 1995, ISBN 9789051992335]])]
 +  * [[geomagnetism]] - study of [[Earth's magnetic field]] [(Gubbins>[[http://books.google.com/books?isbn=9781402044236|David Gubbins, Emilio Herrero-Bervera, (ed.), Encyclopedia of Geomagnetism and Paleomagnetism, Springer, 2007, ISBN 9781402044236]])]
 +  * [[paleomagnetism]] - magnetic properties of geological structures [(Gubbins)]
 +  * [[cryomagnetism]] - magnetic phenomena at very low temperatures [([[http://books.google.com/books?id=V10iGwAACAAJ|Dionysios Elias Speliotis, A Cryomagnetic Study of Iron Oxides, University of Minnesota, 1961, p]])]
 +  *[[micromagnetism]] - magnetic phenomena in small physical structures (e.g. at atomic level) [([[http://books.google.com/books?isbn=9780521331357|Helmut Kronmüller, Manfred Fähnle, Micromagnetism and the Microstructure of Ferromagnetic Solids, Cambridge studies in magnetism, Cambridge University Press, 2003, ISBN 9780521331357]])]
 +  *[[quantum magnetism]] - magnetic phenomena in [[quantum physics]][(Sachdev>[[https://doi.org/10.1038/nphys894|Sachdev, S. Quantum magnetism and criticality. Nature Phys 4, 173–185 (2008), https://doi.org/10.1038/nphys894]])]
 +  * and many more.
 +
 +===== Scales, nature and importance,  =====
 +<box 30% right #f0f0f0>
 +Path of moving [[electron|electrons]] can be bent into a circle by applied [[magnetic field]] 
 +[[file/Cyclotron motion wider view.jpg|{{Cyclotron motion wider view.jpg}}]] 
 +//<sup>by M. Białek, Wikimedia Commons, CC-BY-SA-3.0</sup>// </box>
 +
 +The study of magnetic phenomena extends from [[subatomic particle]]s[([[http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1062609|Trower, W., Magnetic detection of magnetic monopoles, IEEE Transactions on Magnetics, Vol. 19 (5), 1983, p. 2061]])] to cosmic scales.[([[http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1065140|Drukier, A.; Freese, K.; Spergel, D., Detecting "missing mass" candidates with the superheated superconducting detector, IEEE Transactions on Magnetics, Vol. 23 (2), 1987, p. 717]])] [[Electron|Electrons]] (which are responsible for [[ferromagnetism]]) have an estimated [[electron radius|radius]][(Hans Dehmelt, A Single Atomic Particle Forever Floating at Rest in Free Space: New Value for Electron Radius, Physica Scripta, T22, s. 102–110, 1988)] at the level of 10<sup>-22</sup> m (the estimates vary several orders of magnitude, depending on the theoretical or experimental approach) and magnetic-like effects are observed also for structures as large as galaxies[([[http://www.spacetelescope.org/images/heic0817a/|http://www.spacetelescope.org / NGC 1275, {accessed 9 May 2013}]])] with dimensions 10<sup>21</sup> m. Therefore, the magnetic phenomena extend over an extremely wide range of dimensions, and affect nature in multitude ways.
 +
 +There are numerous types of magnetic behaviour, many of them being highly [[non-linear]]. For instance [[ferromagnetism]][([[http://books.google.com/books?isbn=0780310322|Bozorth R.M., Ferromagnetism, IEEE Press, John Wiley & Sons, New York, 2003, ISBN 0-7803-1032-2]])] continues to have a major impact on the evolution of various technologies, mainly through its involvement in energy generation and conversion. Most of the electricity generated worldwide is converted, transmitted and consumed with the use of ferromagnetic and electromagnetic phenomena. 
 +
 +Because of the many interrelated types of magnetic behaviours magnetism is a difficult branch of science, which was recognised by the authors of Encyclopaedia Britannica, who wrote in 1983:[([[http://books.google.com/books?isbn=9780852294000|The New Encyclopaedia Britannica: Macropaedia, Magnetism in solids, Vol. 19, p. 1040, 15th edition, Encyclopaedia Britannica, Chicago 1983, ISBN 9780852294000]])]
 +
 +| //Few subjects in science are more difficult to understand than magnetism.// |
 +
 +<box 40% left #f0f0f0>
 +The thread-like long structures in galaxy [[NGC 1275]] are believed to be caused by magnetic field 
 +[[file/Galaxy NGC 1275 Heic0817a.jpg|{{Galaxy NGC 1275 Heic0817a.jpg}}]]
 +//<sup>by NASA, ESA and A. Fabian, Public domain</sup>//
 +</box>
 +
 +The quote was also used by [[David Jiles]] in his popular book //[[Introduction to Magnetism and Magnetic Materials]]//.[([[http://books.google.com/books?isbn=9780412798603|David C. Jiles, Introduction to Magnetism and Magnetic Materials, Second Edition, Chapman & Hall, CRC, 1998, ISBN 9780412798603]])]
 +
 +On the macroscopic level magnetic field can be analysed as being generated by electric current. However, it was shown that in some materials the magnetic field can be also attributed to a property known as "[[spin]]" of subatomic particles, a phenomenon which cannot be fully explained yet by the the current state of knowledge. Also, electromagnetic waves travel in absence of any matter (e.g. in [[vacuum]]). Hence, a question asked by a student:[(Beckley>[[http://books.google.com/books?isbn=095400390X|Beckley P., Electrical Steels, A Handbook for Producers and Users, European Electrical Steels, Newport, 2000, UK, ISBN 095400390X]])]
 +
 +| //If this space in front of my eyes contains a magnetic field what is in there sustaining it? // |
 +
 +remains without satisfactory answer. Many theories have been proposed by theoretical physicists, but some of them (e.g. the [[superstring theory]]) remain impossible to verify with the current state of science, knowledge and technology.
 +
 +<box 25% right #f0f0f0>
 +[[Lightning]] is a sudden discharge of [[electric current]] which generates an impulse of magnetic field
 +[[file/lightning_pd.jpg|{{lightning_pd.jpg}}]]
 +//<sup>by Nico36, Public Domain</sup>//
 +</box>
 +
 +From practical point of view magnetism is widely used in [[electricity]] [[generator|generation]], [[transformer|transformation]] and consumption. [(Beckley)] Magnetic phenomena are employed in various [[sensor|sensors]], which indirectly influence most branches of science and technology, but there are also a lot of examples of direct use in: 
 +physics[([[http://books.google.com/books?isbn=0198517769|Chikazumi S., Physics of ferromagnetism, 2nd edition, Oxford University Press, Oxford, UK, ISBN 0-19-851776-9]])], electrical engineering[([[http://books.google.com/books?isbn=9780750310383|Tumański S., Principles of Electrical Measurement, Taylor & Francis, CRC Press, 2006, ISBN 9780750310383]])], telecommunication[([[http://books.google.com/books?isbn=0335225551|Gordon A. Gow, Richard K. Smith, Mobile and Wireless Communications, An introduction, Open University Press, New York, 2006, ISBN 0335225551]])]
 +medicine[([[http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1067393|Grob, D.; Stein, P., Magnetism in medicine, IEEE Transactions on Magnetics, Vol. 8 (3), 1972, p. 413]])], biology[([[http://books.google.com/books?isbn=0198506805|D. T. Edmonds, Electricity and Magnetism in Biological Systems, Oxford University Press, 2001, ISBN 0198506805]])], finances[([[http://spectrum.ieee.org/computing/it/financial-trading-at-the-speed-of-light|David Schneider, Financial Trading at the Speed of Light, IEEE Spectrum, Oct 2011]])], space exploration[([[http://spectrum.ieee.org/aerospace/satellites/exploring-space-with-chipsized-satellites|Mason Peck, Exploring Space with Chip-sized Satellites, IEEE Spectrum, Aug 2011]])], computer data storage[([[http://spectrum.ieee.org/semiconductors/memory/spintronic-memories-to-revolutionize-data-storage|Salah M. Bedair, John M. Zavada, Nadia El-Masry, Spintronic Memories to Revolutionize Data Storage, IEEE Spectrum, Nov 2010]])], security[([[http://spectrum.ieee.org/biomedical/ethics/trays-vs-terrorists|John F. Federici, Dale Gary, Robert Barat, Zoi-Heleni Michalopoulou, T-Rays vs. Terrorists, IEEE Spectrum, Jul 2007]])], food production[([[http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1061920|Lindley, J., The use of magnetic techniques in the development of a hydrogenation process, IEEE Transactions on Magnetics, Vol. 18 (3), 1982, p. 836]])] and many more.
 +
 +The plethora of practical applications can be classified by a few basic magnetic and electromagnetic effects, as mentioned throughout this article.
 +
 +In nature, an example of magnetic field generation is a [[lightning]], which is a sudden discharge of [[electric current]] producing an impulse of [[magnetic field]] around itself, as well as electromagnetic waves throughout wide spectrum, including the visible light. Lightnings are capable of magnetising naturally occurring minerals like [[lodestone]], which retained the magnetised state[(Bowles_Minerals>[[https://www.google.co.uk/search?tbo=p&tbm=bks&q=isbn:9781862393158|J. F. W. Bowles, R. A. Howie, D. J. Vaughan, J. Zussman, Rock-forming Minerals, Geological Society of London, 2011, ISBN 9781862393158, p. 403]])]
 + so that humans could discover the phenomenon of magnetism.
 +
 +There are many other mechanisms in which magnetic field can be generated, for example with the core of a planet, on a global level (see: [[Earth magnetic field|Earth's magnetic field]]). 
 +
 +===== Biological =====
 +<box 30% right #f0f0f0>
 +Green leaves perform photosynthesis in plants 
 +[[file/leaf_1_web.jpg|{{leaf_1_web.jpg}}]] 
 +//<sup>by Jon Sullivan, CC-0</sup>//
 +</box>
 +
 +Most of the life forms on Earth are supported by the energy delivered from the Sun in a form of [[/light]] or [[/electromagnetic radiation]]. Plants convert light into chemical energy (such as sugars) in photosynthesis. 
 +
 +Plants are consumed by animals like herbivores, which in turn are consumed by carnivores. Most food chains utilise electromagnetic energy converted initially by green plants.
 +
 +Moreover, even the current state of human technology was originally achieved and is still supported mostly by the same source, which in the past was stored as fossil fuels (like coal, crude oil and natural gas).[(Photosynthesis, Encyclopædia Britannica Ultimate Reference Suite, Chicago: Encyclopædia Britannica, 2013)]
 +
 +Life on the Earth would not be possible to the same extent without the electromagnetic energy. However, there are some primitive organisms which can use other sources of energy (e.g. heat at the ocean floor).
 +
 +However, [[magnetostatic]] field cannot be used as an energy source. But it can be employed for less critical purposes like navigation by birds or other animals.[(Migalski)] 
 +
 +This is one of the reasons why the distinction is made between classical magnetism ([[magnetostatic field|static magnetic fields]]) and [[electromagnetism]] (inseparable combination of changing electric and magnetic fields).
 + 
 +
 +===== Mechanical forces =====
 +
 +|< 100% >|
 +| [[Magnetic force|{{/wiki/logo.png?25}}]] //See separate article on//: [[Magnetic force]] | 
 +
 +Magnetic effects can generate mechanical force, often referred to as [[magnetic force]].
 +
 +[[Permanent magnet|Permanent magnets]] (common name: "magnets") are used widely for generation or conversion of mechanical forces. This is also true for [[electromagnet|electromagnets]], [[electromagnetic actuator|actuators]] and [[magnetic sensor|sensors]]. The mechanical force is then used for working with or against other forces. 
 +
 +Magnets could be used for very high power applications e.g. a [[generator]] in a power plant or [[electric motor]] in propulsion of electric cars, as well as atomic and sub-atomic particles, whose trajectories are affected by the mechanical forces of particle accelerators.
 +
 +A few examples can be given as: 
 +  * [[fridge magnet]] - working with friction against gravity
 +  * [[loudspeaker]] - balancing spring force acting on the membrane
 +  * [[generator]] - generate [[electricity]] from mechanical force
 +  * [[electric motor]] - generate mechanical force from electricity
 +  * [[compass]] - aligning the needle against friction
 +  * [[particle accelerator]] - a charged particle path is deflected in magnetic field (this includes applications like [[CRT]] or [[Aurora Borealis]] in which charged particles are guided by the [[geomagnetic field]])
 +  * [[ferrofluid]] - mechanical forces act on the particles suspended in a fluid and change its behaviour (e.g. against gravity)
 +  * [[magnetic levitation]]
 +  * [[magnetic bearing]]
 +  * [[microwave heating]] - mechanical movement of water particles generates heat through mechanical friction
 +
 +<WRAP>
 +<box 30% left #f0f0f0>
 +[[Electric motor]] converts electricity to mechanical energy 
 +[[file/electric_motor_magnetica.jpg|{{electric_motor_magnetica.jpg}}]] 
 +// {{page>insert/by_SZ}} //
 +</box>
 +<box 30% left #f0f0f0>
 +Permanent magnets are used in [[electric motor|motors]], [[generator|generators]], [[electromagnetic actuator|actuators]], [[loudspeaker|loudspeakers]], toys, etc.
 +[[file/hard_ferrites_1_magnetica.jpg|{{hard_ferrites_1_magnetica.jpg}}]] 
 +// {{page>insert/by_SZ}} //
 +</box>
 +<box 30% left #f0f0f0>
 +[[Deflection coil|Deflection coils]] in a [[CRT]] affect trajectory of charged particles 
 +[[file/deflection_coils_1_magnetica.jpg|{{deflection_coils_1_magnetica.jpg}}]] 
 +// {{page>insert/by_SZ}} //
 +</box>
 +</WRAP>
 +
 +===== Electromagnetic energy conversion =====
 +<box 30% right #f0f0f0>
 +[[Power transformer]] is a crucial part of electric grid 
 +[[file/High-voltage in Iraq.jpg|{{High-voltage in Iraq.jpg}}]]
 +//<sup>by Marvin L. Daniels, U.S. Army, Public domain</sup>//
 +</box>
 +
 +[[Electromagnetism]] is used for [[electromagnetic coupling]] of energy between the source and the load. Although some mechanical effect can be generated during the operation (e.g. [[magnetostriction]]) the energy is converted primarily through non-moving parts, due to the laws of [[electromagnetic induction]]. This is therefore a different application from motors and generators. Examples:
 +  * [[transformer]] - converting one level of variable current to a different level
 +  * [[wireless charger]] - delivering energy in a contactless way
 +
 +There are also other physical phenomena, which can transfer electromagnetic energy into different type of energy (e.g. heat) but the electromagnetic-electromagnetic conversion is a special case, and it is currently used as the pivotal component of global [[grid]] supplying [[electricity]]. This is possible because the transformers can increase the voltage to very high level for more efficient transmission of [[electricity]]. At the same time the transformers are very efficient devices, with figures up 99% for high-power devices.
 +[([[http://books.google.com/books?isbn=9781848826670|Pavlos S. Georgilakis, Spotlight on Modern Transformer Design, Power Systems, Springer, 2009, ISBN 9781848826670, p. 4]])]
 +
 +Another inherent feature of electromagnetic conversion is that it allows [[galvanic separation]] between the circuits, which is a very important factor from the viewpoint of safety of electric circuits. [([[http://books.google.com/books?isbn=9781118211519|Elya B. Joffe, Kai-Sang Lock, Grounds for Grounding: A Circuit to System Handbook, John Wiley & Sons, 2011, ISBN 9781118211519]])] For example, mains-powered chargers for portable appliances (such as mobile phones, tablets, laptops) are not required to have connection to [[earth|ground/earth]] only if they have full galvanic isolation between the mains input and the low-voltage output.[(IEC>[[https://webstore.iec.ch/publication/23997|EC 61140:2016, Protection against electric shock - Common aspects for installation and equipment]], {accessed 2020-07-17})]
 +
 +===== Thermal effects =====
 +<box 30% right #f0f0f0>
 +[[Induction heating]] of a metal bar 
 +[[file/Induction heating of bar Commons.jpg|{{Induction heating of bar Commons.jpg}}]] 
 +//<sup>by Vector1 nz, [[https://creativecommons.org/licenses/by-sa/3.0/|CC-BY-SA-3.0]]</sup>//
 +</box>
 +
 +There are several applications in which magnetism is used for creating thermal effects. Only few of these exhibit a direct link between magnetic field and thermal phenomena, rather than having an intermediate electromagnetic-electromagnetic coupling. 
 +
 +Cooling can be achieved by adiabatic demagnetisation through the [[magnetocaloric effect]]. In theory it should be possible to build efficient [[magnetic refrigeration|magnetic refrigerators]], without any moving parts. Research is carried out to find appropriate materials and configurations which could facilitate commercially viable devices.[([[http://dx.doi.org/10.1063/1.1451906|S. J. Lee, J. M. Kenkel, V. K. Pecharsky, and D. C. Jiles, Permanent magnet array for the magnetic refrigerator, Journal of Applied Physics, Vol. 91 (10), 2002, p. 8894]])]
 +
 +Examples:
 +  * [[magnetocaloric effect]] - cooling through [[demagnetisation]]
 +  * [[Nernst effect]] - generation of temperature gradient due to [[magnetic field]]
 +
 +Other magneto-thermal effects rely on some intermediate physical phenomena to generate heat. For instance, electric current is induced in any conducting medium which is exposed to a varying magnetic field. These so-called [[eddy current|eddy currents]] are capable of heating up the medium in which they flow, and it is a basis for all [[induction heating]] devices. However, it is the eddy currents which are ultimately the source of heat - so electromagnetism is used only to transfer the energy and induce the currents.
 +
 +Examples:
 +  * [[induction heating]] - heating by inducing [[eddy currents]]
 +  * [[microwave heating]] - heating by friction due to mechanical movements of water particles
 +
 +===== Electromagnetic waves =====
 +
 +|< 100% >|
 +| {{/wiki/logo.png?20&nolink}} //See also the main article: [[Electromagnetic waves]].// |
 +
 +<box 25% right #f0f0f0>
 +Mobile phones use [[electromagnetic waves]] to transmit and receive signals 
 +[[file/Mobile phone evolution.jpg|{{Mobile phone evolution.jpg}}]]
 +//<sup>by Anders K. Larsen, Public domain</sup>//
 +</box>
 +
 +Each variation of magnetic field or electric field in time produces electromagnetic waves. Such electromagnetic radiation is referred to as [[electromagnetism]] and for instance can be analysed as the so-called [[near field]] or [[far field]] phenomena. In electric and electronic circuits there can be [[transmission line]] effects, which are caused by the link between the [[wave length]] and physical circuit dimensions.
 +
 +A whole important sub-class of magnetic phenomena is transmission of signals through electromagnetic waves. For efficient transmission [[tuned circuit|tuned circuits]] are used, and are ubiquitously employed in terrestrial and outer space telecommunication.
 +
 +Examples:
 +  * [[tuned circuit]] - a basis for all signal transmission based on electromagnetic waves of various length (from [[radio waves]], through [[GPS]] and [[mobile phone]] [[telecommunication]], to [[radar]], and beyond)
 +  * [[radar]] - detection of signals reflected from objects
 +  * [[X-ray]] - inner structure of materials or bodies can be detected due to differences in absorption of electromagnetic waves
 +
 +<box 25% left #f0f0f0>
 +X-ray image of human chest taken for medical purposes
 +[[file/x-ray_of_child_chest_fda_public_domain_.jpg|{{x-ray_of_child_chest_fda_public_domain_.jpg}}]]
 +//<sup>FDA, Public Domain</sup>//
 +</box>
 +Transmission of signals is actually also transmission of energy, but with smaller power. The same principles can be used for transmission of energy, for instance in some types of wireless charging.
 +
 +At much higher frequencies the electromagnetic waves constitute visible spectrum, so that all optical devices in effect employ electromagnetic waves in the form of invisible ([[infra-red]], [[ultraviolet]]) and [[visible light]] (see next section).
 +
 +===== Optical =====
 +<box 30% right #f0f0f0>
 +Fire flames are a display of electromagnetic waves 
 +[[file/Fire flames.jpg|{{Fire flames.jpg}}]] 
 +//<sup>by J. Sullivan, Public domain</sup>//
 +</box> 
 +
 +Other optical effects are related to [[electromagnetic wave|electromagnetic waves]], but with specific range of [[wavelength|wavelengths]]. 
 +
 +Visible [[light]] can be generated in a number of ways: from thermal heating (burning flame, incandescent light bulb), through [[electroluminescence]] (light-emitting diode), [[ionising|ionised]] gasses (compact [[fluorescence|fluorescent]] light bulb), chemical reactions, [[bioluminescence]], etc.
 +
 +<box 30% left #f0f0f0>
 +A rainbow is an example of spectrum of visible [[light]] 
 +[[file/Double rainbow.jpg|{{Double rainbow.jpg}}]] 
 +//<sup>by A. McMillan, Public domain</sup>//
 +</box>
 +
 +Visible and near-visible spectrum is suitable for a whole range of applications: energy transfer ([[photovoltaic effect|photovoltaic]] cells), heat generation (infrared halogen heaters), signal and information transmission (traffic lights, fibre optic computer networks), sensing (all optical sensors), [[laser|lasers]], and many many more.
 +
 +[[Optics]] itself its a very wide scientific and technological field and is a separate branch of physics, but because of its diversity in its own right it overlaps with almost every aspect of science and technology. 
 +
 +Interestingly, there are also direct phenomena occurring between light (electromagnetic waves) and magnetic or electromagnetic fields. For instance in the [[Faraday effect]] magnetic field can twist a polarised beam of light, and there are scientific indications that the vision of pigeons is affected by Earth's magnetic field.[(Migalski>[[http://toc.proceedings.com/05647webtoc.pdf|S. Migalski, et al., Developing a Behavioural Assay of Magnetic Field Sensitivity in Homing Pigeons: Is it a Question of Vision?, Orientation & Navigation: Birds, Humans and Other Animals Conference, Royal Institute of Navigation, 2008, {accessed 2 Jul 2013}]])]
 +
 +===== Sensors and transducers =====
 +<box 30% right #f0f0f0>
 +[[Compass]] detects direction of [[Earth's magnetic field]] 
 +[[file/Compass Magnetica.jpg|{{Compass Magnetica.jpg}}]] 
 +{{page>insert/by_SZ}} 
 +</box>
 +
 +A multiplicity of other physical quantities can be measured by employing phenomena related to [[magnetics]]. In [[sensor|sensors]] and [[transducer|transducers]] the amount of processed energy is usually small, and focus is given to such aspects as accuracy and [[linearity]] of signal transformation, rather than [[efficiency]] of energy conversion. 
 +
 +<box 30% left #f0f0f0>
 +[[Fluxgate magnetometer]] is a [[sensor]] of [[magnetic field]]
 +[[file/Fluxgate magnetometer commercial.jpg|{{Fluxgate magnetometer commercial.jpg}}]] 
 +{{page>insert/by_SZ}} 
 +</box>
 +
 +Examples:
 +  * [[Hall effect]] - output voltage is proportional to the input [[magnetic field]] (or electric current which produces it)
 +  * [[Faraday effect]] - light twisting angle is proportional to the input [[magnetic field]] (or electric current)
 +  * [[fluxgate magnetometer]] - asymmetry of magnetic saturation of one element can be used as a basis for measurement of magnetic field from a different source (e.g. electric current)
 +  * [[Kerr effect]] - [[magnetic domain wall]] movements can be used as a detector of magnetic field (or electric current)
 +  * [[compass]] - sensing direction of [[Earth's magnetic field]]
 +  * [[magnetic resonance imaging]] - electromagnetic field generated by protons can be used for construction of 3D images of inside of living organisms in a non-invasive way
 +
 +===== Information storage =====
 +
 +<box 30% right #f0f0f0>
 +[[Hard drive]] uses magnetic technology to store digital information 
 +[[file/Hard drive with IDE Magnetica.jpg|{{Hard drive with IDE Magnetica.jpg}}]] 
 +{{page>insert/by_SZ}} 
 +</box>
 +
 +Magnetism is still widely used as a major technology for information storage. A layer of [[ferromagnetic substance]] can be magnetised, and the direction of [[local magnetisation]] can store information in an analogue or digital way. 
 +
 +Magnetism and [[electromagnetism]] are widely used for such applications, because they offer inexpensive way of manufacturing such products. Importantly, it is possible to have completely contactless interaction, for instance in anti-theft protection systems. 
 +
 +Examples:
 +  * [[magnetic tape]] ([[music cassette]] and [[video tape]])
 +  * [[hard disk]]
 +  * [[anti-theft protection]]
 +
 +===== History of magnetism =====
 +
 +|< 100% >|
 +| {{/wiki/logo.png?20&nolink}} //See separate article on//: [[History of electromagnetism]] | 
 +
 +
 +===== References =====
 +~~REFNOTES~~
 +
 +{{tag>Magnetism Counter}}

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