Electromagnetism

Credibility in a scientific community (sensu Shapin) is a vicarious selector (sensu Campbell) for the reliability of reports by individual scientists or institutions. Similarly, images from a microscope (sensu Hacking) are vicarious selectors for studying specimens. Working at different levels, the process of indirect reasoning and checking indicates a unity to experimentalist and sociological perspectives, along with a resonance of strategies for assessing reliability. The perspective sketched here can open dialogue between philosophical and sociological interpretations of science and resolves at (...) least one tension regarding the "primary" factors by which scientists evaluate claims. (shrink)

In the past the particle-wave duality of electromagnetic waves dominated the discussions about the nature of light. No consensus had been reached amongst physicists and philosophers of physics concerning which interpretation represents reality best. However, two different concepts for the same phenomenon doesn’t really convince about the reliability of the conceptual framework. So what is wrong?

Reflectance physicalists define reflectance as the intrinsic disposition of a surface to reflect light at a given efficiency per wavelength. I criticize a leading account of dispositional reflectance for failing to account for what I call 'harmonic dispersion', the inverse relationship of a light pulse's duration to its bandwidth. I argue that harmonic dispersion renders reflectance defined in terms of light pulses an extrinsic disposition. Reflectance defined as the per-wavelength efficiency to reflect the superimposed, infinite-duration, Fourier harmonics of pulses can (...) be an intrinsic disposition of surfaces. This conclusion raises questions about mathematical realism, about which I nevertheless remain neutral. (shrink)

Abstract We examine the construction of electromagnetism in its current form, and in an alternative form, from a point of view that combines a minimal realism with strict rational demands. We begin by discussing the requests of reason when constructing a theory and next, we follow the historical development as presented in the record of original publications, the underlying epistemology (often explained by the authors) and the mathematical constructions. The historical construction develops along socio-political disputes (mainly, the reunification of Germany (...) and the second industrial revolution), epistemic disputes (at least two demarcations of science in conflict) and several theories of electromagnetism. Such disputes resulted in the militant adoption of the ether by some, a position that expanded in parallel with the expansion of Prussia. This way of thinking was facilitated by the earlier adoption of a standpoint that required, as a condition for understanding, the use of physical hypothesis in the form of analogies; an attitude that is antithetic to Newton's “hypotheses non fingo”. While the material ether was finally abandoned, the epistemology survived in the form of “substantialism” and a metaphysical ether: the space. The militants of the ether attributed certainties regarding the ether to Faraday and Maxwell, when they only expressed doubts and curiosity. Thus, the official story is not the real history. This was achieved by the operation of detaching Maxwell's electromagnetism from its construction and introducing a new game of formulae and interpretations. Large and important parts of Maxwell work are today not known, as for example, the rules for the transformation of the electromagnetic potentials between moving systems. When experiments showed that all the theories based in the material ether were incorrect, a new interpretation was offered: Special Relativity (SR). At the end of the transformation period a pragmatic view of science, well adapted to the industrial society, had emerged, as well as a new protagonist: the theoretical physicist. The rival theory of delayed action at distance initiated under the influence of Gauss was forgotten in the midst of the intellectual warfare. The theory is indistinguishable in formulae from Maxwell's and its earlier versions are the departing point of Maxwell for the construction of his equations. We show in a mathematical appendix that such (relational) theory can incorporate Lorentz' contributions as well as Maxwell's transformations and C. Neumann's action, without resource to the ether. Demarcation criteria was further changed at the end of the period making room for habits and intuitions. When these intuited criteria are examined by critical reason (seeking for the fundaments) they can be sharpened with the use of the Non Arbitrariness Principle, which throws light over the arbitrariness in the construction of SR. Under a fully rational view SR is not acceptable, it requires to adopt a less demanding epistemology that detaches the concept from the conception, such as Einstein's own view in this respect, inherited from Hertz. In conclusion: we have shown in this relevant exercise how the reality we accept depends on earlier, irrational, decisions that are not offered for examination but rather are inherited from the culture. (shrink)

Computational neuroscience attributes coloured areas and other perceptual qualia to calculations that are realizable in multiple cellular forms. This faces serious issues in explaining how the various qualia arise and how they bind to form overall perceptions. Qualia may instead be neuroelectrical. Growing evidence indicates that perceptions correlate with neuroelectrical activity spotted by locally activated EEGs, the different qualia correlate with the different electrochemistries of unique detector cells, a unified neural-electromagnetic field binds this activity to form overall perceptions, and this (...) field interacts with sensory circuits to help attentively guide perception. The coloured areas in images may thus be seated in the electrochemistry of unique cells, while constancy mechanisms and other multiply realizable computations just help refine these images behind the scenes. This theory is ultimately testable. (shrink)

Previzualizare carte -/- O introducere în fenomenologia opticii geometrice (reflexia, refracția, principiul lui Fermat, oglinzi, miraje, dispersia, lentile), opticii fizice (undele luminoase, principiul Huygens–Fresnel, difracția, interferența, polarizarea, vederea tridimensională, holografia), opticii cuantice (fotoni, efectul fotoelectric, dualitatea undă-particulă, principiul incertitudinii, complementaritatea) și culorilor (transparența, translucența, amestecul culorilor, culori complementare, pigmenți), în conexiune cu teoriile fundamentale ale luminii. Despre proprietățile luminii (unde electromagnetice, spectrul electromagnetic, materiale transparente și opace, umbra, sistemul vizual uman, lumina Soarelui) și emisia luminii (stări excitate, spectrele de emisie (...) și absorbție, incandescența, fluorescența, fosforescența, LED, laser). Cartea explică bazele fizice pentru înțelegerea fenomenelor optice, cu accent pe fenomenele naturale și aplicațiile specifice. -/- CUPRINS: -/- Lumina - Optica fenomenologică Proprietățile luminii - Unde electromagnetice - - Viteza undelor electromagnetice - - - Viteza luminii - Spectrul electromagnetic - - Intervalul spectrului - - Argumentare pentru denumirile regionale ale spectrului - Materiale transparente - - Ceramica transparentă - - Transparența în izolatori - - Camuflaje - Materiale opace (Opacitatea) - - Radioopacitatea - - Definiție cantitativă - Umbra - - Surse de lumină punctuale și non-punctuală - - Astronomie - - Variația în timpul zilei - - Viteza de propagare - - Culoare - - Umbre tridimensionale - - În fotografie - Sistemul vizual uman (Ochiul) - - Ochiul uman - - Retina - - Vedere binoculară - De ce este apusul de Soare roșu? - De ce sunt norii colorați? - Ce culoare are apa? - - Culoarea intrinsecă - - Culoarea lacurilor și a oceanelor - - Culoarea ghețarilor - - Culoarea probelor de apă Culori - Reflexia selectivă (Culoarea unui obiect) - - Culoarea obiectelor - - Difuzia culorilor - Transmiterea selectivă (Transparența și translucența) - - Împrăștierea luminii în solide - - Absorbția luminii în solide - Amestecul luminii colorate (Amestecul culorilor) - - Amestecul aditiv - - Amestecul subtractiv - Culori complementare - - Culori complementare - - În diferite modele de culori - - - Model tradițional de culoare - - Culorile produse de lumină - - Imprimarea culorilor - - Persistența imaginii - - Aplicații practice - Amestecul pigmenților colorați (Pigmenți) - - RYB - - Procese de imprimare CMY și CMYK - - Amestecarea subtractivă a straturilor de cerneală - - Amestecarea vopselelor în palete limitate - De ce e cerul albastru? - - Radiația difuză a cerului - - Împrăștierea Rayleigh - - De ce e cerul albastru Reflexia și refracția (Optica geometrică) - Istorie - Reflexia - - Reflexia luminii - Principiul timpului cel mai scurt (Principiul lui Fermat) - - Derivare - - Istorie - Legea reflexiei - - Formula vectorială - - Reflectivitate - - Consecințe - - - Reflecția internă - - - Polarizare - - - Imagini reflectate - - Exemple - Oglinzi plane (Oglinzi) - - Efecte - - - Forma suprafeței unei oglinzi - - - Imagine în oglindă - - Oglinzi plane - - - Preparare - - - Relația cu oglinzile curbate - Reflexia difuză - - Mecanism - - Obiecte colorate - - Importanța pentru vedere - - Interreflexia - Refracția - - Explicaţie - Mirajul - - Mirajul inferior - - - Încețoșarea - - Mirajul superior - - - Fata Morgana - - Miraje de noapte - - - Miraje ale obiectelor astronomice - Dispersia - - Exemple - - Dispersia materialelor - Curcubeul - - Prezentare generală - - Numărul de culori în spectru sau curcubeu - - Explicaţie - Reflexia internă totală - - Explicația optică - - Unghiul critic - - Reflexia internă totală eșuată - - Schimbarea de fază la reflexia internă totală - Lentile - - Construcția lentilelor simple - - - Tipuri de lentile simple - - Ecuația lui Lensmaker - - - Convenția de semn pentru razele de curbură R1 și R2 - - - Aproximarea lentilelor subțiri - - Lentile compuse - Formarea imaginilor prin lentile - - Mărirea - Defecte ale lentilelor - - Aberații sferice - - Coma - - Aberația cromatică - - Alte tipuri de aberații - - Difracția diafragmei Undele luminoase (Optica fizică) - Principiul Huygens–Fresnel - - Istorie - - Teoria lui Huygens și funcția de undă fotonică modernă - - Principiul lui Huygens și teoria câmpului cuantic - - În alte dimensiuni spațiale - Difracția luminii - - Exemple - - Mecanism - - Difracția luminii - - - Difracția printr-o singură fantă - Interferența optică - - Cerințele sursei de lumină - - Dispozitive optice - - Interferometria optică - Interferența pe straturi subțiri - - Teorie - - Sursă monocromatică - - Sursa de bandă largă - - Interacțiunea de fază - - Aplicații - Polarizarea - - Propagarea și polarizarea undelor - - - Unde electromagnetice transversale - - - Unde netransversale - - Starea de polarizare - - - Elipsa de polarizare - - Polarizarea fotonilor - Vederea tridimensională (Percepția în adâncime) - - Indicii monoculare - - Indici binoculare - - Percepția tridimensională în artă - Holografia - - Cum funcționează - - - Laser - - - Aparatura - - - Procesul - - - Vs. fotografie - - Fizica holografiei - - - Fronturile de undă plane - - - Surse punctuale - - - Obiecte complexe Emisia luminii (Surse de lumină) - Excitarea (Stări excitate) - Spectrul de emisie al luminii - - Emisie - - Origini - - Radiații din molecule - Incandescența - - Observații și utilizare - Spectrul de absorbție (Spectroscopia de absorbție) - - Teorie - - Relația cu spectrul de transmisie - - Relația cu spectrul de emisie - - Relația cu spectrul de dispersie și reflecție - - Spectroscopia de absorbție - Fluorescența - - Principii fizice - - - Fotochimie - - - Randament cuantic - - - Durata de viață - - - Diagrama Jablonski - - Anizotropia fluorescenței - - - Fluorența - - Reguli - - - Regula lui Kasha - - - Regula imaginii în oglindă - - - Deplasarea Stokes - Lămpi fluorescente - - Principiile de funcționare - - - Construcție - - - Aspecte electrice ale funcționării - - - Efectul temperaturii - - Fosforul și spectrul luminii emise - Fosforescența - - Explicaţii - - - Mecanica cuantică - - - Ecuaţia - - Chimiluminescență - - Materiale - LED - - Istorie - - Principiul de funcționare - - Tehnologie - - Fizica - - - Indicele de refracție - Lămpi cu LED - - Istorie - - Tehnologia - - Eficiența - Laser - - Concepte de bază - - - Terminologie - - Construcţia unui laser - - Fizica laserilor - - Aplicaţii - - - Științifice - - - Spectroscopie - - - Tratament termic - - - Reflector lunar cu laser - - - Fotochimie - - - Scanere de coduri de bare laser - - - Răcire cu laser - - - Fuziunea nucleară - - - Microscopie - Extreme Light Infrastructure - - Istorie - - Centrul de cercetare ELI NP Cuanta de lumină (Fotoni) - Proprietăți fizice - Optica cuantică - Nașterea teoriei cuantice (Optica cuantică) - - Istoria opticii cuantice - - Concepte ale opticii cuantice - - Electronica cuantică - Cuantificarea și constanta lui Planck - - Metode de cuantificare - - - Cuantificarea canonică - - Constanta lui Planck - - - Valoare - - - Semnificația valorii - Efectul fotoelectric - - Mecanismul de emisie - - Observații experimentale ale emisiei fotoelectrice - - Descrierea matematică - - Utilizări și efecte - - - Fotomultiplicatori - - - Senzori de imagine - - - Electroscop cu frunză de aur - - - Spectroscopie fotoelectronică - - - Nave spațiale - - - Praful lunar - - - Dispozitive de vedere pe timp de noapte - Dualitatea undă-particulă - - Tratamentul în mecanica cuantică modernă - - Vizualizare - - Aplicarea la modelul Bohr - Experimentul celor două fante - - Prezentare generală - - Interpretările experimentului - - - Interpretarea de la Copenhaga - - - Formularea integrală a căii - - - Interpretarea relațională - - - Interpretarea multiplelor-lumi - Difracția electronilor - - Proprietăți cuantice - - Difracția electronilor - - Interacțiunea electronilor cu materia - - Microscop cu electroni de transmisie - Principiul incertitudinii - - Definire - - Utilizare - Complementaritatea - - Conceptul - - Natura - - Considerații suplimentare - - Experimente Referințe Despre autor - Nicolae Sfetcu - - De același autor - - Contact Editura - MultiMedia Publishing. 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I will present a refutation of 6 and 7 inconsistency claim. Using the proof by Kiessling, I will show that Classical Electrodynamics can be applied consistently and can preserve energy conservation to the problem of charged, accelerated particles. This refutes the core of Frisch's inconsistency claim. Additionally, I will argue that Frisch's proof and the resulting debate is based on a comparison of different, approximate, explicit solutions to the Maxwell–Lorentz equations. However, in order to be informative on the foundations of (...) CED, an analysis would have to be focussed on the Maxwell–Lorentz equations as coupled system of equations. (shrink)

The term “analogy” stands for a variety of methodological practices all related in one way or another to the idea of proportionality. We claim that in his first substantial contribution to electromagnetism James Clerk Maxwell developed a methodology of analogy which was completely new at the time or, to borrow John North’s expression, Maxwell’s methodology was a “newly contrived analogue”. In his initial response to Michael Faraday’s experimental researches in electromagnetism, Maxwell did not seek an analogy with some physical system (...) in a domain different from electromagnetism as advocated by William Thomson; rather, he constructed an entirely artificial one to suit his needs. Following North, we claim that the modification which Maxwell introduced to the methodology of analogy has not been properly appreciated. In view of our examination of the evidence, we argue that Maxwell gave a new meaning to analogy; in fact, it comes close to modeling in current usage. (shrink)

The introduction of electron microscopy profoundly altered biomedical research, providing a tool for a more detailed but at the same time a spatially and temporally more restricted visual analysis. Examining the case study of Golgi apparatus research in the 1950s and 1960s, it will be shown how microscopists handled these challenges, and how these confrontations modified the general concept of cellular organization. This will also shed light on the artifact debate and on the question of scientific realism in the field (...) of microscopy. (shrink)

La posición inicial de Einstein con respecto al éter electromagnético y su posterior eliminación del escenario de la relatividad especial resultaron profundamente alteradas por la relatividad general. En este artículo analizamos los diferentes argumentos de Einstein contra el éter electromagnético. Luego estudiamos las razones que lo llevaron a reintroducir el éter gravitatorio en la relatividad general. Después de comparar las propiedades y funciones del antiguo éter con las del nuevo éter relativista, concluimos que se ha producido un cambio conceptual y (...) que el término "éter" ha experimentado un cambio de significado. No obstante, mostramos que el nuevo éter retuvo algunas de las propiedades y funciones características del viejo éter electromagnético. Einstein's initial attitude towards electromagnetic ether in special relativity was deeply disrupted by general relativity. In this paper we analyze Einstein's different arguments against electromagnetic ether in the frame of special relativity. We then study his reasons for postulating a gravitatory ether in general relativity. After comparing the properties and functions of the traditional electromagnetic ether with those of the new relativistic ether, we conclude that a conceptual change has occurred, because the term "ether" has undergone a change of meaning. However, we also show that the new ether still retains many properties and functions characteristic of the old electromagnetic ether. (shrink)

The place of Heinrich Hertz’s The principles of mechanics in the history of the philosophy of science is disputed. Here I critically assess positivist interpretations, concluding that they are inadequate.There is a group of commentators who seek to align Hertz with positivism, or with specific positivists such as Ernst Mach, who were enormously influential at the time. Max Jammer is prominent among this group, the most recent member of which is Joseph Kockelmans. I begin by discussing what Hertz and Mach (...) had to say about one another, and I specify certain respects in which their views are indeed similar. I then go on to detail their differences, looking at Hertz’s attitude to the atomic theory, to the mechanical world-view, to simplicity, to unobservables and metaphysics, and his objections to Newtonian forces. I conclude that the positivist interpretation of Hertz’s mechanics significantly overplays its similarities to Mach’s views.Keywords: Ernst Mach; Heinrich Hertz; Mechanics; Positivism; Atomism; Force; Metaphysics. (shrink)

We continue our discussion of the competing arguments in favour of the unified theory and the pluralistic theory of radiation advanced by three nineteenth-century pioneers: Herschel, Melloni, and Draper. Our narrative is structured by a consideration of the epistemic criteria relevant to theory-choice; the epistemic focus highlights many little-known aspects of this relatively well-known episode. We argue that the acceptance of light-heat unity in this period cannot be credibly justified on the basis of common evaluative criteria such as simplicity and (...) standard notions of explanatory power. Whether the consensus was justified by some other criteria remains an open question.Keywords: Theory-choice; Epistemic values; Radiation; Simplicity; Explanatory power; Causal explanation. (shrink)

The facts concerning the occurrence of superconductivity in R 2- z Ce z CuO 4 and in R 2- z Th z CuO 4 are studied using a combination of simple tools: a hard-sphere model, the self-consistent bond-valence-sum method and Madelung potential calculations. Doping by isolated substitutional Ce should produce Ce 3+ , and not Ce 4+ , causing us to conclude that the dopants are not isolated, but pairs, which make the material p type and not n type. The (...) L = 0 magnetic rare-earth ions Gd and Cm are unsplit pair breakers, unlike the other magnetic rare-earth ions which lead to superconductivity. As the rare-earth ions become smaller, the c -axis length shortens; then the O ions rotate after they come into contact with one another. Eu 1.85 Th 0.15 CuO 4 does not superconduct because quadrivalent Th is too large to fit at the dopant site, but Eu 1.85 Ce 0.15 CuO 4 does superconduct because Ce fits. (shrink)

The phase field microelasticity theory of a three-dimensional, elastically anisotropic system of voids and cracks is proposed. The theory is based on the equation for the strain energy of the continuous elastically homogeneous body presented as a functional of the phase field, which is the effective stress-free strain. It is proved that the stress-free strain minimizing the strain energy of this homogeneous modulus body fully determines the elastic strain and displacement of the body with voids and/or cracks. The proposed phase (...) field integral equation describing the elasticity of an arbitrary system of voids and cracks is exact. The geometry and evolution of multiple voids and/or cracks are described by the phase field, which is the solution of the time-dependent Ginzburg-Landau equation. Other defects, such as dislocations and precipitates, are trivially integrated into this theory. The proposed model does not impose a priori constraints on possible void and crack configurations or their evolution paths. Examples of computations of elastic equilibrium of systems with voids and/or cracks and the evolution of cracks under applied stress are considered. (shrink)

The first models for an electromagnetic theory of dispersion are presented and an attempt is made to demonstrate the important role played by study of this phenomenon at the end of the nineteenth century. As well as indicating the need to have a better understanding of the microscopic properties of matter, dispersion also contributed to the discussion over the nature of X-rays and was fundamental for introduction of Lorentz's electron theory.

We consider an electron in a 1 D random adiabatically changing potential. We demonstrate that the positions of the maxima of an electron eigenstate probability density do not move even when the change of the potential is significant. We show that at the same time the main maximum hops by a distance of the order of the size of the system. We present arguments that such hopping of electron localization position happens also in two and three dimensions.

THE DANISH chemist and physicist Hans Christian Oersted (1777-I 851) is recognized by historians of science primarily as the discoverer of electromagnetism. His experiments in 1820 demonstrated a definite lawlike relationship between electrical and magnetic phenomena. The quite general question of whether there is in science such a thing as a “logic of discovery” can in this case be given a more precise formulation. Why was Oersted, rather than another of the many scientists interested in electricity and magnetism in the (...) nineteenth century, the fortunate one to have made the discovery, and thus to have his name immortalized in the history of science? What events, ideas, or methods were responsible for the discovery? (shrink)