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Huygens–Fresnel Principle
The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel) states that every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere. The sum of these spherical wavelets forms a new wavefront. As such, the Huygens-Fresnel principle is a method of analysis applied to problems of luminous wave propagation both in the far-field limit and in near-field diffraction as well as reflection. History In 1678, Huygens proposed that every point reached by a luminous disturbance becomes a source of a spherical wave; the sum of these secondary waves determines the form of the wave at any subsequent time. He assumed that the secondary waves travelled only in the "forward" direction and it is not explained in the theory why this is the case. He was able to provide a qualitative explanation of linear and spherical wave propagation, and to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Refraction - Huygens-Fresnel Principle
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomenon, but other waves such as sound waves and water waves also experience refraction. How much a wave is refracted is determined by the change in wave speed and the initial direction of wave propagation relative to the direction of change in speed. For light, refraction follows Snell's law, which states that, for a given pair of media, the ratio of the sines of the angle of incidence ''θ1'' and angle of refraction ''θ2'' is equal to the ratio of phase velocities (''v''1 / ''v''2) in the two media, or equivalently, to the refractive indices (''n''2 / ''n''1) of the two media. :\frac =\frac=\frac Optical prisms and lenses use refraction to redirect light, as does the human eye. The refractive index of materials varies with the wavelengt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
David A
David (; , "beloved one") (traditional spelling), , ''Dāwūd''; grc-koi, Δαυΐδ, Dauíd; la, Davidus, David; gez , ዳዊት, ''Dawit''; xcl, Դաւիթ, ''Dawitʿ''; cu, Давíдъ, ''Davidŭ''; possibly meaning "beloved one". was, according to the Hebrew Bible, the third king of the United Kingdom of Israel. In the Books of Samuel, he is described as a young shepherd and harpist who gains fame by slaying Goliath, a champion of the Philistines, in southern Canaan. David becomes a favourite of Saul, the first king of Israel; he also forges a notably close friendship with Jonathan, a son of Saul. However, under the paranoia that David is seeking to usurp the throne, Saul attempts to kill David, forcing the latter to go into hiding and effectively operate as a fugitive for several years. After Saul and Jonathan are both killed in battle against the Philistines, a 30-year-old David is anointed king over all of Israel and Judah. Following his rise to power, Dav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Melvin Schwartz
Melvin Schwartz (; November 2, 1932 – August 28, 2006) was an American physicist. He shared the 1988 Nobel Prize in Physics with Leon M. Lederman and Jack Steinberger for their development of the neutrino beam method and their demonstration of the doublet structure of the leptons through the discovery of the muon neutrino. Biography He was Jewish. He grew up in New York City in the Great Depression and went to the Bronx High School of Science. His interest in physics began there at the age of 12. He earned his B.A. (1953) and Ph.D. (1958) at Columbia University, where Nobel laureate I. I. Rabi was the head of the physics department. Schwartz became an assistant professor at Columbia in 1958. He was promoted to associate professor in 1960 and full professor in 1963. Tsung-Dao Lee, a Columbia colleague who had recently won the Nobel prize at age 30, inspired the experiment for which Schwartz received his Nobel. Schwartz and his colleagues performed the experiments whic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Near And Far Field
The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative ''near-field'' behaviors dominate close to the antenna or scattering object, while electromagnetic radiation ''far-field'' behaviors dominate at greater distances. Far-field E (electric) and B (magnetic) field strength decreases as the distance from the source increases, resulting in an inverse-square law for the radiated ''power'' intensity of electromagnetic radiation. By contrast, near-field E and B strength decrease more rapidly with distance: the radiative field decreases by the inverse-distance squared, the reactive field by an inverse-cube law, resulting in a diminished power in the parts of the electric field by an inverse fourth-power and sixth-power, respectively. The rapid drop in power contained in the near-field ensures that effects due to the near-field essentially vanish a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kirchhoff's Diffraction Formula
Kirchhoff's diffraction formula (also Fresnel–Kirchhoff diffraction formula) can be used to model the propagation of light in a wide range of configurations, either analytically or using numerical modelling. It gives an expression for the wave disturbance when a monochromatic spherical wave is the incoming wave of a situation under consideration. This formula is derived by applying the Kirchhoff integral theorem, which uses the Green's second identity to derive the solution to the homogeneous scalar wave equation, to a spherical wave with some approximations. The Huygens–Fresnel principle is derived by the Fresnel-Kirchhoff diffraction formula. Derivation of Kirchhoff's diffraction formula Kirchhoff's integral theorem, sometimes referred to as the Fresnel–Kirchhoff integral theorem, uses Green's second identity to derive the solution of the homogeneous scalar wave equation at an arbitrary spatial position P in terms of the solution of the wave equation and its firs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Surface Equivalence Principle
In electromagnetism, surface equivalence principle or surface equivalence theorem relates an arbitrary current distribution within an imaginary closed surface with an equivalent source on the surface. It is also known as field equivalence principle, Huygens' equivalence principle or simply as the equivalence principle. Being a more rigorous reformulation of the Huygens–Fresnel principle, it is often used to simplify the analysis of radiating structures such as antennas. Certain formulations of the principle are also known as Love equivalence principle and Schelkunoff equivalence principle, after Augustus Edward Hough Love and Sergei Alexander Schelkunoff, respectively. Physical meaning General formulation The principle yields an equivalent problem for a radiation problem by introducing an imaginary closed surface and fictitious surface current densities. It is an extension of Huygens–Fresnel principle, which describes each point on a wavefront as a spherical wave source. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Antenna (radio)
In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an electric current to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic waves (radio waves). In reception, an antenna intercepts some of the power of a radio wave in order to produce an electric current at its terminals, that is applied to a receiver to be amplified. Antennas are essential components of all radio equipment. An antenna is an array of conductors ( elements), electrically connected to the receiver or transmitter. Antennas can be designed to transmit and receive radio waves in all horizontal directions equally ( omnidirectional antennas), or preferentially in a particular direction ( directional, or high-gain, or “beam” antennas). An antenna may include components not conn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corpuscular Theory
In optics, the corpuscular theory of light states that light is made up of small discrete particles called " corpuscles" (little particles) which travel in a straight line with a finite velocity and possess impetus. This was based on an alternate description of atomism of the time period. Isaac Newton laid the foundations for this theory through his work in optics. This early conception of the particle theory of light was an early forerunner to the modern understanding of the photon. This theory came to dominate the conceptions of light in the eighteenth century, displacing the previously prominent vibration theories, where light was viewed as 'pressure' of the medium between the source and the receiver, first championed by René Descartes, and later in a more refined form by Christiaan Huygens. It would fall out of the spotlight in the early nineteenth century, as the wave theory of light amassed new experimental evidence. Mechanical philosophy In the early 17th century, natu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arago Spot
Arago may refer to: People * Aragó, a family name of the kings of the Aragonese Crown * Étienne Arago (1802–1892), French journalist, theater director, and politician; brother of Juan, François, and Jacques * François Arago (1786–1853), French mathematician, physicist, astronomer, and politician; brother of Juan, Jacques, and Étienne * Jacques Arago (1790–1855), French writer, artist and explorer; brother of Juan, François, and Étienne * Josep Riera i Aragó (born 1954), Catalan artist * Marie Arago (1755–1845), French mother of the six Arago brothers Places Earth *Aragó, the name for Aragon in Catalan *Arago, Oregon, United States, an unincorporated community *Arago Township, Minnesota, United States *Cape Arago, Cape Arago State Park, Oregon, United States * Arago Glacier, Graham Land, Antarctica *Arago cave, Tautavel, France, a site where prehistoric remains of Tautavel Man were discovered * Arago hotspot, a geological hotspot near the Arago seamount in the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Principles Of Optics
''Principles of Optics'', colloquially known as ''Born and Wolf'', is an optics textbook written by Max Born and Emil Wolf that was initially published in 1959 by Pergamon Press. After going through six editions with Pergamon Press, the book was transferred to Cambridge University Press who issued an expanded seventh edition in 1999. A 60th anniversary edition was published in 2019 with a foreword by Sir Peter Knight. It is considered a classic science book and one of the most influential optics books of the twentieth century. Background In 1933, Springer published Max Born's book “Optik”; this dealt with all optical phenomena for which the methods of classical physics, and Maxwell's equations in particular, were applicable. In 1950, with encouragement from Sir Edward Appleton, the principal of Edinburgh University, Born decided to produce an updated version of his “Optik” book in English. He was partly motivated by the need to make money, as he had not been workin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
