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  • Radiation | Britannica.com
    He was a member of a scientific family extending through several generations Beer s law in spectroscopy a relation concerning the absorption of radiant energy by an absorbing medium Formulated by German mathematician and chemist August Beer in 1852 it states that the absorptive capacity of a dissolved substance is directly proportional bioluminescence emission of light by an organism or by a laboratory biochemical system derived from an organism It could be the ghostly glow of bacteria on decaying meat or fish the shimmering radiance of protozoans in tropical seas or the flickering signals of fireflies blackbody in physics a surface that absorbs all radiant energy falling on it The term arises because incident visible light will be absorbed rather than reflected and therefore the surface will appear black The concept of such a perfect absorber of energy Bothe Walther German physicist who shared the Nobel Prize for Physics in 1954 with Max Born for his invention of a new method of detecting subatomic particles and for other resulting discoveries Bothe taught at the universities of Berlin 1920 31 Giessen 1931 34 bremsstrahlung German braking radiation electromagnetic radiation produced by a sudden slowing down or deflection of charged particles especially electrons passing through matter in the vicinity of the strong electric fields of atomic nuclei Bremsstrahlung bubble chamber radiation detector that uses as the detecting medium a superheated liquid that boils into tiny bubbles of vapour around the ions produced along the tracks of subatomic particles The bubble chamber was developed in 1952 by the American physicist Donald carrier wave in electronics the unmodulated single frequency electromagnetic wave that carries the desired information i e is modulated by the information See modulation electronics cathode ray stream of electrons leaving the negative electrode cathode in a discharge tube containing a gas at low pressure or electrons emitted by a heated filament in certain electron tubes Cathode rays focused on a hard target anticathode produce X rays Charpak Georges Polish born French physicist winner of the Nobel Prize for Physics in 1992 for his invention of subatomic particle detectors in particular the multiwire proportional chamber Charpak s family moved from Poland to Paris when he was seven years old chemiluminescence emission of electromagnetic radiation during the course of chemical reactions Such radiation whether ultraviolet visible or infrared is most commonly generated by oxidation The radiation can usually be ascribed to the transfer of the oxidation Cherenkov radiation light produced by charged particles when they pass through an optically transparent medium at speeds greater than the speed of light in that medium Devices sensitive to this particular form of radiation called Cherenkov detectors have been used extensively chromophore a group of atoms and electrons forming part of an organic molecule that causes it to be coloured Correlations between the structural features of chemical compounds and their colours have been sought since about 1870 when it was noted that quinones cloud chamber radiation detector originally developed between 1896 and 1912 by the Scottish physicist

    Original URL path: http://www.britannica.com/topic-browse/Physics/Radiation (2016-02-13)
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  • Radioactivity | Britannica.com
    Curie Marie Polish born French physicist famous for her work on radioactivity and twice a winner of the Nobel Prize With Henri Becquerel and her husband Pierre Curie she was awarded the 1903 Nobel Prize for Physics She was the sole winner of the 1911 Nobel Curie Pierre French physical chemist cowinner of the Nobel Prize for Physics in 1903 He and his wife Marie Curie discovered radium and polonium in their investigation of radioactivity An exceptional physicist he was one of the main founders of modern physics decay constant proportionality between the size of a population of radioactive atoms and the rate at which the population decreases because of radioactive decay Suppose N is the size of a population of radioactive atoms at a given time t and d N is the amount by displacement law in physics any of the statements originally formulated in 1913 that radioactive decay produces daughter atoms whose position in the periodic table of the chemical elements is shifted from that of their parents two lower for alpha decay and one higher fallout deposition of radioactive materials on Earth from the atmosphere The terms rain out and snow out are sometimes used to specify such deposition during precipitant weather Radioactivity in the atmosphere may arise from 1 natural causes 2 nuclear Fermi Enrico Italian born American scientist who was one of the chief architects of the nuclear age He developed the mathematical statistics required to clarify a large class of subatomic phenomena explored nuclear transformations caused by neutrons and directed gamma decay type of radioactivity in which some unstable atomic nuclei dissipate excess energy by a spontaneous electromagnetic process In the most common form of gamma decay known as gamma emission gamma rays photons or packets of electromagnetic energy of Geiger Hans German physicist

    Original URL path: http://www.britannica.com/topic-browse/Physics/Radioactivity (2016-02-13)
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  • Relativity | Britannica.com
    force s in the universe Gravity defines Heckmann Otto German astronomer noted for his work in measuring stellar positions and for his studies of relativity and cosmology He also made notable contributions to statistical mechanics After obtaining his Ph D 1925 at the University of Bonn Heckmann became Levi Civita Tullio Italian mathematician known for his work in differential calculus and relativity theory At the University of Padua 1891 95 he studied under Gregorio Ricci Curbastro with whom he later collaborated in founding the absolute differential calculus now Minkowski Hermann German mathematician who developed the geometrical theory of numbers and who made numerous contributions to number theory mathematical physics and the theory of relativity His idea of combining the three dimensions of physical space with that of time Penrose Sir Roger British mathematician and relativist who in the 1960s calculated many of the basic features of black holes After obtaining a Ph D in algebraic geometry from the University of Cambridge in 1957 Penrose held temporary posts at a number of universities Poincaré Henri French mathematician one of the greatest mathematicians and mathematical physicists at the end of 19th century He made a series of profound innovations in geometry the theory of differential equations electromagnetism topology and the philosophy quantum field theory body of physical principles combining the elements of quantum mechanics with those of relativity to explain the behaviour of subatomic particles and their interactions via a variety of force fields Two examples of modern quantum field theories are quantum relativity wide ranging physical theories formed by the German born physicist Albert Einstein With his theories of special relativity 1905 and general relativity 1915 Einstein overthrew many assumptions underlying earlier physical theories redefining in Riemann Bernhard German mathematician whose profound and novel approaches to the study of geometry laid

    Original URL path: http://www.britannica.com/topic-browse/Physics/Relativity (2016-02-13)
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  • Subatomic Particles | Britannica.com
    273 15 C or 459 67 F K kelvin coalesce into a single quantum mechanical entity that is one that can be described by a wave function Bose Einstein statistics one of two possible ways in which a collection of indistinguishable particles may occupy a set of available discrete energy states The aggregation of particles in the same state which is characteristic of particles obeying Bose Einstein statistics boson subatomic particle with integral spin i e angular momentum in quantum mechanical units of 0 1 etc that is governed by the Bose Einstein statistics Bosons include mesons e g pions and kaons nuclei of even mass number e g helium 4 and Bothe Walther German physicist who shared the Nobel Prize for Physics in 1954 with Max Born for his invention of a new method of detecting subatomic particles and for other resulting discoveries Bothe taught at the universities of Berlin 1920 31 Giessen 1931 34 charge conjugation in particle physics an operation that replaces particles with antiparticles and vice versa in equations describing subatomic particles The name charge conjugation arises because a given particle and its antiparticle generally carry opposite electric charge conservation in physics constancy of the total electric charge in the universe or in any specific chemical or nuclear reaction The total charge in any closed system never changes at least within the limits of the most precise observation In classical terms this complementarity principle in physics tenet that a complete knowledge of phenomena on atomic dimensions requires a description of both wave and particle properties The principle was announced in 1928 by the Danish physicist Niels Bohr Depending on the experimental arrangement CP violation in particle physics violation of the combined conservation laws associated with charge conjugation C and parity P by the weak force which is responsible for reactions such as the radioactive decay of atomic nuclei Charge conjugation is a mathematical de Broglie wave any aspect of the behaviour or properties of a material object that varies in time or space in conformity with the mathematical equations that describe waves By analogy with the wave and particle behaviour of light that had already been established Eightfold Way classification of subatomic particles known as hadrons into groups on the basis of their symmetrical properties the number of members of each group being 1 8 most frequently 10 or 27 The system was proposed in 1961 by the American physicist Murray electron lightest stable subatomic particle known It carries a negative charge which is considered the basic unit of electric charge The rest mass of the electron is 9 109 10 31 kg which is only 1 1 840 the mass of a proton An electron is therefore considered electron beam stream of electrons as from a betatron generated by heat thermionic emission bombardment of charged atoms or particles secondary electron emission or strong electric fields field emission Electrons may be collimated by holes and slits and electron charge symbol e fundamental physical constant expressing the

    Original URL path: http://www.britannica.com/topic-browse/Physics/Subatomic-Particles (2016-02-13)
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  • Thermodynamics | Britannica.com
    science who emphasized a history of modern science based on evolutionary metaphysical concepts He maintained that the role of theory in science is to systematize relationships rather than to interpret Espy James Pollard American meteorologist who apparently gave the first essentially correct explanation of the thermodynamics of cloud formation and growth He was also one of the first to use the telegraph for collecting meteorological observations Espy served as a meteorologist Gibbs J Willard theoretical physicist and chemist who was one of the greatest scientists in the United States in the 19th century His application of thermodynamic theory converted a large part of physical chemistry from an empirical into a deductive science Gibbs heat energy that is transferred from one body to another as the result of a difference in temperature If two bodies at different temperatures are brought together energy is transferred i e heat flows from the hotter body to the colder The effect of this Lewis Gilbert N American physical chemist best known for his contributions to chemical thermodynamics the electron pair model of the covalent bond the electronic theory of acids and bases the separation and study of deuterium and its compounds and his work on phosphorescence Maxwell James Clerk Scottish physicist best known for his formulation of electromagnetic theory He is regarded by most modern physicists as the scientist of the 19th century who had the greatest influence on 20th century physics and he is ranked with Sir Isaac Newton Onsager Lars Norwegian born American chemist whose development of a general theory of irreversible chemical processes gained him the 1968 Nobel Prize for Chemistry His early work in statistical mechanics attracted the attention of the Dutch chemist Peter Debye Planck Max German theoretical physicist who originated quantum theory which won him the Nobel Prize for

    Original URL path: http://www.britannica.com/topic-browse/Physics/Thermodynamics (2016-02-13)
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  • Time | Britannica.com
    on January 1 1960 The unit of UTC is the atomic second and UTC is widely broadcast by radio signals These signals ultimately furnish the basis for the setting of all public day time required for a celestial body to turn once on its axis especially the period of the Earth s rotation The sidereal day is the time required for the Earth to rotate once relative to the background of the stars i e the time between two observed dynamical time specialized timescale used to describe the motion of objects in space As a practical matter time can be defined as that coordinate which can most simply be related to the evolution of closed systems Proper time is the time measured by a clock in a Ephemeris Time ET the first dynamical time scale in history it was defined by the International Astronomical Union in the 1950s and was superseded by Barycentric Dynamical Time in 1984 See dynamical time Ephemeris Time could be obtained by observing the orbital geologic time the extensive interval of time occupied by the geologic history of Earth It extends from about 4 6 billion years ago corresponding to Earth s initial formation to the present day It is in effect that segment of Earth history that is represented Greenwich Mean Time GMT the name for mean solar time of the longitude 0 of the Royal Greenwich Observatory in England The meridian at this longitude is called the prime meridian or Greenwich meridian Greenwich Mean Time was used for clearly designating epoch by avoiding hour in timekeeping 3 600 seconds now defined in terms of radiation emitted from atoms of the element cesium under specified conditions The hour was formerly defined as the 24th part of a mean solar day i e of the average period of rotation of the Metonic cycle in chronology a period of 19 years in which there are 235 lunations or synodic months after which the Moon s phases recur on the same days of the solar year or year of the seasons The cycle was discovered by Meton fl 432 bc an Athenian astronomer millennium a period of 1 000 years The Gregorian calendar put forth in 1582 and subsequently adopted by most countries did not include a year 0 in the transition from bc years before Christ to ad those since his birth Thus the 1st millennium is defined minute in timekeeping 60 seconds now defined in terms of radiation emitted from atoms of the element cesium under specified conditions The minute was formerly defined as the 60th part of an hour or the 1 440th part 60 24 hours 1 440 of a mean solar month a measure of time corresponding or nearly corresponding to the length of time required by the Moon to revolve once around the Earth The synodic month or complete cycle of phases of the Moon as seen from Earth averages 29 530588 mean solar days in National Institute of Standards and Technology

    Original URL path: http://www.britannica.com/topic-browse/Physics/Time (2016-02-13)
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  • Physics - 3 | Britannica.com
    atoms in crystalline solids and with the geometric structure of crystal lattices Classically the optical properties of crystals were of value in mineralogy and chemistry for Ctesibius of Alexandria Greek physicist and inventor the first great figure of the ancient engineering tradition of Alexandria Egypt Ctesibius was the son of a barber The discovery of the elasticity of air is attributed to Ctesibius as is the invention of several devices Curie Marie Polish born French physicist famous for her work on radioactivity and twice a winner of the Nobel Prize With Henri Becquerel and her husband Pierre Curie she was awarded the 1903 Nobel Prize for Physics She was the sole winner of the 1911 Nobel Curie Pierre French physical chemist cowinner of the Nobel Prize for Physics in 1903 He and his wife Marie Curie discovered radium and polonium in their investigation of radioactivity An exceptional physicist he was one of the main founders of modern physics Daguerre Louis Jacques Mandé French painter and physicist who invented the first practical process of photography known as the daguerreotype Though the first permanent photograph from nature was made in 1826 27 by Nicéphore Niépce of France it was of poor quality and required Dalén Nils Swedish engineer who won the Nobel Prize for Physics in 1912 for his invention of the automatic sun valve or Solventil which regulates a gaslight source by the action of sunlight turning it off at dawn and on at dusk or at other periods of darkness Dalton John English meteorologist and chemist a pioneer in the development of modern atomic theory Early life and education Dalton was born into a Quaker family of tradesmen his grandfather Jonathan Dalton was a shoemaker and his father Joseph was a weaver Davies Paul British theoretical physicist and astrobiologist who contributed to scholarly and popular debate on issues such as the origin of life and extraterrestrial intelligence through his books and television specials Davies graduated from University College Davis Raymond Jr American physicist who with Koshiba Masatoshi won the Nobel Prize for Physics in 2002 for detecting neutrino s Riccardo Giacconi also won a share of the award for his work on X rays Davis received a Ph D from Yale University in 1942 After military Davisson Clinton Joseph American experimental physicist who shared the Nobel Prize for Physics in 1937 with George P Thomson of England for discovering that electrons can be diffracted like light waves thus verifying the thesis of Louis de Broglie that electrons behave both Day Arthur L U S geophysicist known for his studies of the properties of rocks and minerals at very high and very low temperatures He investigated hot springs and earthquakes the absolute measurement of high temperatures and physical and chemical problems regarding decay constant proportionality between the size of a population of radioactive atoms and the rate at which the population decreases because of radioactive decay Suppose N is the size of a population of radioactive atoms at a given time t and d N is the amount by decibel dB unit for expressing the ratio between two amounts of electric or acoustic power or for measuring the relative loudness of sounds One decibel 0 1 bel equals 10 times the common logarithm of the power ratio i e doubling the intensity of a sound Dehmelt Hans Georg German born American physicist who shared one half of the Nobel Prize for Physics in 1989 with the German physicist Wolfgang Paul The other half of the prize was awarded to the American physicist Norman F Ramsey Dehmelt received his share of the Delaunay Charles Eugène French mathematician and astronomer whose theory of lunar motion advanced the development of planetary motion theories Delaunay was educated as an engineer at the École des Mines from 1836 becoming an engineer in 1843 and chief engineer in 1858 He Dempster Arthur Jeffrey American physicist who built the first mass spectrometer a device used to separate and measure the quantities of different charged particles such as atomic nuclei or molecular fragments Dempster was educated at the University of Toronto A B 1909 Deslandres Henri Alexandre French physicist and astrophysicist who in 1894 invented a spectroheliograph an instrument that photographs the Sun in monochromatic light About a year earlier George E Hale had independently invented a spectroheliograph in the United States After Dewar Sir James British chemist and physicist whose study of low temperature phenomena entailed the use of a double walled vacuum flask of his own design which has been named for him Educated at the University of Edinburgh Dewar became a professor at the University Dicke Robert H American physicist noted for his theoretical work in cosmology and investigations centring on the general theory of relativity He also made a number of significant contributions to radar technology and to the field of atomic physics Dicke received dielectric constant property of an electrical insulating material a dielectric equal to the ratio of the capacitance of a capacitor filled with the given material to the capacitance of an identical capacitor in a vacuum without the dielectric material The insertion of Dietz Robert S American geophysicist and oceanographer who set forth a theory of seafloor spreading in 1961 Dietz was educated at the University of Illinois B S 1937 M S 1939 Ph D 1941 After serving as an officer in the U S Army Air Corps during World diffraction grating component of optical devices consisting of a surface ruled with close equidistant and parallel lines for the purpose of resolving light into spectra A grating is said to be a transmission or reflection grating according to whether it is transparent diopter in optics unit of magnifying power of a lens or lens system Because the power of a lens is proportional to unity one divided by the focal length see lens the power of a lens in diopters is numerically equal to 1 m divided by the focal length in dip circle instrument for measuring the inclination or

    Original URL path: http://www.britannica.com/topic-browse/Physics/3 (2016-02-13)
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  • Physics - 4 | Britannica.com
    Jean French physicist who pioneered in optics and did much to establish the wave theory of light advanced by English physicist Thomas Young Beginning in 1804 Fresnel served as an engineer building roads in various departments of France He began his research Fresnel lens succession of concentric rings each consisting of an element of a simple lens assembled in proper relationship on a flat surface to provide a short focal length The Fresnel lens is used particularly in lighthouses and searchlights to concentrate the friction force that resists the sliding or rolling of one solid object over another Frictional forces such as the traction needed to walk without slipping may be beneficial but they also present a great measure of opposition to motion About 20 percent of Friedman Jerome Isaac American physicist who together with Richard E Taylor and Henry W Kendall received the Nobel Prize for Physics in 1990 for their joint experimental confirmation of the fundamental particles known as quarks Friedman was educated at the University Frisch Otto Robert physicist who with his aunt Lise Meitner described the division of neutron bombarded uranium into lighter elements and named the process fission 1939 At the time Meitner was working in Stockholm and Frisch at Copenhagen under Niels Bohr who brought Frisi Paolo Italian mathematician astronomer and physicist who is best known for his work in hydraulics His most significant contributions to science however were in the compilation interpretation and dissemination of the work of other scientists Frisi was Fuchs Klaus German born physicist and spy who was arrested and convicted 1950 for giving vital American and British atomic research secrets to the Soviet Union Fuchs studied physics and mathematics at the Universities of Leipzig and Kiel and joined the German Fuglesang Christer Swedish physicist and astronaut the first Swedish citizen in space Fuglesang earned a master s degree in engineering physics from the Royal Institute of Technology KTH in Stockholm in 1981 and received a doctorate in experimental particle physics Gabor Dennis Hungarian born electrical engineer who won the Nobel Prize for Physics in 1971 for his invention of holography a system of lensless three dimensional photography that has many applications A research engineer for the firm of Siemens and Halske in Galileo Italian natural philosopher astronomer and mathematician who made fundamental contributions to the sciences of motion astronomy and strength of materials and to the development of the scientific method His formulation of circular inertia the Galvani Luigi Italian physician and physicist who investigated the nature and effects of what he conceived to be electricity in animal tissue His discoveries led to the invention of the voltaic pile a kind of battery that makes possible a constant source of current gamma ray astronomy study of astronomical objects and phenomena that emit gamma ray s Gamma ray telescope s are designed to observe high energy astrophysical systems including stellar corona s white dwarf star s neutron star s black hole s supernova remnant s clusters Gamow George Russian born American nuclear physicist and cosmologist who was one of the foremost advocates of the big bang theory according to which the universe was formed in a colossal explosion that took place billions of years ago In addition his work on deoxyribonucleic gauge theory class of quantum field theory a mathematical theory involving both quantum mechanics and Einstein s special theory of relativity that is commonly used to describe subatomic particles and their associated wave fields In a gauge theory there is a group Gauss Carl Friedrich German mathematician generally regarded as one of the greatest mathematicians of all time for his contributions to number theory geometry probability theory geodesy planetary astronomy the theory of functions and potential theory including electromagnetism Gay Lussac Joseph Louis French chemist and physicist who pioneered investigations into the behaviour of gases established new techniques for analysis and made notable advances in applied chemistry Early career Gay Lussac was the eldest son of a provincial lawyer and royal Geiger Hans German physicist who introduced the first successful detector the Geiger counter of individual alpha particles and other ionizing radiations Geiger was awarded a Ph D by the University of Erlangen in 1906 and shortly thereafter joined the staff of Geim Sir Andre physicist who was awarded the 2010 Nobel Prize for Physics for his experiments with graphene He shared the prize with his colleague and former student Konstantin Novoselov Geim held dual citizenship in the Netherlands and Great Britain Geim received Gell Mann Murray American physicist winner of the Nobel Prize for Physics for 1969 for his work pertaining to the classification of subatomic particles and their interactions Having entered Yale University at age 15 Gell Mann received a B S in physics in 1948 and Gennes Pierre Gilles de French physicist who was awarded the 1991 Nobel Prize for Physics for his discoveries about the ordering of molecules in liquid crystals and polymers The son of a physician Gennes studied at the École Normale Supérieure He was employed as an engineer geomagnetic field magnetic field associated with the Earth It primarily is dipolar i e it has two poles these being the north and south magnetic poles on the Earth s surface Away from the surface the dipole becomes distorted In the 1830s the German mathematician geomagnetics branch of geophysics concerned with all aspects of the Earth s magnetic field including its origin variation through time and manifestations in the form of magnetic poles the remanent magnetization of rocks and local or regional magnetic anomalies Geophone trade name for an acoustic detector that responds to ground vibrations generated by seismic waves Geophones also called jugs pickups and tortugas are placed on the ground surface in various patterns or arrays to record the vibrations generated by geophysics major branch of the Earth sciences that applies the principles and methods of physics to the study of the Earth A brief treatment of geophysics follows For full treatment see geology Geophysics Geophysics deals with a wide array of

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