A beam of white light (entering upwards from the right) is dispersed into its constituent colors by its passage through a prism. In Optics, a dispersive prism is a type of optical prism, normally having the shape of a geometrical triangular prism. The fainter beam of white light exiting to the upper right has been reflected (without dispersion) off the first surface of the prism.

Light, or visible light, is electromagnetic radiation of a wavelength that is visible to the human eye (about 400–700 nm). Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Eyes are organs that detect Light, and send signals along the Optic nerve to the visual areas of the brain A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a In a scientific context, the word light is sometimes used to refer to the entire electromagnetic spectrum. Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Moreover, in optics, the term "visible light" refers to electromagnetic radiation with wavelengths of ~300 nm (near UV) through ~1400 nm (near infrared). Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of ^[1] Light is composed of elementary particles called photons. In Particle physics, an elementary particle or fundamental particle is a particle not known to have substructure that is it is not known to be made In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena

Three primary properties of light are:

• Intensity;
• Frequency or wavelength and;
• Polarization. In Physics, intensity is a measure of the time-averaged Energy Flux. Frequency is a measure of the number of occurrences of a repeating event per unit Time. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations

Light can exhibit properties of both waves and particles. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them This property is referred to as wave–particle duality. In Physics and Chemistry, wave–particle duality is the concept that all Matter and Energy exhibits both Wave -like and The study of light, known as optics, is an important research area in modern physics. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion.

Speed of light

Main article: Speed of light

A line showing the speed of light on a scale model of Earth and the moon, about 1. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 2 seconds.

The speed of light in a vacuum is exactly 299,792,458 m/s (about 186,282. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. 397 miles per second). The speed of light depends upon the medium in which it is traveling, and the speed will be lower in a transparent medium. Although commonly called the "velocity of light", technically the word velocity is a vector quantity, having both magnitude and direction. In Physics, velocity is defined as the rate of change of Position. Speed refers only to the magnitude of the velocity vector. This fixed definition of the speed of light is a result of the modern attempt, in physics, to define the basic unit of length in terms of the speed of light, rather than defining the speed of light in terms of a length. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International

Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher A good early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Ole Christensen Rømer (o(ːlə ˈʁœːˀmɐ in Danish 25 September 1644, Århus – 19 September 1710, Copenhagen) Using a telescope, Ole observed the motions of Jupiter and one of its moons, Io. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek Noting discrepancies in the apparent period of Io's orbit, Rømer calculated that light takes about 18 minutes to traverse the diameter of Earth's orbit. Unfortunately, this was not a value that was known at that time. If Ole had known the diameter of the earth's orbit, he would have calculated a speed of 227,000,000 m/s.

Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849. Armand Hippolyte Louis Fizeau (1819-1896 French physicist, was born in Paris. Year 1849 ( MDCCCXLIX) was a Common year starting on Monday (link will display the full calendar of the Gregorian calendar (or a Common Fizeau directed a beam of light at a mirror several kilometers away. A rotating cog wheel was placed in the path of the light beam as it traveled from the source, to the mirror and then returned to its origin. Fizeau found that at a certain rate of rotation, the beam would pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to calculate the speed of light as 313,000,000 m/s.

Léon Foucault used an experiment which used rotating mirrors to obtain a value of 298,000,000 m/s in 1862. Jean Bernard Léon Foucault (ʒɑ̃ bɛʁnaʁ leɔ̃ fu'ko ( 18 September 1819 &ndash 11 February 1868) was a French physicist Year 1862 was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common year starting on Monday Albert A. Michelson conducted experiments on the speed of light from 1877 until his death in 1931. Albert Abraham Michelson ( December 19, 1852 &ndash May 9, 1931) was a Polish - American Physicist known He refined Foucault's methods in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt. A mirror is an object with a surface that has good Specular reflection; that is it is smooth enough to form an Image. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Wilson to Mt. San Antonio in California. California ( is a US state on the West Coast of the United States, along the Pacific Ocean. The precise measurements yielded a speed of 299,796,000 m/s.

Some scientists were able to bring light to a complete standstill by passing it through a Bose-Einstein Condensate of the element rubidium. A Bose–Einstein condensate (BEC is a State of matter of Bosons confined in an external Potential and cooled to Temperatures very near to

Refraction

Note, n = 1 in a vacuum and n > 1 in a transparent medium, where n is the index of refraction. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium

When a beam of light crosses the boundary between a vacuum and another medium, or between two different mediums, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal to the boundary, the change in wavelength results in a change in the direction of the beam. In Mathematics, two Vectors are orthogonal if they are Perpendicular, i This change of direction is known as refraction.

The refraction quality of lenses is frequently used to manipulate light in order to change the apparent size of images. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging Magnifying glasses, spectacles, contact lenses, microscopes and refracting telescopes are all examples of this manipulation. magnifying glass (called a hand lens in laboratory contexts is a convex lens which is used to produce a magnified Image of an object Glasses, also called eyeglasses or spectacles, are frames bearing lenses worn in front of the Eyes normally for vision correction, A contact lens (also known simply as a contact) is a corrective, cosmetic, or therapeutic lens usually placed on the Cornea A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are A refracting or refractor telescope is a dioptric Telescope that uses a lens as its objective to form an image

Optics

Main article: Optics

The study of light and the interaction of light and matter is termed optics. Matter is commonly defined as being anything that has mass and that takes up space. The observation and study of optical phenomena such as rainbows and the aurora borealis offer many clues as to the nature of light as well as much enjoyment. An optical phenomenon is any observable event which results from the interaction of Light and Matter. A rainbow is an optical and meteorological phenomenon that causes a spectrum of Light to appear in the Sky when the Sun

Light sources

See also: List of light sources

A cloud illuminated by sunlight

There are many sources of light. This is a list of sources of Light, including both natural and artificial sources and both processes and devices. A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. This is a list of sources of Light, including both natural and artificial sources and both processes and devices. The most common light sources are thermal: a body at a given temperature emits a characteristic spectrum of black-body radiation. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature In Physics, a black body is an object that absorbs all light that falls on it Examples include sunlight (the radiation emitted by the chromosphere of the Sun at around 6,000 K peaks in the visible region of the electromagnetic spectrum), incandescent light bulbs (which emit only around 10% of their energy as visible light and the remainder as infrared), and glowing solid particles in flames. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. The chromosphere (literally "colour sphere" is a thin layer of the Sun 's atmosphere just above the Photosphere, roughly 10000 kilometres deep The Sun (Sol is the Star at the center of the Solar System. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The incandescent light bulb, incandescent lamp or incandescent light globe is a source of electric Light that works by Incandescence, (a general Fire is the heat and light energy released during a Chemical reaction, in particular a combustion reaction. The peak of the blackbody spectrum is in the infrared for relatively cool objects like human beings. As the temperature increases, the peak shifts to shorter wavelengths, producing first a red glow, then a white one, and finally a blue color as the peak moves out of the visible part of the spectrum and into the ultraviolet. These colors can be seen when metal is heated to "red hot" or "white hot". In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature The blue color is most commonly seen in a gas flame or a welder's torch. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane,

Atoms emit and absorb light at characteristic energies. This produces "emission lines" in the spectrum of each atom. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc. In Physics, emission is the process by which the Energy of a Photon is released by another entity for example by an Atom whose Electrons Spontaneous emission is the process by which a light source such as an Atom, Molecule, Nanocrystal or nucleus in an Excited state Gas discharge lamps are a family of artificial light sources that generate light by sending an Electrical discharge through an ionized gas i A neon lamp is a Gas discharge Lamp containing primarily Neon gas at low Pressure. Neon signs are luminous-tube signs that contain neon or other inert gases at a low pressure ), and flames (light from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow light). Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Emission can also be stimulated, as in a laser or a microwave maser. In Optics, stimulated emission is the process by which an electron perturbed by a Photon having the correct energy may drop to a lower Energy level resulting A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. A maser is a device that produces coherent Electromagnetic waves through amplification due to Stimulated emission.

Acceleration of a free charged particle, such as an electron, can produce visible radiation: cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Cyclotron radiation is Electromagnetic radiation emitted by moving charged particles deflected by a Magnetic field. This article concerns the physical phenomenon of synchrotron radiation Bremsstrahlung ( pronounced, from German de ''bremsen'' "to brake" and de ''Strahlung'' "radiation" i Particles moving through a medium faster than the speed of light in that medium can produce visible Cherenkov radiation. Čerenkov radiation (also spelled Cerenkov or Cherenkov) is Electromagnetic radiation emitted when a charged particle (such as an

Certain chemicals produce visible radiation by chemoluminescence. Chemiluminescence (sometimes " chemoluminescence " is the emission of Light ( Luminescence) with limited emission of heat as the result of a chemical In living things, this process is called bioluminescence. Bioluminescence' is the production and emission of Light by a living Organism as the result of a chemical reaction during which chemical energy is converted For example, fireflies produce light by this means, and boats moving through water can disturb plankton which produce a glowing wake. FireFly is the second single by Essex Alternative rock band InMe.

Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. Fluorescence is a Luminescence that is mostly found as an This is used in fluorescent lights. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence. Phosphorescence is a specific type of Photoluminescence related to fluorescence.

Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example of this. Cathodoluminescence is an optical and electrical Phenomenon whereby a beam of Electrons is generated by an Electron gun (e This mechanism is used in cathode ray tube televisions. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic

Certain other mechanisms can produce light:

• scintillation
• electroluminescence
• sonoluminescence
• triboluminescence
• Cherenkov radiation

When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include:

• radioactive decay
• particle–antiparticle annihilation

Theories about light

Indian theories

In ancient India, the philosophical schools of Samkhya and Vaisheshika, from around the 6th–5th century BC, developed theories on light. Scintillation is a flash of Light produced in a transparent material by an Ionization event Electroluminescence (EL is an Optical phenomenon and Electrical phenomenon in which a material emits light in response to an Electric current passed through Sonoluminescence is the emission of short bursts of Light from imploding bubbles in a Liquid when excited by Sound. Triboluminescence is an Optical phenomenon in which Light is generated via the breaking of asymmetrical bonds in a Crystal when that material is scratched Čerenkov radiation (also spelled Cerenkov or Cherenkov) is Electromagnetic radiation emitted when a charged particle (such as an Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. to most kinds of particles, there is an associated antiparticle with the same Mass and opposite Electric charge. Sankhya, also Samkhya, ( सांख्य, IAST: sānkhya - 'enumeration' is one of the six schools of classical Indian philosophy. Vaisheshika, or Vaiśeṣika, (Sanskrit वैशॆषिक) is one of the six Hindu schools of Philosophy (orthodox Vedic systems The 6th century BC started the first day of 600 BC and ended the last day of 501 BC. The 5th century BC started the first day of 500 BC and ended the last day of 401 BC. According to the Samkhya school, light is one of the five fundamental "subtle" elements (tanmatra) out of which emerge the gross elements. The atomicity of these elements is not specifically mentioned and it appears that they were actually taken to be continuous. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in

On the other hand, the Vaisheshika school gives an atomic theory of the physical world on the non-atomic ground of ether, space and time. This article focuses on the historical models of the atom For a history of the study of how atoms combine to form molecules see History of the molecule. According to ancient and medieval science, aether (Greek grc αἰθήρ aithēr) also spelled æther or ether, is the material that fills (See Indian atomism. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in ) The basic atoms are those of earth (prthivı), water (apas), fire (tejas), and air (vayu), that should not be confused with the ordinary meaning of these terms. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny These atoms are taken to form binary molecules that combine further to form larger molecules. Motion is defined in terms of the movement of the physical atoms and it appears that it is taken to be non-instantaneous. Light rays are taken to be a stream of high velocity of tejas (fire) atoms. The particles of light can exhibit different characteristics depending on the speed and the arrangements of the tejas atoms. Around the first century BC, the Vishnu Purana correctly refers to sunlight as the "the seven rays of the sun". Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun.

Later in 499, Aryabhata, who proposed a heliocentric solar system of gravitation in his Aryabhatiya, wrote that the planets and the Moon do not have their own light but reflect the light of the Sun. Events By place Asia Kavadh I of Persia deposes his brother Djamasp and restores himself as king of Persia. Āryabhaṭa ( Devanāgarī: आर्यभट (AD 476 &ndash 550 is the first in the line of great mathematician-astronomers from the classical age of Indian mathematics In Astronomy, heliocentrism is the theory that the Sun is at the center of the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Gravitation is a natural Phenomenon by which objects with Mass attract one another Āryabhatīya, an astronomical treatise is the Magnum opus and only extant work of the 5th century Indian mathematician Aryabhata. The Sun (Sol is the Star at the center of the Solar System.

The Indian Buddhists, such as Dignāga in the 5th century and Dharmakirti in the 7th century, developed a type of atomism that is a philosophy about reality being composed of atomic entities that are momentary flashes of light or energy. Buddhism is a family of beliefs and practices Dignāga ( fl 5th century) was an Indian scholar and one of the Buddhist founders of Indian logic. The 5th century is the period from 401 to 500 in accordance with the Julian calendar in Anno Domini / Common Era. Dharmakirti ( ca 7th century was an Indian scholar and one of the Buddhist founders of Indian philosophical logic. The 7th century is the period from 601 to 700 in accordance with the Julian calendar in the Christian / Common Era. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in They viewed light as being an atomic entity equivalent to energy, similar to the modern concept of photons, though they also viewed all matter as being composed of these light/energy particles. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena

Greek and Hellenistic theories

Main article: Emission theory (vision)

In the fifth century BC, Empedocles postulated that everything was composed of four elements; fire, air, earth and water. Emission theory or extramission theory is the proposal that Visual perception is accomplished by rays of Light emitted by the Eyes This Empedocles ( Greek:, ca 490–430 BC was a Greek Pre-Socratic Philosopher and a citizen of Agrigentum, a Greek colony in Many ancient philosophies used a set of archetypal classical "elements" to explain patterns in Nature. He believed that Aphrodite made the human eye out of the four elements and that she lit the fire in the eye which shone out from the eye making sight possible. If this were true, then one could see during the night just as well as during the day, so Empedocles postulated an interaction between rays from the eyes and rays from a source such as the sun.

In about 300 BC, Euclid wrote Optica, in which he studied the properties of light. Euclid ( Greek:.) fl 300 BC also known as Euclid of Alexandria, is often referred to as the Father of Geometry Euclid postulated that light travelled in straight lines and he described the laws of reflection and studied them mathematically. He questioned that sight is the result of a beam from the eye, for he asks how one sees the stars immediately, if one closes one's eyes, then opens them at night. Of course if the beam from the eye travels infinitely fast this is not a problem.

In 55 BC, Lucretius, a Roman who carried on the ideas of earlier Greek atomists, wrote:

"The light & heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove. Year 55 BC was a year of the pre-Julian calendar. Events By place Rome Consuls Marcus Licinius Crassus and Titus Lucretius Carus (ca 99 BC- ca 55 BC was a Roman Poet and Philosopher. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in " - On the nature of the Universe

Despite being similar to later particle theories, Lucretius's views were not generally accepted and light was still theorized as emanating from the eye.

Ptolemy (c. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca 2nd century) wrote about the refraction of light, and developed a theory of vision that objects are seen by rays of light emanating from the eyes. The 2nd century is the period from 101 to 200 in accordance with the Julian calendar in the Christian / Common Era. Refraction is the change in direction of a Wave due to a change in its Speed.

Optical theory

Main article: Book of Optics

The Muslim scientist Ibn al-Haytham (c. The Book of Optics ( Arabic: Kitab al-Manazir, Latin: De Aspectibus or Opticae Thesaurus Alhazeni TemplateInfobox Muslim scholars --> ( Arabic: ابو علی، حسن بن حسن بن هيثم Latinized 965-1040), known as Alhacen in the West, in his Book of Optics, developed a broad theory that explained vision, using geometry and anatomy, which stated that each point on an illuminated area or object radiates light rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. 965 was a year in the 10th century. Events By Place Europe The Khazar fortress of Sarkel falls The Book of Optics ( Arabic: Kitab al-Manazir, Latin: De Aspectibus or Opticae Thesaurus Alhazeni In Psychology, visual perception is the ability to interpret information from Visible light reaching the Eyes The resulting Perception is also Geometry ( Greek γεωμετρία; geo = earth metria = measure is a part of Mathematics concerned with questions of size shape and relative position Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration The other rays strike at different angles and are not seen. He described the pinhole camera and invented the camera obscura, which produces an inverted image, and used it as an example to support his argument. A' pinhole camera' is a very simple Camera with no lens and a single very small Aperture. The camera obscura (Latin dark chamber) is an optical device used for example in drawing or for entertainment ^[1] This contradicted Ptolemy's theory of vision that objects are seen by rays of light emanating from the eyes. Alhacen held light rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy's theory of the refraction of light, and went on to discover the laws of refraction. Claudius Ptolemaeus ( Greek: Klaúdios Ptolemaîos; after 83 &ndash ca

He also carried out the first experiments on the dispersion of light into its constituent colors. His major work Kitab al-Manazir was translated into Latin in the Middle Ages, as well his book dealing with the colors of sunset. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. He dealt at length with the theory of various physical phenomena like shadows, eclipses, the rainbow. He also attempted to explain binocular vision, and gave a correct explanation of the apparent increase in size of the sun and the moon when near the horizon. Because of his extensive research on optics, Al-Haytham is considered the father of modern optics.

Al-Haytham also correctly argued that we see objects because the sun's rays of light, which he believed to be streams of tiny particles travelling in straight lines, are reflected from objects into our eyes. He understood that light must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration.

The 'plenum'

René Descartes (1596-1650) held that light was a disturbance of the plenum, the continuous substance of which the universe was composed. In 1637 he published a theory of the refraction of light that assumed, incorrectly, that light travelled faster in a denser medium than in a less dense medium. Refraction is the change in direction of a Wave due to a change in its Speed. Descartes arrived at this conclusion by analogy with the behaviour of sound waves. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Although Descartes was incorrect about the relative speeds, he was correct in assuming that light behaved like a wave and in concluding that refraction could be explained by the speed of light in different media. As a result, Descartes' theory is often regarded as the forerunner of the wave theory of light.

Particle theory

Pierre Gassendi (1592-1655), an atomist, proposed a particle theory of light which was published posthumously in the 1660s. Pierre Gassendi ( January 22, 1592 &ndash October 24, 1655) was a French Philosopher, priest, Scientist Isaac Newton studied Gassendi's work at an early age, and preferred his view to Descartes' theory of the plenum. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements He stated in his Hypothesis of Light of 1675 that light was composed of corpuscles (particles of matter) which were emitted in all directions from a source. One of Newton's arguments against the wave nature of light was that waves were known to bend around obstacles, while light travelled only in straight lines. He did, however, explain the phenomenon of the diffraction of light (which had been observed by Francesco Grimaldi) by allowing that a light particle could create a localised wave in the aether. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle Francesco Maria Grimaldi ( April 2, 1618 - December 28, 1663) was an Italian Mathematician and Physicist who According to ancient and medieval science, aether (Greek grc αἰθήρ aithēr) also spelled æther or ether, is the material that fills

Newton's theory could be used to predict the reflection of light, but could only explain refraction by incorrectly assuming that light accelerated upon entering a denser medium because the gravitational pull was greater. Reflection is the change in direction of a Wave front at an interface between two different media so that the wave front returns into the medium from which Refraction is the change in direction of a Wave due to a change in its Speed. An optical medium is material through which Electromagnetic waves propagate Gravitation is a natural Phenomenon by which objects with Mass attract one another Newton published the final version of his theory in his Opticks of 1704. Opticks is a book written by English physicist Isaac Newton that was released to the public in 1704. Year 1704 ( MDCCIV) was a Leap year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a His reputation helped the particle theory of light to hold sway during the 18th century. In Physics and Chemistry, wave–particle duality is the concept that all Matter and Energy exhibits both Wave -like and The 18th century lasted from 1701 to 1800 in the Gregorian calendar, in accordance with the Anno Domini / Common Era numbering system The particle theory of light led Laplace to argue that a body could be so massive that light could not escape from it. In other words it would become what is now called a black hole. Laplace withdrew his suggestion when the wave theory of light was firmly established. A translation of his essay appears in The large scale structure of space-time, by Stephen Hawking and George F. R. Ellis. Stephen William Hawking CH, CBE, FRS, FRSA (born 8 January 1942 is a British theoretical physicist. George F R Ellis, FRS, (born August 11, 1939) is the Distinguished Professor of Complex Systems in the Department of Mathematics and Applied

Wave theory

In the 1660s, Robert Hooke published a wave theory of light. Robert Hooke, FRS (18 July 1635 – 3 March 1703 was an English Natural philosopher and Polymath who played an important role in the A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. Christiaan Huygens worked out his own wave theory of light in 1678, and published it in his Treatise on light in 1690. Christiaan Huygens (ˈhaɪgənz in English ˈhœyɣəns in Dutch) ( April 14, 1629 &ndash July 8, 1695) was a Dutch He proposed that light was emitted in all directions as a series of waves in a medium called the Luminiferous ether. In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium.

Thomas Young's sketch of the two-slit experiment showing the diffraction of light. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle Young's experiments supported the theory that light consists of waves.

The wave theory predicted that light waves could interfere with each other like sound waves (as noted around 1800 by Thomas Young), and that light could be polarized. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Year -of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, but 12 days ahead since Saturday. Thomas Young (13 June 1773 &ndash 10 May 1829 was an English Polymath who contributed to the scientific understanding of vision, Light Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colors were caused by different wavelengths of light, and explained color vision in terms of three-colored receptors in the eye. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency.

Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory. Year 1746 ( MDCCXLVI) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle

Later, Augustin-Jean Fresnel independently worked out his own wave theory of light, and presented it to the Académie des Sciences in 1817. The French Academy of Sciences ( French: Académie des sciences) is a Learned society, founded in 1666 by Louis XIV at the Year 1817 ( MDCCCXVII) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common Simeon Denis Poisson added to Fresnel's mathematical work to produce a convincing argument in favour of the wave theory, helping to overturn Newton's corpuscular theory. Siméon-Denis Poisson (21 June 1781 &ndash 25 April 1840 was a French Mathematician, Geometer, and Physicist.

The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt in the late nineteenth century by the Michelson-Morley experiment. In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation The Michelson–Morley experiment, one of the most important and famous experiments in the History of physics, was performed in 1887 by Albert Michelson and

Newton's corpuscular theory implied that light would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Léon Foucault, in 1850. Jean Bernard Léon Foucault (ʒɑ̃ bɛʁnaʁ leɔ̃ fu'ko ( 18 September 1819 &ndash 11 February 1868) was a French physicist For the game see 1850 (board game. 1850 ( MDCCCL) was a Common year starting on Tuesday (link His result supported the wave theory, and the classical particle theory was finally abandoned.

Electromagnetic theory

A linearly-polarized light wave frozen in time and showing the two oscillating components of light; an electric field and a magnetic field perpendicular to each other and to the direction of motion (a transverse wave). Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A transverse wave is a moving Wave that consists of oscillations occurring perpendicular to the direction of energy transfer

In 1845, Michael Faraday discovered that the angle of polarization of a beam of light as it passed through a polarizing material could be altered by a magnetic field, an effect now known as Faraday rotation. Year 1845 ( MDCCCXLV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. In Physics, the Faraday effect or Faraday rotation is a Magneto-optical phenomenon or an interaction between Light and a Magnetic This was the first evidence that light was related to electromagnetism. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether.

Faraday's work inspired James Clerk Maxwell to study electromagnetic radiation and light. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation: he first stated this result in 1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism, which contained a full mathematical description of the behaviour of electric and magnetic fields, still known as Maxwell's equations. Year 1873 ( MDCCCLXXIII) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Common A Treatise on Electricity and Magnetism is an 1873 Textbook on Electromagnetism written by James Clerk Maxwell. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric Soon after, Heinrich Hertz confirmed Maxwell's theory experimentally by generating and detecting radio waves in the laboratory, and demonstrating that these waves behaved exactly like visible light, exhibiting properties such as reflection, refraction, diffraction, and interference. Heinrich Rudolf Hertz ( February 22, 1857 – January 1, 1894) was a German physicist who clarified and expanded the electromagnetic theory Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Maxwell's theory and Hertz's experiments led directly to the development of modern radio, radar, television, electromagnetic imaging, and wireless communications.

The special theory of relativity

The wave theory was wildly successful in explaining nearly all optical and electromagnetic phenomena, and was a great triumph of nineteenth century physics. By the late nineteenth century, however, a handful of experimental anomalies remained that could not be explained by or were in direct conflict with the wave theory. One of these anomalies involved a controversy over the speed of light. The constant speed of light predicted by Maxwell's equations and confirmed by the Michelson-Morley experiment contradicted the mechanical laws of motion that had been unchallenged since the time of Galileo, which stated that all speeds were relative to the speed of the observer. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher In 1905, Albert Einstein resolved this paradox by revising the Galilean model of space and time to account for the constancy of the speed of light. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Einstein formulated his ideas in his special theory of relativity, which radically altered humankind's understanding of space and time. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of Einstein also demonstrated a previously unknown fundamental equivalence between energy and mass with his famous equation

where E is energy, m is rest mass, and c is the speed of light. In Physics, mass–energy equivalence is the concept that for particles slower than light any Mass has an associated Energy and vice versa. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object

Particle theory revisited

Another experimental anomaly was the photoelectric effect, by which light striking a metal surface ejected electrons from the surface, causing an electric current to flow across an applied voltage. Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical Experimental measurements demonstrated that the energy of individual ejected electrons was proportional to the frequency, rather than the intensity, of the light. Frequency is a measure of the number of occurrences of a repeating event per unit Time. In Physics, intensity is a measure of the time-averaged Energy Flux. Furthermore, below a certain minimum frequency, which depended on the particular metal, no current would flow regardless of the intensity. These observations clearly contradicted the wave theory, and for years physicists tried in vain to find an explanation. In 1905, Einstein solved this puzzle as well, this time by resurrecting the particle theory of light to explain the observed effect. Because of the preponderance of evidence in favor of the wave theory, however, Einstein's ideas were met initially by great skepticism among established physicists. But eventually Einstein's explanation of the photoelectric effect would triumph, and it ultimately formed the basis for wave–particle duality and much of quantum mechanics. In Physics and Chemistry, wave–particle duality is the concept that all Matter and Energy exhibits both Wave -like and Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons

Quantum theory

A third anomaly that arose in the late 19th century involved a contradiction between the wave theory of light and measurements of the electromagnetic spectrum emitted by thermal radiators, or so-called black bodies. In Physics, a black body is an object that absorbs all light that falls on it Physicists struggled with this problem, which later became known as the ultraviolet catastrophe, unsuccessfully for many years. The ultraviolet catastrophe, also called the Rayleigh-Jeans catastrophe was a prediction of early 20th century Classical physics that an ideal Black body at In 1900, Max Planck developed a new theory of black-body radiation that explained the observed spectrum correctly. For a general introduction see Black body. In Physics, Planck's law describes the spectral radiance of Electromagnetic radiation Planck's theory was based on the idea that black bodies emit light (and other electromagnetic radiation) only as discrete bundles or packets of energy. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός These packets were called quanta, and the particle of light was given the name photon, to correspond with other particles being described around this time, such as the electron and proton. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive A photon has an energy, E, proportional to its frequency, f, by

where h is Planck's constant, λ is the wavelength and c is the speed of light. The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. Likewise, the momentum p of a photon is also proportional to its frequency and inversely proportional to its wavelength:

As it originally stood, this theory did not explain the simultaneous wave- and particle-like natures of light, though Planck would later work on theories that did. In 1918, Planck received the Nobel Prize in Physics for his part in the founding of quantum theory. The Nobel Prize in Physics (Nobelpriset i fysik is awarded once a year by the Royal Swedish Academy of Sciences.

Wave–particle duality

The modern theory that explains the nature of light includes the notion of wave–particle duality, described by Albert Einstein in the early 1900s, based on his study of the photoelectric effect and Planck's results. In Physics and Chemistry, wave–particle duality is the concept that all Matter and Energy exhibits both Wave -like and Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Introduction When a Metallic surface is exposed to Electromagnetic radiation above a certain threshold Frequency, the light is absorbed and Electrons Einstein asserted that the energy of a photon is proportional to its frequency. Frequency is a measure of the number of occurrences of a repeating event per unit Time. More generally, the theory states that everything has both a particle nature and a wave nature, and various experiments can be done to bring out one or the other. The particle nature is more easily discerned if an object has a large mass, and it was not until a bold proposition by Louis de Broglie in 1924 that the scientific community realized that electrons also exhibited wave–particle duality. Louis-Victor-Pierre-Raymond 7th duc de Broglie, FRS (də bʁœj ( August 15 1892 &ndash March 19 1987) was a French The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The wave nature of electrons was experimentally demonstrated by Davission and Germer in 1927. Einstein received the Nobel Prize in 1921 for his work with the wave–particle duality on photons (especially explaining the photoelectric effect thereby), and de Broglie followed in 1929 for his extension to other particles.

Quantum electrodynamics

The quantum mechanical theory of light and electromagnetic radiation continued to evolve through the 1920's and 1930's, and culminated with the development during the 1940's of the theory of quantum electrodynamics, or QED. Quantum electrodynamics ( QED) is a relativistic Quantum field theory of Electrodynamics. This so-called quantum field theory is among the most comprehensive and experimentally successful theories ever formulated to explain a set of natural phenomena. In quantum field theory (QFT the forces between particles are mediated by other particles QED was developed primarily by physicists Richard Feynman, Freeman Dyson, Julian Schwinger, and Shin-Ichiro Tomonaga. Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum Freeman John Dyson FRS (born December 15, 1923) is an English-born American theoretical Physicist and Mathematician, famous for his Julian Seymour Schwinger ( February 12, 1918 &ndash July 16, 1994) was an American Theoretical physicist. Sin-Itiro Tomonaga or Shinichirō Tomonaga (朝永 振一郎 Tomonaga Shin'ichirō, March 31, 1906 Feynman, Schwinger, and Tomonaga shared the 1965 Nobel Prize in Physics for their contributions.

Light pressure

Main article: Radiation pressure

Light pushes on objects in its way, just as the wind would do. Radiation pressure is the Pressure exerted upon any surface exposed to Electromagnetic radiation. This pressure is most easily explainable in particle theory: photons hit and transfer their momentum. Light pressure can cause asteroids to spin faster,^[2] acting on their irregular shapes as on the vanes of a windmill. Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but A windmill is a machine that is powered by the energy of the wind The possibility to make solar sails that would accelerate spaceships in space is also under investigation^[3][4]. Solar sails (also called light sails or photon sails, especially when they use Light sources other than the Sun) are a proposed form of

Although the motion of the Crookes radiometer was originally attributed to light pressure, this interpretation is incorrect; the characteristic Crookes rotation is the result of a partial vacuum. The Crookes radiometer, also known as the light mill, consists of an airtight glass bulb containing a partial Vacuum. ^[5] This should not be confused with the Nichols radiometer, in which the motion is directly caused by light pressure. A Nichols radiometer is the apparatus used by Ernest Fox Nichols and Gordon Ferrie Hull in 1901 for the measurement of Radiation pressure. ^[6]

Spirituality

Light Decoration for the feast of St. Thomas at Kallara Pazhayapalli in Kottayam, Kerala-Importance of light in religion

The sensory perception of light plays a central role in spirituality (vision, enlightenment, darshan, Tabor Light), and the presence of light as opposed to its absence (darkness) is a common Western metaphor of good and evil, knowledge and ignorance, and similar concepts. In Spirituality including Religion, visions comprise Inspirational renderings generally of a Future state and/or of a mythical Darśana ( Darshan, दर्शन is a Sanskrit term meaning "sight" (in the sense of an instance of seeing or beholding from a root In Eastern Orthodox theology, the Tabor Light (also Light of Tabor, Tabor's Light, Taboric Light; Greek: Φῶς του Θαβώρ In Religion, Ethics, and Philosophy, the phrase good and evil refers to the location of objects desires and Behaviors on a two-way Knowledge is defined ( Oxford English Dictionary) variously as (i expertise and skills acquired by a person through experience or education the theoretical or practical understanding

References

See also

External links