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Fizeau
Armand Hippolyte Louis Fizeau (; 23 September 1819 – 18 September 1896) was a French physicist who, in 1849, measured the speed of light to within 5% accuracy. In 1851, he measured the speed of light in moving water in an experiment known as the Fizeau experiment. Biography Fizeau was born in Paris to Louis and Beatrice Fizeau. He married into the de Jussieu botanical family. His earliest work was concerned with improvements in photographic processes. Following suggestions by François Arago, Léon Foucault and Fizeau collaborated in a series of investigations on the interference of light and heat. In 1848, he predicted the redshifting of electromagnetic waves. In 1849, Fizeau calculated a value for the speed of light to a better precision than the previous value determined by Ole Rømer in 1676. He used a beam of light reflected from a mirror 8633 meters away. The beam passed through the gaps between the teeth of a rapidly rotating wheel with 720 teeth. The speed o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fizeau Experiment
The Fizeau experiment was carried out by Hippolyte Fizeau in 1851 to measure the relative speeds of light in moving water. Fizeau used a special interferometer arrangement to measure the effect of movement of a medium upon the speed of light. According to the theories prevailing at the time, light traveling through a moving medium would be dragged along by the medium, so that the measured speed of the light would be a simple sum of its speed ''through'' the medium plus the speed ''of'' the medium. Fizeau indeed detected a dragging effect, but the magnitude of the effect that he observed was far lower than expected. When he repeated the experiment with air in place of water he observed no effect. His results seemingly supported the partial aether-drag hypothesis of Augustin-Jean Fresnel, a situation that was disconcerting to most physicists. Over half a century passed before a satisfactory explanation of Fizeau's unexpected measurement was developed with the advent of Albert Ein ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fizeau's Measurement Of The Speed Of Light In Air
From 1848 to 1849, Hippolyte Fizeau used a toothed wheel apparatus to perform absolute measurements of the speed of light in air. Subsequent experiments performed by Marie Alfred Cornu from 1872 to 1876 improved the methodology and made more accurate measurements. Fizeau's determination of the speed of light In 1848–49, Hippolyte Fizeau determined the speed of light using an intense light source at the bell tower of his father's holiday home in Suresnes, and a mirror 8,633 meters away on Montmartre. The light source was interrupted by a rotating cogwheel with 720 notches that could be rotated at a variable speed several times a second. (Figure 1) Fizeau increased the rotation speed of the cogwheel until light passing through one notch of the cogwheel would be completely eclipsed by the adjacent tooth. At 12.6 rotations per second, the light was eclipsed. At twice this speed (25.2 rotations per second), it was again visible as it passed through the next notch. At 3 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Foucault's Measurements Of The Speed Of Light
In 1850, Léon Foucault used a rotating mirror to perform a differential measurement of the speed of light in water versus its speed in air. In 1862, he used a similar apparatus to measure the speed of light in the air. Background In 1834, Charles Wheatstone developed a method of using a rapidly rotating mirror to study transient phenomena, and applied this method to measure the velocity of electricity in a wire and the duration of an electric spark. He communicated to François Arago the idea that his method could be adapted to a study of the speed of light. The early-to-mid 1800s were a period of intense debate on the particle-versus-wave nature of light. Although the observation of the Arago spot in 1819 may have seemed to settle the matter definitively in favor of Fresnel's wave theory of light, various concerns continued to appear to be addressed more satisfactorily by Newton's corpuscular theory. Arago expanded upon Wheatstone's concept in an 1838 publication, suggesting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Speed Of Light
The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time interval of second. The speed of light is invariant (physics), the same for all observers, no matter their relative velocity. It is the upper limit for the speed at which Information#Physics_and_determinacy, information, matter, or energy can travel through Space#Relativity, space. All forms of electromagnetic radiation, including visible light, travel at the speed of light. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and sensitive measurements, their finite speed has noticeable effects. Much starlight viewed on Earth is from the distant past, allowing humans to study the history of the universe by viewing distant objects. When Data communication, comm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fizeau (crater)
Fizeau is a prominent lunar impact crater that is located on the far side of the Moon, in the southern hemisphere. Nearby craters of note include Minkowski to the west-northwest, and Eijkman to the southwest. The inner wall of the crater rim is multiply terrace Terrace may refer to: Landforms and construction * Fluvial terrace, a natural, flat surface that borders and lies above the floodplain of a stream or river * Terrace, a street suffix * Terrace, the portion of a lot between the public sidewalk a ...d in the northern half, while the southern rim has a shear inner surface leading down to slumped deposits on the crater floor. There is a small but prominent crater lying across the southwest rim, with an inner surface that forms terraced steps covering most of the interior. There are also smaller craterlets on the rim to the northeast and west-southwest. The interior of Fizeau is relatively flat beyond the terraces, with only a few low rises in the northwest section of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Doppler Effect
The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described the phenomenon in 1842. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. When the source of the sound wave is moving towards the observer, each successive cycle of the wave is emitted from a position closer to the observer than the previous cycle. Hence, from the observer's perspective, the time between cycles is reduced, meaning the frequency is increased. Conversely, if the source of the sound wave is moving away from the observer, each cycle of the wave is emitted from a position farther from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Induction Coil
An induction coil or "spark coil" ( archaically known as an inductorium or Ruhmkorff coil after Heinrich Rühmkorff) is a type of transformer used to produce high-voltage pulses from a low-voltage direct current (DC) supply. p.98 To create the flux changes necessary to induce voltage in the secondary coil, the direct current in the primary coil is repeatedly interrupted by a vibrating mechanical contact called an interrupter. Invented in 1836 by the Irish-Catholic priest Nicholas Callan, also independently by American inventor Charles Grafton Page, the induction coil was the first type of transformer. It was widely used in x-ray machines, spark-gap radio transmitters, arc lighting and quack medical electrotherapy devices from the 1880s to the 1920s. Today its only common use is as the ignition coils in internal combustion engines and in physics education to demonstrate induction. Construction and function An induction coil consists of two coils of insulated wire wo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of The 72 Names On The Eiffel Tower
On the Eiffel Tower, 72 names of France, French men (scientists, engineers, and mathematicians) are engraved in recognition of their contributions. Gustave Eiffel chose this "invocation of science" because of his concern over the Eiffel Tower#Artists' protest, protests against the tower, and chose names of those who had distinguished themselves since 1789. The engravings are found on the sides of the tower under the first balcony, in letters about tall, and were originally painted in gold. The engraving was painted over at the beginning of the 20th century and restored in 1986–87 by Société Nouvelle d'exploitation de la Tour Eiffel, the company that the city of Paris contracts to operate the Tower. The repainting of 2010–11 restored the letters to their original gold colour. There are also names of the engineers who helped build the Tower and design its architecture on a plaque on the top of the Tower, where a laboratory was built as well. List Location The list is spl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Redshift
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation (such as light). The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a #Blueshift, blueshift. The terms derive from the colours red and blue which form the extremes of the Visible spectrum, visible light spectrum. Three forms of redshift occur in astronomy and cosmology: Doppler effect, Doppler redshifts due to the relative motions of radiation sources, gravitational redshift as radiation escapes from gravitational potentials, and cosmological redshifts of all light sources proportional to their distances from Earth, a fact known as Hubble's law that implies the expansion of the universe, universe is expanding. All redshifts can be understood under the umbrella of Frame of reference, frame transformation laws. Gravitational waves, which also travel at Speed of light, the speed of light, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rumford Medal
The Rumford Medal is an award bestowed by the Royal Society for "outstanding contributions in the field of physics". The award is named in honour of British scientist Sir Benjamin Thompson, Count Rumford, who is noted for his works on thermodynamics and for establishing the Royal Institution. The award was created in 1796 after Thompson transferred £1,000 to the Royal Society in stocks, instructing the latter to grant the awardee the fund's interest as a premium. Thompson was awarded the inaugural award in 1800. The award initially consisted of two medals, one each in silver and gold, struck in the same die. This was later replaced with a single medal made of silver gilt. The medal is awarded with a cash prize of £2,000. British painter Robert Smirke created the original design of the medal. The diameter of the medal is 3 inches (7.62 cm). The obverse featured a tripod altar with a flame upon it, circumscribed by a Latin inscription from Lucretius' poem ''De rerum natura'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
François Arago
Dominique François Jean Arago (), known simply as François Arago (; Catalan: , ; 26 February 17862 October 1853), was a French mathematician, physicist, astronomer, freemason, supporter of the Carbonari revolutionaries and politician. Early life and work Arago was born at Estagel, a small village of 3,000 near Perpignan, in the ' of Pyrénées-Orientales, France, where his father held the position of Treasurer of the Mint. His parents were François Bonaventure Arago (1754–1814) and Marie Arago (1755–1845). Arago was the eldest of four brothers. Jean (1788–1836) emigrated to North America and became a general in the Mexican army. Jacques Arago, Jacques Étienne Victor (1799–1855) took part in Louis de Freycinet's exploring voyage in the ''Uranie'' from 1817 to 1821, and on his return to France devoted himself to his journalism and the drama. The fourth brother, Étienne Arago, Étienne Vincent (1802–1892), is said to have collaborated with Honoré de Balzac in ''The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
