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Thermionic
Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the material. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as thermions. After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region. But if the emitter is connected to a battery, the charge left behind is neutralized by charge supplied by the battery as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The classical example of thermionic emission is that of electrons from a hot cathode into a vacuum (also known as thermal electron emission or the Edison effect) in a vacuum tube. The hot cathode can be a metal filament, a coated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermionic Filament
Thermionic emission is the liberation of electrons from an electrode by virtue of its temperature (releasing of energy supplied by heat). This occurs because the thermal energy given to the charge carrier overcomes the work function of the material. The charge carriers can be electrons or ions, and in older literature are sometimes referred to as thermions. After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region. But if the emitter is connected to a battery, the charge left behind is neutralized by charge supplied by the battery as the emitted charge carriers move away from the emitter, and finally the emitter will be in the same state as it was before emission. The classical example of thermionic emission is that of electrons from a hot cathode into a vacuum (also known as thermal electron emission or the Edison effect) in a vacuum tube. The hot cathode can be a metal filament, a coated ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermionic Converter
A thermionic converter consists of a hot electrode which thermionically emits electrons over a potential energy barrier to a cooler electrode, producing a useful electric power output. Caesium vapor is used to optimize the electrode work functions and provide an ion supply (by surface ionization or electron impact ionization in a plasma) to neutralize the electron space charge. Definition From a physical electronic viewpoint, thermionic energy conversion is the direct production of electric power from heat by thermionic electron emission. From a thermodynamic viewpoint, it is the use of electron vapor as the working fluid in a power-producing cycle. A thermionic converter consists of a hot emitter electrode from which electrons are vaporized by thermionic emission and a colder collector electrode into which they are condensed after conduction through the inter-electrode plasma. The resulting current, typically several amperes per square centimeter of emitter surface, d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrodynamic Tether
Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetism, electromagnetic principles as electrical generator, generators, by converting their kinetic energy to electrical energy, or as electric motor, motors, converting electrical energy to kinetic energy.NASATethers In Space Handbook edited by M.L. Cosmo and E.C. Lorenzini, Third Edition December 1997 (accessed 20 October 2010); see also version aNASA MSFC available oscribd/ref> Electric potential is generated across a conductive tether by its motion through a planet's magnetic field. A number of missions have demonstrated electrodynamic tethers in space, most notably the Space tether missions#TSS-1 mission, TSS-1, Space tether missions#TSS-1R mission, TSS-1R, and Space tether missions#PMG, Plasma Motor Generator (PMG) experiments. Tether propulsion As part of a ''tether propulsion'' system, craft can use long, strong conductors (though not all te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Work Function
In solid-state physics, the work function (sometimes spelt workfunction) is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" means that the final electron position is far from the surface on the atomic scale, but still too close to the solid to be influenced by ambient electric fields in the vacuum. The work function is not a characteristic of a bulk material, but rather a property of the surface of the material (depending on crystal face and contamination). Definition The work function for a given surface is defined by the difference :W = -e\phi - E_, where is the charge of an electron, is the electrostatic potential in the vacuum nearby the surface, and is the Fermi level (electrochemical potential of electrons) inside the material. The term is the energy of an electron at rest in the vacuum nearby the surface. In practice, one directly controls ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vacuum Tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from a hot cathode for fundamental electronic functions such as signal amplification and current rectification. Non-thermionic types such as a vacuum phototube, however, achieve electron emission through the photoelectric effect, and are used for such purposes as the detection of light intensities. In both types, the electrons are accelerated from the cathode to the anode by the electric field in the tube. The simplest vacuum tube, the diode (i.e. Fleming valve), invented in 1904 by John Ambrose Fleming, contains only a heated electron-emitting cathode and an anode. Electrons can only flow in one direction through the device—from the cathode to the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hot Cathode
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating element. The heating element is usually an electrical filament heated by a separate electric current passing through it. Hot cathodes typically achieve much higher power density than cold cathodes, emitting significantly more electrons from the same surface area. Cold cathodes rely on field electron emission or secondary electron emission from positive ion bombardment, and do not require heating. There are two types of hot cathode. In a ''directly heated cathode'', the filament is the cathode and emits the electrons. In an ''indirectly heated cathode'', the filament or ''heater'' heats a separate metal cathode electrode which emits the electrons. From the 1920s to the 1960s, a wide variety of electronic devices used hot-cathode vacuum tub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Ambrose Fleming
Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was an English electrical engineer and physicist who invented the first thermionic valve or vacuum tube, designed the radio transmitter with which the first transatlantic radio transmission was made, and also established the right-hand rule used in physics. He was the eldest of seven children of James Fleming DD (died 1879), a Congregational minister, and his wife Mary Ann, at Lancaster, Lancashire, and baptised on 11 February 1850. A devout Christian, he once preached at St Martin-in-the-Fields in London on evidence for the resurrection. In 1932, he and Douglas Dewar and Bernard Acworth helped establish the Evolution Protest Movement. Fleming bequeathed much of his estate to Christian charities, especially those for the poor. He was a noted photographer, painted watercolours, and enjoyed climbing the Alps. Early years Ambrose Fleming was born in Lancaster and educated at Lancaster Royal Grammar Scho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hans Friedrich Geitel
Hans Friedrich Karl Geitel (16 July 1855 in Braunschweig – 15 August 1923 in Wolfenbüttel) was a German physicist. He is credited with coining the phrase "atomic energy." Biography Through the relocation of his family, his father was a forester, Hans Geitel came to Bad Blankenburg, Blankenburg in 1861 and grew up in close proximity to Julius Elster. He attended school and high school together with Elster. A lifelong friendship developed between the two of them, their interest in science became a shared field of activity. During their studies both spent two years in Heidelberg and Berlin. In 1879 Geitel got his teaching degree in Braunschweig and accepted a position as teacher at the then called Herzogliche Große Schule (translation: Ducal Great School) in Wolfenbüttel. In 1881 Geitel succeeded in getting Julius Elster to the school as well. There they intensified their joint researches. Karl Bergwitz (1875–1958), who continued their research, was one of their students there ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Edmond Becquerel
Alexandre-Edmond Becquerel (24 March 1820 – 11 May 1891), known as Edmond Becquerel, was a French physicist who studied the solar spectrum, magnetism, electricity and optics. He is credited with the discovery of the photovoltaic effect, the operating principle of the solar cell, in 1839. He is also known for his work in luminescence and phosphorescence. He was the son of Antoine César Becquerel and the father of Henri Becquerel, one of the discoverers of radioactivity. Biography Becquerel was born in Paris and was in turn the pupil, assistant and successor of his father at the Muséum national d'Histoire naturelle. He was also appointed professor at the short-lived Agronomic Institute at Versailles in 1849, and in 1853 received the chair of physics at the Conservatoire des Arts et Métiers. He was associated with his father in much of his work. The first photovoltaic device In 1839, at age 19, experimenting in his father's laboratory, Becquerel created the world's fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Charge Carrier
In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used most commonly in solid state physics. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current. In conducting media, particles serve to carry charge: *In many metals, the charge carriers are electrons. One or two of the valence electrons from each atom are able to move about freely within the crystal structure of the metal. The free electrons are referred to as conduction electrons, and the cloud of free electrons is called a Fermi gas. Many metals have electron and hole bands. In some, the majority carriers are holes. *In electrolytes, such as salt water, the charge carriers are ions, which are a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Johann Wilhelm Hittorf
Johann Wilhelm Hittorf (27 March 1824 – 28 November 1914) was a German physicist who was born in Bonn and died in Münster, Germany. Hittorf was the first to compute the electricity-carrying capacity of charged atoms and molecules (ions), an important factor in understanding electrochemical reactions. He formulated ion transport numbers and the first method for their measurements. He observed tubes with energy rays extending from a negative electrode. These rays produced a fluorescence when they hit the glass walls of the tubes. In 1876 the effect was named "cathode rays" by Eugen Goldstein. Hittorf's early investigations were on the allotropes of phosphorus and selenium. Between 1853 and 1859 his most important work was on ion movement caused by electric current. In 1853 Hittorf pointed out that some ions traveled more rapidly than others. This observation led to the concept of transport number, the fraction of the electric current carried by each ionic species. He meas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
McGraw-Hill
McGraw Hill is an American educational publishing company and one of the "big three" educational publishers that publishes educational content, software, and services for pre-K through postgraduate education. The company also publishes reference and trade publications for the medical, business, and engineering professions. McGraw Hill operates in 28 countries, has about 4,000 employees globally, and offers products and services to about 140 countries in about 60 languages. Formerly a division of The McGraw Hill Companies (later renamed McGraw Hill Financial, now S&P Global), McGraw Hill Education was divested and acquired by Apollo Global Management in March 2013 for $2.4 billion in cash. McGraw Hill was sold in 2021 to Platinum Equity for $4.5 billion. Corporate History McGraw Hill was founded in 1888 when James H. McGraw, co-founder of the company, purchased the ''American Journal of Railway Appliances''. He continued to add further publications, eventually establishin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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