1.
System of measurement
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A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce, systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The French Revolution gave rise to the system, and this has spread around the world. In most systems, length, mass, and time are base quantities, later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. Other quantities, such as power and speed, are derived from the set, for example. Such arrangements were satisfactory in their own contexts, the preference for a more universal and consistent system only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained using a more rational system. However pressure built up, including scientists and engineers for conversion to a more rational. The unifying characteristic is that there was some definition based on some standard, eventually cubits and strides gave way to customary units to met the needs of merchants and scientists. In the metric system and other recent systems, a basic unit is used for each base quantity. Often secondary units are derived from the units by multiplying by powers of ten. Thus the basic unit of length is the metre, a distance of 1.234 m is 1,234 millimetres. Metrication is complete or nearly complete in almost all countries, US customary units are heavily used in the United States and to some degree in Liberia. Traditional Burmese units of measurement are used in Burma, U. S. units are used in limited contexts in Canada due to the large volume of trade, there is also considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a used unit for volume, especially on bottles of beverages. Some other standard non-SI units are still in use, such as nautical miles and knots in aviation. Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795, during this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries
2.
SI derived unit
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The International System of Units specifies a set of seven base units from which all other SI units of measurement are derived. Each of these units is either dimensionless or can be expressed as a product of powers of one or more of the base units. For example, the SI derived unit of area is the metre. The degree Celsius has an unclear status, and is arguably an exception to this rule. The names of SI units are written in lowercase, the symbols for units named after persons, however, are always written with an uppercase initial letter. In addition to the two dimensionless derived units radian and steradian,20 other derived units have special names, some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units. Until 1995, the SI classified the radian and the steradian as supplementary units, but this designation was abandoned, International System of Quantities International System of Units International Vocabulary of Metrology Metric prefix Metric system Non-SI units mentioned in the SI Planck units SI base unit I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC, Quantities, Units and Symbols in Physical Chemistry. CS1 maint, Multiple names, authors list
3.
Electrical resistance
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The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which a current passes. Electrical resistance shares some parallels with the notion of mechanical friction. The SI unit of resistance is the ohm, while electrical conductance is measured in siemens. An object of uniform cross section has a proportional to its resistivity and length. All materials show some resistance, except for superconductors, which have a resistance of zero and this proportionality is called Ohms law, and materials that satisfy it are called ohmic materials. In other cases, such as a diode or battery, V and I are not directly proportional. The ratio V/I is sometimes useful, and is referred to as a chordal resistance or static resistance, since it corresponds to the inverse slope of a chord between the origin and an I–V curve. In other situations, the derivative d V d I may be most useful, in the hydraulic analogy, current flowing through a wire is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, the voltage drop, not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar, The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it, for example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be a large water pressure below the pipe. If these pressures are equal, no water flows, in the same way, a long, thin copper wire has higher resistance than a short, thick copper wire. A pipe filled with hair restricts the flow of more than a clean pipe of the same shape. The difference between copper, steel, and rubber is related to their structure and electron configuration. In addition to geometry and material, there are other factors that influence resistance and conductance, such as temperature. Substances in which electricity can flow are called conductors, a piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper, Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs
4.
Georg Ohm
–
Georg Simon Ohm was a German physicist and mathematician. As a school teacher, Ohm began his research with the new electrochemical cell, using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference applied across a conductor and the resultant electric current. This relationship is known as Ohms law, Georg Simon Ohm was born into a Protestant family in Erlangen, Brandenburg-Bayreuth, son to Johann Wolfgang Ohm, a locksmith and Maria Elizabeth Beck, the daughter of a tailor in Erlangen. Of the seven children of the only three survived to adulthood, Georg Simon, his younger brother Martin, who later became a well-known mathematician. His mother died when he was ten, from early childhood, Georg and Martin were taught by their father who brought them to a high standard in mathematics, physics, chemistry and philosophy. This characteristic made the Ohms bear a resemblance to the Bernoulli family, as noted by Karl Christian von Langsdorf, Georg Ohms father, concerned that his son was wasting his educational opportunity, sent Ohm to Switzerland. There in September 1806 Ohm accepted a position as a teacher in a school in Gottstadt bei Nidau. Langsdorf, however, advised Ohm to continue with his studies of mathematics on his own, advising Ohm to read the works of Euler, Laplace and Lacroix. Rather reluctantly Ohm took his advice but he left his teaching post in Gottstatt Monastery in March 1809 to become a tutor in Neuchâtel. For two years he carried out his duties as a tutor while he followed Langsdorfs advice and continued his study of mathematics. Then in April 1811 he returned to the University of Erlangen, Ohms own studies prepared him for his doctorate which he received from the University of Erlangen on October 25,1811. He immediately joined the faculty there as a lecturer in mathematics and he could not survive on his salary as a lecturer. The Bavarian government offered him a post as a teacher of mathematics and physics at a quality school in Bamberg which Ohm accepted in January 1813. Unhappy with his job, Georg began writing a textbook on geometry as a way to prove his abilities. Ohms school was closed down in February 1816, the Bavarian government then sent him to an overcrowded school in Bamberg to help out with the teaching of mathematics. After his assignment in Bamberg, Ohm sent his manuscript to King Wilhelm III of Prussia. The King was satisfied with Ohms book, and offered Ohm a position at the Jesuit Gymnasium of Cologne on 11 September 1817 and this school had a reputation for good science education and Ohm was required to teach physics in addition to mathematics. The physics laboratory was equipped, allowing Ohm to begin experiments in physics
5.
SI base unit
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The International System of Units defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science, thus, the kelvin, named after Lord Kelvin, has the symbol K and the ampere, named after André-Marie Ampère, has the symbol A. Many other units, such as the litre, are not part of the SI. The definitions of the units have been modified several times since the Metre Convention in 1875. Since the redefinition of the metre in 1960, the kilogram is the unit that is directly defined in terms of a physical artifact. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinum–iridium cylinder stored in a vault near Paris. It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, two possibilities have attracted particular attention, the Planck constant and the Avogadro constant. The 23rd CGPM decided to postpone any formal change until the next General Conference in 2011
6.
Kilogram
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The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
7.
Metre
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The metre or meter, is the base unit of length in the International System of Units. The metre is defined as the length of the path travelled by light in a vacuum in 1/299792458 seconds, the metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a metre bar. In 1960, the metre was redefined in terms of a number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted, the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Measuring devices are spelled -meter in all variants of English, the suffix -meter has the same Greek origin as the unit of length. This range of uses is found in Latin, French, English. Thus calls for measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. In 1668, Wilkins proposed using Christopher Wrens suggestion of defining the metre using a pendulum with a length which produced a half-period of one second, christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches. This is the equivalent of what is now known to be 997 mm, no official action was taken regarding this suggestion. In the 18th century, there were two approaches to the definition of the unit of length. One favoured Wilkins approach, to define the metre in terms of the length of a pendulum which produced a half-period of one second. The other approach was to define the metre as one ten-millionth of the length of a quadrant along the Earths meridian, that is, the distance from the Equator to the North Pole. This means that the quadrant would have defined as exactly 10000000 metres at that time. To establish a universally accepted foundation for the definition of the metre, more measurements of this meridian were needed. This portion of the meridian, assumed to be the length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator
8.
Second
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The second is the base unit of time in the International System of Units. It is qualitatively defined as the division of the hour by sixty. SI definition of second is the duration of 9192631770 periods of the corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Seconds may be measured using a mechanical, electrical or an atomic clock, SI prefixes are combined with the word second to denote subdivisions of the second, e. g. the millisecond, the microsecond, and the nanosecond. Though SI prefixes may also be used to form multiples of the such as kilosecond. The second is also the unit of time in other systems of measurement, the centimetre–gram–second, metre–kilogram–second, metre–tonne–second. Absolute zero implies no movement, and therefore zero external radiation effects, the second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. The realization of the second is described briefly in a special publication from the National Institute of Standards and Technology. 1 international second is equal to, 1⁄60 minute 1⁄3,600 hour 1⁄86,400 day 1⁄31,557,600 Julian year 1⁄, more generally, = 1⁄, the Hellenistic astronomers Hipparchus and Ptolemy subdivided the day into sixty parts. They also used an hour, simple fractions of an hour. No sexagesimal unit of the day was used as an independent unit of time. The modern second is subdivided using decimals - although the third remains in some languages. The earliest clocks to display seconds appeared during the last half of the 16th century, the second became accurately measurable with the development of mechanical clocks keeping mean time, as opposed to the apparent time displayed by sundials. The earliest spring-driven timepiece with a hand which marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection. During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute, in 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe redesigned clocks that displayed minutes at his observatory so they also displayed seconds, however, they were not yet accurate enough for seconds. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds, in 1670, London clockmaker William Clement added this seconds pendulum to the original pendulum clock of Christiaan Huygens. From 1670 to 1680, Clement made many improvements to his clock and this clock used an anchor escapement mechanism with a seconds pendulum to display seconds in a small subdial
9.
Ampere
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The ampere, often shortened to amp, is a unit of electric current. In the International System of Units the ampere is one of the seven SI base units and it is named after André-Marie Ampère, French mathematician and physicist, considered the father of electrodynamics. SI defines the ampere in terms of base units by measuring the electromagnetic force between electrical conductors carrying electric current. The ampere was then defined as one coulomb of charge per second, in SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second. In the future, the SI definition may shift back to charge as the base unit, ampères force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the definition of the ampere. The SI unit of charge, the coulomb, is the quantity of electricity carried in 1 second by a current of 1 ampere, conversely, a current of one ampere is one coulomb of charge going past a given point per second,1 A =1 C s. In general, charge Q is determined by steady current I flowing for a time t as Q = It, constant, instantaneous and average current are expressed in amperes and the charge accumulated, or passed through a circuit over a period of time is expressed in coulombs. The relation of the ampere to the coulomb is the same as that of the watt to the joule, the ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart. The size of the unit was chosen so that the derived from it in the MKSA system would be conveniently sized. The international ampere was a realization of the ampere, defined as the current that would deposit 0.001118 grams of silver per second from a silver nitrate solution. Later, more accurate measurements revealed that this current is 0.99985 A, at present, techniques to establish the realization of an ampere have a relative uncertainty of approximately a few parts in 107, and involve realizations of the watt, the ohm and the volt. Rather than a definition in terms of the force between two current-carrying wires, it has proposed that the ampere should be defined in terms of the rate of flow of elementary charges. Since a coulomb is equal to 6. 2415093×1018 elementary charges. The proposed change would define 1 A as being the current in the direction of flow of a number of elementary charges per second. In 2005, the International Committee for Weights and Measures agreed to study the proposed change, the new definition was discussed at the 25th General Conference on Weights and Measures in 2014 but for the time being was not adopted. The current drawn by typical constant-voltage energy distribution systems is usually dictated by the power consumed by the system, for this reason the examples given below are grouped by voltage level
10.
Omega
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Omega is the 24th and last letter of the Greek alphabet. In the Greek numeric system, it has a value of 800, the word literally means great O, as opposed to omicron, which means little O. In phonetic terms, the Ancient Greek Ω is a long open-mid o, in Modern Greek, Ω represents the mid back rounded vowel /o/, the same sound as omicron. The letter omega is transcribed ō or simply o, as the last letter of the Greek alphabet, Omega is often used to denote the last, the end, or the ultimate limit of a set, in contrast to alpha, the first letter of the Greek alphabet. Ω was not part of the early Greek alphabets and it was introduced in the late 7th century BC in the Ionian cities of Asia Minor to denote the long half-open. It is a variant of omicron, broken up at the side, the name Ωμέγα is Byzantine, in Classical Greek, the letter was called ō, whereas the omicron was called ou. In addition to the Greek alphabet, Omega was also adopted into the early Cyrillic alphabet, a Raetic variant is conjectured to be at the origin or parallel evolution of the Elder Futhark ᛟ. Omega was also adopted into the Latin alphabet, as a letter of the 1982 revision to the African reference alphabet, the uppercase letter Ω is used as a symbol, In chemistry, For oxygen-18, a natural, stable isotope of oxygen. In physics, For ohm – SI unit of resistance, formerly also used upside down to represent mho. Unicode has a code point for the ohm sign, but it is included only for backward compatibility. In statistical mechanics, Ω refers to the multiplicity in a system, the solid angle or the rate of precession in a gyroscope. In particle physics to represent the Omega baryons, in astronomy, Ω refers to the density of the universe, also called the density parameter. In astronomy, Ω refers to the longitude of the node of an orbit. In mathematics and computer science, In complex analysis, the Omega constant, a solution of Lamberts W function In differential geometry, a variable for a 2-dimensional region in calculus, usually corresponding to the domain of a double integral. In topos theory, the subobject classifier of an elementary topos, in combinatory logic, the looping combinator, In group theory, the omega and agemo subgroups of a p-group, Ω and ℧ In group theory, Cayleys Ω process as a partial differential operator. In statistics, it is used as the symbol for the sample space, in number theory, Ω is the number of prime divisors of n. In notation related to Big O notation to describe the behavior of functions. As part of logo or trademark, The logo of Omega Watches SA, part of the Badge of the Supreme Court of the United Kingdom
11.
Georg Simon Ohm
–
Georg Simon Ohm was a German physicist and mathematician. As a school teacher, Ohm began his research with the new electrochemical cell, using equipment of his own creation, Ohm found that there is a direct proportionality between the potential difference applied across a conductor and the resultant electric current. This relationship is known as Ohms law, Georg Simon Ohm was born into a Protestant family in Erlangen, Brandenburg-Bayreuth, son to Johann Wolfgang Ohm, a locksmith and Maria Elizabeth Beck, the daughter of a tailor in Erlangen. Of the seven children of the only three survived to adulthood, Georg Simon, his younger brother Martin, who later became a well-known mathematician. His mother died when he was ten, from early childhood, Georg and Martin were taught by their father who brought them to a high standard in mathematics, physics, chemistry and philosophy. This characteristic made the Ohms bear a resemblance to the Bernoulli family, as noted by Karl Christian von Langsdorf, Georg Ohms father, concerned that his son was wasting his educational opportunity, sent Ohm to Switzerland. There in September 1806 Ohm accepted a position as a teacher in a school in Gottstadt bei Nidau. Langsdorf, however, advised Ohm to continue with his studies of mathematics on his own, advising Ohm to read the works of Euler, Laplace and Lacroix. Rather reluctantly Ohm took his advice but he left his teaching post in Gottstatt Monastery in March 1809 to become a tutor in Neuchâtel. For two years he carried out his duties as a tutor while he followed Langsdorfs advice and continued his study of mathematics. Then in April 1811 he returned to the University of Erlangen, Ohms own studies prepared him for his doctorate which he received from the University of Erlangen on October 25,1811. He immediately joined the faculty there as a lecturer in mathematics and he could not survive on his salary as a lecturer. The Bavarian government offered him a post as a teacher of mathematics and physics at a quality school in Bamberg which Ohm accepted in January 1813. Unhappy with his job, Georg began writing a textbook on geometry as a way to prove his abilities. Ohms school was closed down in February 1816, the Bavarian government then sent him to an overcrowded school in Bamberg to help out with the teaching of mathematics. After his assignment in Bamberg, Ohm sent his manuscript to King Wilhelm III of Prussia. The King was satisfied with Ohms book, and offered Ohm a position at the Jesuit Gymnasium of Cologne on 11 September 1817 and this school had a reputation for good science education and Ohm was required to teach physics in addition to mathematics. The physics laboratory was equipped, allowing Ohm to begin experiments in physics
12.
British Association for the Advancement of Science
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The British Science Association is a charity and learned society founded in 1831 to aid in the promotion and development of science. Until 2009 it was known as the British Association for the Advancement of Science, the Association was founded in 1831 and modelled on the German Gesellschaft Deutscher Naturforscher und Ärzte. The prime mover was Reverend William Vernon Harcourt, following a suggestion by Sir David Brewster, Brewster, Charles Babbage, William Whewell and J. F. W. Johnston are also considered to be founding members. The first meeting was held in York on Tuesday 27 September 1831 with various scientific papers being presented on the following days and it was chaired by Viscount Milton, President of the Yorkshire Philosophical Society, and upwards of 300 gentlemen attended the meeting. The newspaper published the names of over a hundred of those attending, from that date onwards a meeting was held annually at a place chosen at a previous meeting. In 1832, for example, the meeting was held in Oxford, by this stage the Association had four sections, Physics, Chemistry, Geology and Natural History. A very important decision in the Association’s history was made in 1842 when it was resolved to create a “physical observatory”, a building that became well known as the Kew Observatory was taken on for the purpose and Francis Ronalds was chosen as the inaugural Honorary Director. Kew Observatory quickly became one of the most renowned meteorological and geomagnetic observatories in the world, one of the most famous events linked to the Association Meeting was an exchange between Thomas Henry Huxley and Bishop Samuel Wilberforce in 1860. Although a number of newspapers made passing references to the exchange, a need for standards arose with the submarine telegraph industry. The undertaking was suggested to the BA by William Thomson, josiah Latimer Clark and Fleeming Jenkin made preparations. Thomson, with his students, found that copper, contaminated with arsenic. The chemist Augustus Matthiessen contributed an appendix to the final 1873 report that showed temperature-dependence of alloys, the Association introduced the British Association screw threads, a series of screw thread standards in sizes from 0. 25mm up to 6mm, in 1884. The standards were ahead of their time in that they were based on the metric system and they remained in general use for instruments and small assemblies until metrication in the 1970s. A decision that became notorious in the century was made in 1878 when a committee of the Association recommended against constructing Charles Babbages analytical engine. The Association was parodied by English novelist Charles Dickens as The Mudfog Society for the Advancement of Everything in The Mudfog Papers, the Associations main aim is to improve the perception of science and scientists in the UK. Prof Sir George Porter, on becoming President in September 1985, was scathing against so-called soft sciences such as psychology and he claimed this was damaging the public perception of science. We run the risk of doing neither well, universities are underfunded, and must not be seen simply as a substitute for National Service to keep youngsters off the dole queue. He also said scientists have to be careful and consider the implications of what they are seeking to achieve
13.
Quantum Hall effect
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The prefactor, ν is known as the filling factor, and can take on either integer or fractional values. The quantum Hall effect is referred to as the integer or fractional quantum Hall effect depending on whether ν is an integer or fraction, the striking feature of the integer quantum Hall effect is the persistence of the quantization as the electron density is varied. The fractional quantum Hall effect is more complicated, as its existence relies fundamentally on electron–electron interactions, although the microscopic origins of the fractional quantum Hall effect are unknown, there are several phenomenological approaches that provide accurate approximations. For example, the effect can be thought of as an integer quantum Hall effect, not of electrons, in 1988, it was proposed that there was quantum Hall effect without Landau levels. This quantum Hall effect is referred to as the quantum anomalous Hall effect, there is also a new concept of the quantum spin Hall effect which is an analogue of the quantum Hall effect, where spin currents flow instead of charge currents. The quantization of the Hall conductance has the important property of being exceedingly precise, actual measurements of the Hall conductance have been found to be integer or fractional multiples of e2/h to nearly one part in a billion. This phenomenon, referred to as exact quantization, has shown to be a subtle manifestation of the principle of gauge invariance. It has allowed for the definition of a new standard for electrical resistance. This is named after Klaus von Klitzing, the discoverer of exact quantization, since 1990, a fixed conventional value RK-90 is used in resistance calibrations worldwide. The quantum Hall effect also provides an extremely precise independent determination of the structure constant. Several researchers subsequently observed the effect in experiments carried out on the layer of MOSFETs. For this finding, von Klitzing was awarded the 1985 Nobel Prize in Physics, the link between exact quantization and gauge invariance was subsequently found by Robert Laughlin, who connected the quantized conductivity to the quantized charge transport in Thouless charge pump. Most integer quantum Hall experiments are now performed on gallium arsenide heterostructures, in 2007, the integer quantum Hall effect was reported in graphene at temperatures as high as room temperature, and in the oxide ZnO-MgxZn1−xO. In two dimensions, when electrons are subjected to a magnetic field they follow circular cyclotron orbits. When the system is treated quantum mechanically, these orbits are quantized, the energy levels of these quantized orbitals take on discrete values, E n = ℏ ω c, where ωc = eB/m is the cyclotron frequency. For strong magnetic fields, each Landau level is highly degenerate, the integers that appear in the Hall effect are examples of topological quantum numbers. They are known in mathematics as the first Chern numbers and are related to Berrys phase. A striking model of much interest in this context is the Azbel-Harper-Hofstadter model whose quantum phase diagram is the Hofstadter butterfly shown in the figure, the vertical axis is the strength of the magnetic field and the horizontal axis is the chemical potential, which fixes the electron density
14.
Multimeter
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A multimeter or a multitester, also known as a VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can measure voltage, current, and resistance, analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters have a display, and may also show a graphical bar representing the measured value. Digital multimeters are now far more due to their cost and precision. A multimeter can be a device useful for basic fault finding and field service work. Multimeters are available in a range of features and prices. Cheap multimeters can cost less than US$10, while models with certified calibration can cost more than US$5,000. The first moving-pointer current-detecting device was the galvanometer in 1820 and these were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and these galvanometers were bulky and delicate. The DArsonval/Weston meter movement uses a coil which carries a pointer. The coil rotates in a permanent magnetic field and is restrained by fine spiral springs which also serve to carry current into the moving coil and it gives proportional measurement rather than just detection, and deflection is independent of the orientation of the meter. Instead of balancing a bridge, values could be read off the instruments scale. The basic moving coil meter is only for direct current measurements. It is easily adapted to read heavier currents by using shunts or to voltage using series resistances known as multipliers. To read alternating currents or voltages, a rectifier is needed, multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. Macadie invented an instrument which could measure amperes, volts and ohms, the meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. The Automatic Coil Winder and Electrical Equipment Company was set up to manufacture the Avometer, although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927, Automatic Coil Winder and Electrical Equipment Company
15.
Volt
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The volt is the derived unit for electric potential, electric potential difference, and electromotive force. One volt is defined as the difference in potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can also be expressed as amperes times ohms, watts per ampere, or joules per coulomb, for the Josephson constant, KJ = 2e/h, the conventional value KJ-90 is used, K J-90 =0.4835979 GHz μ V. This standard is typically realized using an array of several thousand or tens of thousands of junctions. Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc. in the water-flow analogy sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping, the relationship between voltage and current is defined by Ohms Law. Ohms Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems, the voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. Cells can be combined in series for multiples of that voltage, mechanical generators can usually be constructed to any voltage in a range of feasibility. High-voltage electric power lines,110 kV and up Lightning, Varies greatly. Volta had determined that the most effective pair of metals to produce electricity was zinc. In 1861, Latimer Clark and Sir Charles Bright coined the name volt for the unit of resistance, by 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission and they made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. At that time, the volt was defined as the difference across a conductor when a current of one ampere dissipates one watt of power. The international volt was defined in 1893 as 1/1.434 of the emf of a Clark cell and this definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of reproducible units was abandoned in 1948. Prior to the development of the Josephson junction voltage standard, the volt was maintained in laboratories using specially constructed batteries called standard cells
16.
Electromotive force
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Electromotive force, also called emf, is the voltage developed by any source of electrical energy such as a battery or dynamo. It is generally defined as the potential for a source in a circuit. A device that supplies electrical energy is called electromotive force or emf, emfs convert chemical, mechanical, and other forms of energy into electrical energy. The product of such a device is known as emf. The word force in case is not used to mean mechanical force, measured in newtons. In electromagnetic induction, emf can be defined around a loop as the electromagnetic work that would be done on a charge if it travels once around that loop. This potential difference can drive a current if a circuit is attached to the terminals. Devices that can provide emf include electrochemical cells, thermoelectric devices, solar cells, photodiodes, electrical generators, transformer, in nature, emf is generated whenever magnetic field fluctuations occur through a surface. The shifting of the Earths magnetic field during a geomagnetic storm, … By chemical, mechanical or other means, the source of emf performs work dW on that charge to move it to the high potential terminal. The emf ℰ of the source is defined as the work dW done per charge dq, in the open-circuit case, charge separation continues until the electrical field from the separated charges is sufficient to arrest the reactions. Again the emf is countered by the voltage due to charge separation. If a load is attached, this voltage can drive a current, the general principle governing the emf in such electrical machines is Faradays law of induction. Electromotive force is often denoted by E or ℰ, in a device without internal resistance, if an electric charge Q passes through that device, and gains an energy W, the net emf for that device is the energy gained per unit charge, or J/Q. Like other measures of energy per charge, emf has SI units of volts, Electromotive force in electrostatic units is the statvolt. Inside a source of emf that is open-circuited, the electrostatic field created by separation of charge exactly cancels the forces producing the emf. Thus, the emf has the same value but opposite sign as the integral of the field aligned with an internal path between two terminals A and B of a source of emf in open-circuit condition. This equation applies only to locations A and B that are terminals and this equation involves the electrostatic electric field due to charge separation Ecs and does not involve any non-conservative component of electric field due to Faradays law of induction. The electrostatic field does not contribute to the net emf around a circuit because the portion of the electric field is conservative
17.
Siemens (unit)
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The siemens is the unit of electric conductance, electric susceptance and electric admittance in the International System of Units. The 14th General Conference on Weights and Measures approved the addition of the siemens as a unit in 1971. The unit is named after Ernst Werner von Siemens, as with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case, the lower-case s is the symbol for the second. When an SI unit is spelled out in English, it should begin with a lower-case letter. In English, the same form siemens is used both for the singular and plural, the unit siemens for the conductance G is defined by S = Ω −1 = A V where Ω is the ohm, A is the ampere, and V is the volt. For a device with a conductance of one siemens, the current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device. The conductance of a resistor with a resistance of five ohms, for example, is −1, mho /moʊ/ is an alternative name of the same unit, the reciprocal of one ohm. Mho is derived from spelling ohm backwards and is written with an upside-down capital Greek letter Omega, ℧, according to Maver the term mho was suggested by Sir William Thomson. The mho was officially renamed to the siemens, replacing the old meaning of the siemens unit, the term siemens, as it is an SI term, is used universally in science and often in electrical applications, while mho is still used primarily in electronic applications. Likewise, it is difficult to distinguish the symbol S from the lower-case s where second is meant, brochure The International System of Units issued by the BIPM Different units named after Siemens
18.
Farad
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The farad is the SI derived unit of electrical capacitance, the ability of a body to store an electrical charge. It is named after the English physicist Michael Faraday, one farad is defined as the capacitance across which, when charged with one coulomb, there is a potential difference of one volt. Equally, one farad can be described as the capacitance which stores a one-coulomb charge across a potential difference of one volt, the relationship between capacitance, charge and potential difference is linear. For example, if the difference across a capacitor is halved. For most applications, the farad is a large unit of capacitance. Most electrical and electronic applications are covered by the following SI prefixes,1 mF =1000 μF =1000000 nF1 μF =0.000001 F =1000 nF =1000000 pF1 nF =0. In 1881 at the International Congress of Electricians in Paris, the name farad was officially used for the unit of electrical capacitance, a capacitor consists of two conducting surfaces, frequently referred to as plates, separated by an insulating layer usually referred to as a dielectric. The original capacitor was the Leyden jar developed in the 18th century and it is the accumulation of electric charge on the plates that results in capacitance. Values of capacitors are specified in farads, microfarads, nanofarads and picofarads. The millifarad is rarely used in practice, while the nanofarad is uncommon in North America, the size of commercially available capacitors ranges from around 0.1 pF to 5000F supercapacitors. Capacitance values of 1 pF or lower can be achieved by twisting two short lengths of insulated wire together, the capacitance of the Earths ionosphere with respect to the ground is calculated to be about 1 F. The picofarad is sometimes pronounced as puff or pic, as in a ten-puff capacitor. Similarly, mic is sometimes used informally to signify microfarads, if the Greek letter μ is not available, the notation uF is often used as a substitute for μF in electronics literature. A micro-microfarad, an obsolete unit sometimes found in texts, is the equivalent of a picofarad. In texts prior to 1960, and on capacitor packages even more recently. Similarly, mmf or MMFD represented picofarads, the reciprocal of capacitance is called electrical elastance, the unit of which is the daraf. The abfarad is an obsolete CGS unit of equal to 109 farads. The statfarad is a rarely used CGS unit equivalent to the capacitance of a capacitor with a charge of 1 statcoulomb across a potential difference of 1 statvolt and it is 1/ farad, approximately 1.1126 picofarads
19.
Joule
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The joule, symbol J, is a derived unit of energy in the International System of Units. It is equal to the transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when a current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule, one joule can also be defined as, The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb volt. This relationship can be used to define the volt, the work required to produce one watt of power for one second, or one watt second. This relationship can be used to define the watt and this SI unit is named after James Prescott Joule. As with every International System of Units unit named for a person, note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. The CGPM has given the unit of energy the name Joule, the use of newton metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications. The distinction may be also in the fact that energy is a scalar – the dot product of a vector force. By contrast, torque is a vector – the cross product of a distance vector, torque and energy are related to one another by the equation E = τ θ, where E is energy, τ is torque, and θ is the angle swept. Since radians are dimensionless, it follows that torque and energy have the same dimensions, one joule in everyday life represents approximately, The energy required to lift a medium-size tomato 1 m vertically from the surface of the Earth. The energy released when that same tomato falls back down to the ground, the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space. The heat required to raise the temperature of 1 g of water by 0.24 °C, the typical energy released as heat by a person at rest every 1/60 s. The kinetic energy of a 50 kg human moving very slowly, the kinetic energy of a 56 g tennis ball moving at 6 m/s. The kinetic energy of an object with mass 1 kg moving at √2 ≈1.4 m/s, the amount of electricity required to light a 1 W LED for 1 s. Since the joule is also a watt-second and the unit for electricity sales to homes is the kW·h. For additional examples, see, Orders of magnitude The zeptojoule is equal to one sextillionth of one joule,160 zeptojoules is equivalent to one electronvolt. The nanojoule is equal to one billionth of one joule, one nanojoule is about 1/160 of the kinetic energy of a flying mosquito
20.
Coulomb
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The coulomb is the International System of Units unit of electric charge. 242×1018 protons, and −1 C is equivalent to the charge of approximately 6. 242×1018 electrons. This SI unit is named after Charles-Augustin de Coulomb, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, the SI system defines the coulomb in terms of the ampere and second,1 C =1 A ×1 s. The second is defined in terms of a frequency emitted by caesium atoms. The ampere is defined using Ampères force law, the definition relies in part on the mass of the prototype kilogram. In practice, the balance is used to measure amperes with the highest possible accuracy. One coulomb is the magnitude of charge in 6. 24150934×10^18 protons or electrons. The inverse of this gives the elementary charge of 1. 6021766208×10−19 C. The magnitude of the charge of one mole of elementary charges is known as a faraday unit of charge. In terms of Avogadros number, one coulomb is equal to approximately 1.036 × NA×10−5 elementary charges, one ampere-hour =3600 C,1 mA⋅h =3.6 C. One statcoulomb, the obsolete CGS electrostatic unit of charge, is approximately 3. 3356×10−10 C or about one-third of a nanocoulomb, the elementary charge, the charge of a proton, is approximately 1. 6021766208×10−19 C. In SI, the charge in coulombs is an approximate value. However, in other systems, the elementary charge has an exact value by definition. Specifically, e90 = / C exactly, SI itself may someday change its definitions in a similar way. For example, one possible proposed redefinition is the ampere. is such that the value of the charge e is exactly 1. 602176487×10−19 coulombs. This proposal is not yet accepted as part of the SI, the charges in static electricity from rubbing materials together are typically a few microcoulombs. The amount of charge that travels through a lightning bolt is typically around 15 C, the amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about 5 kC =5000 C ≈1400 mA⋅h. The hydraulic analogy uses everyday terms to illustrate movement of charge, the analogy equates charge to a volume of water, and voltage to pressure
21.
Resistor
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A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active elements, and terminate transmission lines, among other uses. High-power resistors that can dissipate many watts of power as heat may be used as part of motor controls, in power distribution systems. Fixed resistors have resistances that only slightly with temperature, time or operating voltage. Variable resistors can be used to adjust circuit elements, or as sensing devices for heat, light, humidity, force, Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical resistors as discrete components can be composed of various compounds, Resistors are also implemented within integrated circuits. The electrical function of a resistor is specified by its resistance, the nominal value of the resistance falls within the manufacturing tolerance, indicated on the component. Two typical schematic diagram symbols are as follows, The notation to state a resistors value in a circuit diagram varies, one common scheme is the letter and digit code for resistance values following IEC60062. It avoids using a separator and replaces the decimal separator with a letter loosely associated with SI prefixes corresponding with the parts resistance. For example, 8K2 as part marking code, in a diagram or in a bill of materials indicates a resistor value of 8.2 kΩ. Additional zeros imply a tighter tolerance, for example 15M0 for three significant digits, when the value can be expressed without the need for a prefix, an R is used instead of the decimal separator. For example, 1R2 indicates 1.2 Ω, and 18R indicates 18 Ω, for example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a current of 12 /300 =0.04 amperes flows through that resistor. Practical resistors also have some inductance and capacitance which affect the relation between voltage and current in alternating current circuits, the ohm is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere, since resistors are specified and manufactured over a very large range of values, the derived units of milliohm, kilohm, and megohm are also in common usage. The total resistance of resistors connected in series is the sum of their resistance values. R e q = R1 + R2 + ⋯ + R n, the total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the individual resistors. 1 R e q =1 R1 +1 R2 + ⋯ +1 R n. For example, a 10 ohm resistor connected in parallel with a 5 ohm resistor, a resistor network that is a combination of parallel and series connections can be broken up into smaller parts that are either one or the other
22.
Thermistor
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A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor, thermistors are widely used as inrush current limiter, temperature sensors, self-resetting overcurrent protectors, and self-regulating heating elements. Thermistors are of two fundamental types, With NTC, resistance decreases as temperature rises to protect against inrush overvoltage conditions. Commonly installed in parallel as a current sink, with PTC, resistance increases as temperature rises to protect against overcurrent conditions. Commonly installed in series as a resettable fuse, thermistors differ from resistance temperature detectors in that the material used in a thermistor is generally a ceramic or polymer, while RTDs use pure metals. If k is positive, the resistance increases with increasing temperature, if k is negative, the resistance decreases with increasing temperature, and the device is called a negative temperature coefficient thermistor. Resistors that are not thermistors are designed to have a k as close to 0 as possible, instead of the temperature coefficient k, sometimes the temperature coefficient of resistance α T is used. It is defined as α T =1 R d R d T and this α T coefficient should not be confused with the a parameter below. In practice, the linear approximation works only over a temperature range. For accurate temperature measurements, the curve of the device must be described in more detail. The Steinhart–Hart equation is a widely used third-order approximation,1 T = a + b ln + c 3 where a, b and c are called the Steinhart–Hart parameters, T is the absolute temperature and R is the resistance. As an example, typical values for a thermistor with a resistance of 3 kΩ at room temperature are, a =1.40 ×10 −3 b =2.37 ×10 −4 c =9. Solving for R yields, R = R0 e − B or, alternatively and this can be solved for the temperature, T = B ln The B-parameter equation can also be written as ln R = B / T + ln r ∞. This can be used to convert the function of resistance vs. temperature of a thermistor into a function of ln R vs.1 / T. The average slope of this function will yield an estimate of the value of the B parameter. Many NTC thermistors are made from a disc, rod, plate. They work because raising the temperature of a semiconductor increases the number of charge carriers - it promotes them into the conduction band. The more charge carriers that are available, the current a material can conduct
23.
Electrical impedance
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Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. In quantitative terms, it is the ratio of the voltage to the current in an alternating current circuit. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current, there is no distinction between impedance and resistance, the latter can be thought of as impedance with zero phase angle. The impedance caused by two effects is collectively referred to as reactance and forms the imaginary part of complex impedance whereas resistance forms the real part. The symbol for impedance is usually Z and it may be represented by writing its magnitude, however, cartesian complex number representation is often more powerful for circuit analysis purposes. The term impedance was coined by Oliver Heaviside in July 1886, arthur Kennelly was the first to represent impedance with complex numbers in 1893. Impedance is defined as the frequency ratio of the voltage to the current. In other words, it is the voltage–current ratio for a complex exponential at a particular frequency ω. In general, impedance will be a number, with the same units as resistance. For a sinusoidal current or voltage input, the form of the complex impedance relates the amplitude and phase of the voltage. In particular, The magnitude of the impedance is the ratio of the voltage amplitude to the current amplitude. The phase of the impedance is the phase shift by which the current lags the voltage. The reciprocal of impedance is admittance, Impedance is represented as a complex quantity Z and the term complex impedance may be used interchangeably. J is the unit, and is used instead of i in this context to avoid confusion with the symbol for electric current. In Cartesian form, impedance is defined as Z = R + j X where the part of impedance is the resistance R. Where it is needed to add or subtract impedances, the form is more convenient, but when quantities are multiplied or divided. A circuit calculation, such as finding the total impedance of two impedances in parallel, may require conversion between forms several times during the calculation, conversion between the forms follows the normal conversion rules of complex numbers
24.
Electric conductance
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The electrical resistance of an electrical conductor is a measure of the difficulty to pass an electric current through that conductor. The inverse quantity is electrical conductance, and is the ease with which a current passes. Electrical resistance shares some parallels with the notion of mechanical friction. The SI unit of resistance is the ohm, while electrical conductance is measured in siemens. An object of uniform cross section has a proportional to its resistivity and length. All materials show some resistance, except for superconductors, which have a resistance of zero and this proportionality is called Ohms law, and materials that satisfy it are called ohmic materials. In other cases, such as a diode or battery, V and I are not directly proportional. The ratio V/I is sometimes useful, and is referred to as a chordal resistance or static resistance, since it corresponds to the inverse slope of a chord between the origin and an I–V curve. In other situations, the derivative d V d I may be most useful, in the hydraulic analogy, current flowing through a wire is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, the voltage drop, not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar, The pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it, for example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be a large water pressure below the pipe. If these pressures are equal, no water flows, in the same way, a long, thin copper wire has higher resistance than a short, thick copper wire. A pipe filled with hair restricts the flow of more than a clean pipe of the same shape. The difference between copper, steel, and rubber is related to their structure and electron configuration. In addition to geometry and material, there are other factors that influence resistance and conductance, such as temperature. Substances in which electricity can flow are called conductors, a piece of conducting material of a particular resistance meant for use in a circuit is called a resistor. Conductors are made of high-conductivity materials such as metals, in particular copper, Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs
25.
Mho
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The siemens is the unit of electric conductance, electric susceptance and electric admittance in the International System of Units. The 14th General Conference on Weights and Measures approved the addition of the siemens as a unit in 1971. The unit is named after Ernst Werner von Siemens, as with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case, the lower-case s is the symbol for the second. When an SI unit is spelled out in English, it should begin with a lower-case letter. In English, the same form siemens is used both for the singular and plural, the unit siemens for the conductance G is defined by S = Ω −1 = A V where Ω is the ohm, A is the ampere, and V is the volt. For a device with a conductance of one siemens, the current through the device will increase by one ampere for every increase of one volt of electric potential difference across the device. The conductance of a resistor with a resistance of five ohms, for example, is −1, mho /moʊ/ is an alternative name of the same unit, the reciprocal of one ohm. Mho is derived from spelling ohm backwards and is written with an upside-down capital Greek letter Omega, ℧, according to Maver the term mho was suggested by Sir William Thomson. The mho was officially renamed to the siemens, replacing the old meaning of the siemens unit, the term siemens, as it is an SI term, is used universally in science and often in electrical applications, while mho is still used primarily in electronic applications. Likewise, it is difficult to distinguish the symbol S from the lower-case s where second is meant, brochure The International System of Units issued by the BIPM Different units named after Siemens
26.
Multiplicative inverse
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In mathematics, a multiplicative inverse or reciprocal for a number x, denoted by 1/x or x−1, is a number which when multiplied by x yields the multiplicative identity,1. The multiplicative inverse of a fraction a/b is b/a, for the multiplicative inverse of a real number, divide 1 by the number. For example, the reciprocal of 5 is one fifth, the reciprocal function, the function f that maps x to 1/x, is one of the simplest examples of a function which is its own inverse. In the phrase multiplicative inverse, the qualifier multiplicative is often omitted, multiplicative inverses can be defined over many mathematical domains as well as numbers. In these cases it can happen that ab ≠ ba, then inverse typically implies that an element is both a left and right inverse. The notation f −1 is sometimes used for the inverse function of the function f. For example, the multiplicative inverse 1/ = −1 is the cosecant of x, only for linear maps are they strongly related. The terminology difference reciprocal versus inverse is not sufficient to make this distinction, since many authors prefer the opposite naming convention, in the real numbers, zero does not have a reciprocal because no real number multiplied by 0 produces 1. With the exception of zero, reciprocals of every real number are real, reciprocals of every rational number are rational, the property that every element other than zero has a multiplicative inverse is part of the definition of a field, of which these are all examples. On the other hand, no other than 1 and −1 has an integer reciprocal. In modular arithmetic, the multiplicative inverse of a is also defined. This multiplicative inverse exists if and only if a and n are coprime, for example, the inverse of 3 modulo 11 is 4 because 4 ·3 ≡1. The extended Euclidean algorithm may be used to compute it, the sedenions are an algebra in which every nonzero element has a multiplicative inverse, but which nonetheless has divisors of zero, i. e. nonzero elements x, y such that xy =0. A square matrix has an inverse if and only if its determinant has an inverse in the coefficient ring, the linear map that has the matrix A−1 with respect to some base is then the reciprocal function of the map having A as matrix in the same base. Thus, the two notions of the inverse of a function are strongly related in this case, while they must be carefully distinguished in the general case. A ring in which every element has a multiplicative inverse is a division ring. As mentioned above, the reciprocal of every complex number z = a + bi is complex. In particular, if ||z||=1, then 1 / z = z ¯, consequently, the imaginary units, ±i, have additive inverse equal to multiplicative inverse, and are the only complex numbers with this property
27.
Ohm's Law
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Ohms law states that the current through a conductor between two points is directly proportional to the voltage across the two points. More specifically, Ohms law states that the R in this relation is constant, independent of the current and he presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the form of Ohms law. In physics, the term Ohms law is used to refer to various generalizations of the law originally formulated by Ohm. This reformulation of Ohms law is due to Gustav Kirchhoff, in January 1781, before Georg Ohms work, Henry Cavendish experimented with Leyden jars and glass tubes of varying diameter and length filled with salt solution. He measured the current by noting how strong a shock he felt as he completed the circuit with his body, Cavendish wrote that the velocity varied directly as the degree of electrification. He did not communicate his results to other scientists at the time, francis Ronalds delineated “intensity” and “quantity” for the dry pile – a high voltage source – in 1814 using a gold-leaf electrometer. He found for a dry pile that the relationship between the two parameters was not proportional under certain meteorological conditions, Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book Die galvanische Kette, mathematisch bearbeitet. He drew considerable inspiration from Fouriers work on heat conduction in the explanation of his work. For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a stable voltage source in terms of internal resistance. He used a galvanometer to measure current, and knew that the voltage between the terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, from this, Ohm determined his law of proportionality and published his results. Ohms law was probably the most important of the early descriptions of the physics of electricity. We consider it almost obvious today, when Ohm first published his work, this was not the case, critics reacted to his treatment of the subject with hostility. They called his work a web of naked fancies and the German Minister of Education proclaimed that a professor who preached such heresies was unworthy to teach science, also, Ohms brother Martin, a mathematician, was battling the German educational system. These factors hindered the acceptance of Ohms work, and his work did not become widely accepted until the 1840s, fortunately, Ohm received recognition for his contributions to science well before he died. While the old term for electrical conductance, the mho, is used, a new name. The siemens is preferred in formal papers, Ohms work long preceded Maxwells equations and any understanding of frequency-dependent effects in AC circuits
28.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
29.
Alternating current
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Alternating current, is an electric current which periodically reverses direction, whereas direct current flows only in one direction. A common source of DC power is a cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, the usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves, audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current carry information encoded onto the AC signal and these currents typically alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer, use of a higher voltage leads to significantly more efficient transmission of power. The power losses in a conductor are a product of the square of the current and this means that when transmitting a fixed power on a given wire, if the current is halved, the power loss will be four times less. Power is often transmitted at hundreds of kilovolts, and transformed to 100–240 volts for domestic use, high voltages have disadvantages, such as the increased insulation required, and generally increased difficulty in their safe handling. In a power plant, energy is generated at a convenient voltage for the design of a generator, near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world, high-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. HVDC systems, however, tend to be expensive and less efficient over shorter distances than transformers. Three-phase electrical generation is very common, the simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other, if coils are added opposite to these, they generate the same phases with reverse polarity and so can be simply wired together. In practice, higher pole orders are commonly used, for example, a 12-pole machine would have 36 coils. The advantage is that lower rotational speeds can be used to generate the same frequency, for example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency, the lower speed is preferable for larger machines. If the load on a system is balanced equally among the phases. Even in the worst-case unbalanced load, the current will not exceed the highest of the phase currents
30.
Integral
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In mathematics, an integral assigns numbers to functions in a way that can describe displacement, area, volume, and other concepts that arise by combining infinitesimal data. Integration is one of the two operations of calculus, with its inverse, differentiation, being the other. The area above the x-axis adds to the total and that below the x-axis subtracts from the total, roughly speaking, the operation of integration is the reverse of differentiation. For this reason, the integral may also refer to the related notion of the antiderivative. In this case, it is called an integral and is written. The integrals discussed in this article are those termed definite integrals, a rigorous mathematical definition of the integral was given by Bernhard Riemann. It is based on a procedure which approximates the area of a curvilinear region by breaking the region into thin vertical slabs. A line integral is defined for functions of two or three variables, and the interval of integration is replaced by a curve connecting two points on the plane or in the space. In a surface integral, the curve is replaced by a piece of a surface in the three-dimensional space and this method was further developed and employed by Archimedes in the 3rd century BC and used to calculate areas for parabolas and an approximation to the area of a circle. A similar method was developed in China around the 3rd century AD by Liu Hui. This method was used in the 5th century by Chinese father-and-son mathematicians Zu Chongzhi. The next significant advances in integral calculus did not begin to appear until the 17th century, further steps were made in the early 17th century by Barrow and Torricelli, who provided the first hints of a connection between integration and differentiation. Barrow provided the first proof of the theorem of calculus. Wallis generalized Cavalieris method, computing integrals of x to a power, including negative powers. The major advance in integration came in the 17th century with the independent discovery of the theorem of calculus by Newton. The theorem demonstrates a connection between integration and differentiation and this connection, combined with the comparative ease of differentiation, can be exploited to calculate integrals. In particular, the theorem of calculus allows one to solve a much broader class of problems. Equal in importance is the mathematical framework that both Newton and Leibniz developed
31.
Coherence (units of measurement)
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The concept of coherence was developed in the mid-nineteenth century by, amongst others, Kelvin and James Clerk Maxwell and promoted by the British Association for the Advancement of Science. The concept was applied to the centimetre–gram–second and the foot–pound–second systems of units in 1873 and 1875 respectively. The International System of Units was designed around the system of coherence, in SI, which is a coherent system, the unit of power is the watt which is defined as one joule per second. The earliest units of measure devised by humanity bore no relationship to each other, apart from Ancient China where the units of capacity and of mass are linked to red millet seed, there is little evidence of the linking of different quantities until the Age of Reason. The history of the measurement of length dates back to the early civilisations of the Middle East, archeologists have been able to reconstruct the units of measure in use in Mesopotamia, India, the Jewish culture and many others. Archaeological and other shows that in many civilisations, the ratios between different units for the same quantity of measure were adjusted so that they were integer numbers. In many early cultures such as Ancient Egypt, multiples of 2,3 and 5 were not always used—the Egyptian royal cubit being 28 fingers of 7 hands, non-commensurable quantities have different physical dimensions which means that adding or subtracting them is not meaningful. For instance, adding the mass of an object to its volume has no physical meaning, however, new quantities can be derived via multiplication and exponentiation of other units. As an example, the SI unit for force is the newton, note that coherence of a given unit depends on the definition of the base units. Should the meters definition change such that it is shorter by a factor of 100000, however, a coherent unit remains coherent if the base units are redefined in terms of other units with the numerical factor always being unity.001 m3 and the are was 100 m2. By contrast, coherence was an aim of the SI. Isaac Asimov wrote, In the cgs system, a force is described as one that will produce an acceleration of 1 cm/sec2 on a mass of 1 gm. A unit force is therefore 1 cm/sec2 multiplied by 1 gm, the first is a definition, the second is not. The first implies that the constant of proportionality in the law has a magnitude of one. Asimov uses them both together to prove that it is the number one. Asimovs conclusion is not the only possible one, in a system that uses the units foot for length, second for time, pound for mass, and pound-force for force, the law relating force, mass, and acceleration is F =0.031081 ma. Since the proportionality constant here is dimensionless and the units in any equation must balance without any numerical factor other than one and this conclusion appears paradoxical from the point of view of competing systems, according to which F = ma and 1 lbf =32.174 lb·ft/s2. A variant of this system applies the unit s2/ft to the proportionality constant and this has the effect of identifying the pound-force with the pound
32.
Electrochemical
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These reactions involve electric charges moving between electrodes and an electrolyte. Thus electrochemistry deals with the interaction between electrical energy and chemical change, chemical reactions where electrons are transferred directly between molecules and/or atoms are called oxidation-reduction or reactions. In general, electrochemistry describes the reactions when individual redox reactions are separate but connected by an external electric circuit. Understanding of electrical matters began in the sixteenth century, during this century, the English scientist William Gilbert spent 17 years experimenting with magnetism and, to a lesser extent, electricity. For his work on magnets, Gilbert became known as the Father of Magnetism and he discovered various methods for producing and strengthening magnets. In 1663, the German physicist Otto von Guericke created the first electric generator, the generator was made of a large sulfur ball cast inside a glass globe, mounted on a shaft. The ball was rotated by means of a crank and a spark was produced when a pad was rubbed against the ball as it rotated. The globe could be removed and used as source for experiments with electricity, by the mid—18th century the French chemist Charles François de Cisternay du Fay had discovered two types of static electricity, and that like charges repel each other whilst unlike charges attract. Du Fay announced that electricity consisted of two fluids, vitreous, or positive, electricity, and resinous, or negative, electricity and this was the two-fluid theory of electricity, which was to be opposed by Benjamin Franklins one-fluid theory later in the century. Galvani refuted this by obtaining muscular action with two pieces of the same material, in 1800, William Nicholson and Johann Wilhelm Ritter succeeded in decomposing water into hydrogen and oxygen by electrolysis. Soon thereafter Ritter discovered the process of electroplating and he also observed that the amount of metal deposited and the amount of oxygen produced during an electrolytic process depended on the distance between the electrodes. By 1801, Ritter observed thermoelectric currents and anticipated the discovery of thermoelectricity by Thomas Johann Seebeck, by the 1810s, William Hyde Wollaston made improvements to the galvanic cell. This work led directly to the isolation of sodium and potassium from their compounds, andré-Marie Ampère quickly repeated Ørsteds experiment, and formulated them mathematically. In 1821, Estonian-German physicist Thomas Johann Seebeck demonstrated the potential in the juncture points of two dissimilar metals when there is a heat difference between the joints. In 1827, the German scientist Georg Ohm expressed his law in this famous book Die galvanische Kette, in 1832, Michael Faradays experiments led him to state his two laws of electrochemistry. In 1836, John Daniell invented a primary cell which solved the problem of polarization by eliminating hydrogen gas generation at the positive electrode, later results revealed that alloying the amalgamated zinc with mercury would produce a higher voltage. William Grove produced the first fuel cell in 1839, in 1846, Wilhelm Weber developed the electrodynamometer. In 1868, Georges Leclanché patented a new cell which became the forerunner to the worlds first widely used battery
33.
Dimensional analysis
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Converting from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra. The concept of physical dimension was introduced by Joseph Fourier in 1822, Physical quantities that are measurable have the same dimension and can be directly compared to each other, even if they are originally expressed in differing units of measure. If physical quantities have different dimensions, they cannot be compared by similar units, hence, it is meaningless to ask whether a kilogram is greater than, equal to, or less than an hour. Any physically meaningful equation will have the dimensions on their left and right sides. Checking for dimensional homogeneity is an application of dimensional analysis. Dimensional analysis is routinely used as a check of the plausibility of derived equations and computations. It is generally used to categorize types of quantities and units based on their relationship to or dependence on other units. Many parameters and measurements in the sciences and engineering are expressed as a concrete number – a numerical quantity. Often a quantity is expressed in terms of other quantities, for example, speed is a combination of length and time. Compound relations with per are expressed with division, e. g.60 mi/1 h, other relations can involve multiplication, powers, or combinations thereof. A base unit is a unit that cannot be expressed as a combination of other units, for example, units for length and time are normally chosen as base units. Units for volume, however, can be factored into the units of length. Sometimes the names of units obscure that they are derived units, for example, an ampere is a unit of electric current, which is equivalent to electric charge per unit time and is measured in coulombs per second, so 1 A =1 C/s. Similarly, one newton is 1 kg⋅m/s2, percentages are dimensionless quantities, since they are ratios of two quantities with the same dimensions. In other words, the % sign can be read as 1/100, derivatives with respect to a quantity add the dimensions of the variable one is differentiating with respect to on the denominator. Thus, position has the dimension L, derivative of position with respect to time has dimension LT−1 – length from position, time from the derivative, the second derivative has dimension LT−2. In economics, one distinguishes between stocks and flows, a stock has units of units, while a flow is a derivative of a stock, in some contexts, dimensional quantities are expressed as dimensionless quantities or percentages by omitting some dimensions
34.
Werner Siemens
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Ernst Werner Siemens was a German inventor and industrialist. Siemens’s name has been adopted as the SI unit of electrical conductance and he was also the founder of the electrical and telecommunications company Siemens. He was a brother of Carl Heinrich von Siemens and Carl Wilhelm Siemens, sons of Christian Ferdinand Siemens, after finishing school, Siemens intended to study at the Bauakademie Berlin. Siemens was thought of as a soldier, receiving various medals, and inventing electrically-charged sea mines. Upon returning home from war, he put his mind to other uses and he is known world-wide for his advances in various technologies, and chose to work on perfecting technologies that had already been established. In 1843 he sold the rights to his first invention to Elkington of Birmingham, Siemens invented a telegraph that used a needle to point to the right letter, instead of using Morse code. Based on this invention, he founded the company Telegraphen-Bauanstalt von Siemens & Halske on 1 October 1847, the company was internationalised soon after its founding. One brother of Werner represented him in England and another in St. Petersburg, Russia, following his industrial career, he was ennobled in 1888, becoming Werner von Siemens. He retired from his company in 1890 and died in 1892 in Berlin, Siemens AG is one of the largest electrotechnological firms in the world. The von Siemens family still owns 6% of the shares and holds a seat on the supervisory board. Apart from the pointer telegraph Siemens made several contributions to the development of engineering and is therefore known as the founding father of the discipline in Germany. He built the worlds first electric elevator in 1880 and his company produced the tubes with which Wilhelm Conrad Röntgen investigated x-rays. He claimed invention of the dynamo although others invented it earlier, on 14 December 1877 he received German patent No.2355 for an electromechanical dynamic or moving-coil transducer, which was adapted by A. L. Thuras and E. C. Wente for the Bell System in the late 1920s for use as a loudspeaker, wentes adaptation was issued US patent 1,707,545 in 1929. Siemens is also the father of the trolleybus which he tried and tested with his Elektromote on 29 April 1882. He was married twice, first in 1852 to Mathilde Duman, patent 322,859 — Electric railway U. S. Patent 340,462 — Electric railway U. S, patent 415,577 — Electric meter U. S. Patent 428,290 — Electric meter U. S, patent 520,274 — Electric railway U. S. Werner von Siemens, Scientific & Technical Papers of Werner von Siemens
35.
Johann Christian Poggendorff
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Johann Christian Poggendorff, was a German physicist born in Hamburg. By far the greater and more important part of his work related to electricity, Poggendorff is known for his electrostatic motor which is analogous to Wilhelm Holtzs electrostatic machine. In 1841 he described the use of the potentiometer for measurement of electrical potentials without current draw, Poggendorf had apprenticed himself to an apothecary in Hamburg, and when twenty-two began to earn his living as an apothecarys assistant at Itzehoe. Ambition and an inclination towards a scientific career led him to throw up his business and move to Berlin. Here his abilities were recognized, and in 1823 he was appointed meteorological observer to the Academy of Sciences. He became editor of Annalen der Physik und Chemie, which was to be a continuation of Gilberts Annalen on an extended plan. Poggendorff was admirably qualified for the post, and edited the journal for 52 years, in 1826, Poggendorff developed the mirror galvanometer, a device for detecting electric currents. He was thus able to throw himself into the spirit of experimental science. He possessed in abundant measure the German virtue of orderliness in the arrangement of knowledge, further he had an engaging geniality of manner and much tact in dealing with men. These qualities soon made Poggendorffs Annalen the foremost scientific journal in Europe, in the course of his fifty-two years editorship of the Annalen Poggendorff could not fail to acquire an unusual acquaintance with the labors of modern men of science. This work contains a collection of facts invaluable to the scientific biographer. The first two volumes were published in 1863, after his death a volume appeared in 1898, covering the period 1858-1883. His literary and scientific reputation speedily brought him honorable recognition, in 1830 he was made royal professor, in 1838 Hon. Ph. D. and extraordinary professor in the University of Berlin, and in 1839 member of the Berlin Academy of Sciences. In 1845, he was elected a member of the Royal Swedish Academy of Sciences. Many offers of ordinary professorships were made to him, but he declined them all, devoting himself to his duties as editor of the Annalen and he died at Berlin on 24 January 1877. His daughter Marie Poggendorff married Valentin Rose in 1872, the Poggendorff Illusion is an optical illusion that involves the brains perception of the interaction between diagonal lines and horizontal and vertical edges. It is named after Poggendorff, who discovered it in the drawing of Johann Karl Friedrich Zöllner, in the adjacent picture, a straight black line is obscured by a dark gray rectangle. The black line appears disjointed, although it is in fact straight,2, Vol.139, pp 513–546 J. C
36.
Siemens mercury unit
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The Siemens mercury unit is an obsolete unit of electrical resistance. It was defined by Werner von Siemens in 1860 as the resistance of a column with a length of one metre. It is equivalent to approximately 0.953 ohm, glass tube cross sections are typically irregularly conical rather than perfect cylinders, which presented a problem in constructing precise measuring devices. The tube can then be used for measurement by applying a formula obtained from measurements that corrects for its conical shape. In 1881, a unit, the siemens, was formally defined by the metric system as the unit of electric conductivity. The Siemens mercury unit was superseded in 1884, but stayed in use in telegraph, international System of Units Units named after Siemens
37.
Metrology
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The field of metrology is important for establishing a common understanding of units, which is crucial in linking human activities. This led to the creation of the decimal based metric system in 1795 to establish a set of standards for types of measurements. This has since evolved into the International System of Units as a result of a made in the 11th Conference Generale des Poids et Mesures in 1960. The NMS greatly effects how measurements are undertaken in the country and this has wide reaching impacts in a variety of different regions of society. It has implications in the area of economies, energy, environment, health, manufacturing, industry, consumer confidence, the effects of metrology on trade and the economy are some of the easiest observed societal impacts. The field of metrology is important for establishing a common understanding of units and these base concepts of metrology are propagated by the three main fields of metrology, which are, scientific or fundamental metrology, applied, technical or industrial metrology, and legal metrology. While there is no definition of fundamental metrology it is considered to be the top level of scientific metrology that strives for the highest level of accuracy. The BIPM maintains a database of the calibration and measurement capabilities of various institutes around the world. These institutes, whose activities are peer-reviewed, provide the reference points for metrological traceability. In the area of measurement, the BIPM has identified nine metrology areas, including length, mass, although the emphasis in this area of metrology is on the measurements themselves, traceability of the calibration of the measurement devices is necessary to ensure confidence in the measurements. Industrial metrology is important to the economical and industrial development of a country, such statutory requirements might arise from, amongst others, the needs for protection of health, public safety, the environment, enabling taxation, protection of consumers and fair trade. The International Organization for Legal Metrology was established to assist in harmonising such regulations across national boundaries to ensure that legal requirements do not inhibit trade. In Europe WELMEC was established in 1990 to promote cooperation on the field of metrology in the European Union. Throughout history the ability to make measurements has been instrumental in the progress of mankind, the ability to measure alone is not sufficient, rather the ability to compare separate measurements and have agreeability is crucial for the measurements to be meaningful. The first record of a permanent standard is from 2900 BC, the cubit was decreed to be the length of the Pharaohs forearm plus the width of his hand and replica standards were given out to builders. The success of standardized length during the building of the pyramids is evidenced by the lengths of the pyramid bases differing by no more than 0. 05%, other civilizations produced their own measurement standards that were accepted throughout their nations. The architecture of the Roman and Greek empires were based on their own systems of measurement. Nonetheless, the fall of great empires and the rise of the Dark Ages caused much of measurement knowledge
38.
Josiah Latimer Clark
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Josiah Latimer Clark FRAS, was an English electrical engineer, born in Great Marlow, Buckinghamshire. Josiah Latimer Clark was born in Great Marlow, Buckinghamshire, and was brother to Edwin Clark. Latimer Clark studied chemistry at school and his first job was a large Dublin chemical manufacturing establishment. In 1848 he started to work in his brother Edwins civil engineering practice, two years later, when his brother was appointed Engineer to the Electric Telegraph Company, he again acted as his assistant, and subsequently succeeded him as Chief Engineer. He was President of the Society of Telegraph Engineers in 1875 when Ronalds’ renowned electrical library was gifted to the new Society, with Bright also he devised improvements in the insulation of submarine cables. In the later part of his life he was a member of several firms engaged in laying submarine cables, in manufacturing electrical appliances, Clark was one of the first authors to attach the metric prefixes mega- and micro- to units other than the metre. Clark died in London on the 30 October 1898, in 1854 Clark married Margaret Helen Preece, sister of Sir William Preece. Besides professional papers, Clark published an Elementary Treatise on Electrical Measurement and this article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. Clark, Josiah Latimer
39.
Charles Tilston Bright
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Sir Charles Tilston Bright was a British electrical engineer who oversaw the laying of the first transatlantic telegraph cable in 1858, for which work he was knighted. Born on 8 June 1832 in Wanstead, Essex, Bright was educated at Merchant Taylors School, at fifteen he became a clerk for the Electric Telegraph Company and as his talent for electrical engineering became evident, he was appointed engineer to the Magnetic Telegraph Company in 1852. In that role he supervised the laying of lines in the British Isles and this work, and the successful laying of other submarine cables, suggested to others that it might be possible to lay a cable across the Atlantic from Ireland to North America. Samuel Canning supported the effort on board HMS Agamemnon, Bright was knighted in Dublin just a few days later. Sir Charles Bright emerged from the debacle with his reputation intact and went on to supervise the laying of successful cables in the Mediterranean, the Persian Gulf. Bright formed a partnership with Josiah Latimer Clark in 1861 and together they introduced numerous improvements in the manufacture, testing, in 1865 he was awarded a Telford Medal for a paper on the possibilities of submarine cable telegraphy from England to China and Australia. From 1865 to 1868 Bright was Liberal MP for Greenwich and in 1887 he was elected president of the Society of Telegraph Engineers, Bright died on 3 May 1888, at Abbey Wood, near London. His son Charles Bright was also a noted engineer and historian of the subject. Charles Tilston Brights son, also Charles Bright, followed in his fathers footsteps, in addition to cable engineering he was a pioneer in the use of radio as a communication device on both ships and planes. He was elected a Fellow of the Royal Society of Edinburgh in 1895, Charles Bright Leigh Rayments Historical List of MPs Notes Hansard 1803–2005, contributions in Parliament by Charles Tilston Bright Hounslow Guardian article
40.
James Clerk Maxwell
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James Clerk Maxwell FRS FRSE was a Scottish scientist in the field of mathematical physics. Maxwells equations for electromagnetism have been called the great unification in physics after the first one realised by Isaac Newton. With the publication of A Dynamical Theory of the Electromagnetic Field in 1865, Maxwell proposed that light is an undulation in the same medium that is the cause of electric and magnetic phenomena. The unification of light and electrical phenomena led to the prediction of the existence of radio waves, Maxwell helped develop the Maxwell–Boltzmann distribution, a statistical means of describing aspects of the kinetic theory of gases. He is also known for presenting the first durable colour photograph in 1861 and his discoveries helped usher in the era of modern physics, laying the foundation for such fields as special relativity and quantum mechanics. Many physicists regard Maxwell as the 19th-century scientist having the greatest influence on 20th-century physics and his contributions to the science are considered by many to be of the same magnitude as those of Isaac Newton and Albert Einstein. In the millennium poll—a survey of the 100 most prominent physicists—Maxwell was voted the third greatest physicist of all time, behind only Newton and Einstein. On the centenary of Maxwells birthday, Einstein described Maxwells work as the most profound and the most fruitful that physics has experienced since the time of Newton. James Clerk Maxwell was born on 13 June 1831 at 14 India Street, Edinburgh, to John Clerk Maxwell of Middlebie, an advocate and his father was a man of comfortable means of the Clerk family of Penicuik, holders of the baronetcy of Clerk of Penicuik. His fathers brother was the 6th Baronet, James was the first cousin of the artist Jemima Blackburn and cousin of the civil engineer William Dyce Cay. They were close friends and Cay acted as his best man when Maxwell married, Maxwells parents met and married when they were well into their thirties, his mother was nearly 40 when he was born. They had had one child, a daughter named Elizabeth. When Maxwell was young his family moved to Glenlair House, which his parents had built on the 1,500 acres Middlebie estate, all indications suggest that Maxwell had maintained an unquenchable curiosity from an early age. By the age of three, everything moved, shone, or made a noise drew the question, whats the go o that. And show me how it doos is never out of his mouth and he also investigates the hidden course of streams and bell-wires, the way the water gets from the pond through the wall. Recognising the potential of the boy, Maxwells mother Frances took responsibility for Jamess early education. At eight he could recite long passages of Milton and the whole of the 119th psalm, indeed, his knowledge of scripture was already very detailed, he could give chapter and verse for almost any quotation from the psalms. His mother was ill with abdominal cancer and, after an unsuccessful operation
41.
William Thomson, 1st Baron Kelvin
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William Thomson, 1st Baron Kelvin, OM, GCVO, PC, FRS, FRSE was a Scots-Irish mathematical physicist and engineer who was born in Belfast in 1824. He worked closely with mathematics professor Hugh Blackburn in his work and he also had a career as an electric telegraph engineer and inventor, which propelled him into the public eye and ensured his wealth, fame and honour. For his work on the telegraph project he was knighted in 1866 by Queen Victoria. He had extensive maritime interests and was most noted for his work on the mariners compass, absolute temperatures are stated in units of kelvin in his honour. He was ennobled in 1892 in recognition of his achievements in thermodynamics and he was the first British scientist to be elevated to the House of Lords. The title refers to the River Kelvin, which close by his laboratory at the University of Glasgow. His home was the red sandstone mansion Netherhall, in Largs. William Thomsons father, James Thomson, was a teacher of mathematics and engineering at Royal Belfast Academical Institution, James Thomson married Margaret Gardner in 1817 and, of their children, four boys and two girls survived infancy. Margaret Thomson died in 1830 when William was six years old, William and his elder brother James were tutored at home by their father while the younger boys were tutored by their elder sisters. James was intended to benefit from the share of his fathers encouragement, affection. In 1832, his father was appointed professor of mathematics at Glasgow, the Thomson children were introduced to a broader cosmopolitan experience than their fathers rural upbringing, spending mid-1839 in London and the boys were tutored in French in Paris. Mid-1840 was spent in Germany and the Netherlands, language study was given a high priority. His sister, Anna Thomson, was the mother of James Thomson Bottomley FRSE, Thomson had heart problems and nearly died when he was 9 years old. In school, Thomson showed a keen interest in the classics along with his natural interest in the sciences, at the age of 12 he won a prize for translating Lucian of Samosatas Dialogues of the Gods from Latin to English. In the academic year 1839/1840, Thomson won the prize in astronomy for his Essay on the figure of the Earth which showed an early facility for mathematical analysis. Throughout his life, he would work on the problems raised in the essay as a strategy during times of personal stress. On the title page of this essay Thomson wrote the lines from Alexander Popes Essay on Man. These lines inspired Thomson to understand the world using the power and method of science, Go
42.
British Science Association
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The British Science Association is a charity and learned society founded in 1831 to aid in the promotion and development of science. Until 2009 it was known as the British Association for the Advancement of Science, the Association was founded in 1831 and modelled on the German Gesellschaft Deutscher Naturforscher und Ärzte. The prime mover was Reverend William Vernon Harcourt, following a suggestion by Sir David Brewster, Brewster, Charles Babbage, William Whewell and J. F. W. Johnston are also considered to be founding members. The first meeting was held in York on Tuesday 27 September 1831 with various scientific papers being presented on the following days and it was chaired by Viscount Milton, President of the Yorkshire Philosophical Society, and upwards of 300 gentlemen attended the meeting. The newspaper published the names of over a hundred of those attending, from that date onwards a meeting was held annually at a place chosen at a previous meeting. In 1832, for example, the meeting was held in Oxford, by this stage the Association had four sections, Physics, Chemistry, Geology and Natural History. A very important decision in the Association’s history was made in 1842 when it was resolved to create a “physical observatory”, a building that became well known as the Kew Observatory was taken on for the purpose and Francis Ronalds was chosen as the inaugural Honorary Director. Kew Observatory quickly became one of the most renowned meteorological and geomagnetic observatories in the world, one of the most famous events linked to the Association Meeting was an exchange between Thomas Henry Huxley and Bishop Samuel Wilberforce in 1860. Although a number of newspapers made passing references to the exchange, a need for standards arose with the submarine telegraph industry. The undertaking was suggested to the BA by William Thomson, josiah Latimer Clark and Fleeming Jenkin made preparations. Thomson, with his students, found that copper, contaminated with arsenic. The chemist Augustus Matthiessen contributed an appendix to the final 1873 report that showed temperature-dependence of alloys, the Association introduced the British Association screw threads, a series of screw thread standards in sizes from 0. 25mm up to 6mm, in 1884. The standards were ahead of their time in that they were based on the metric system and they remained in general use for instruments and small assemblies until metrication in the 1970s. A decision that became notorious in the century was made in 1878 when a committee of the Association recommended against constructing Charles Babbages analytical engine. The Association was parodied by English novelist Charles Dickens as The Mudfog Society for the Advancement of Everything in The Mudfog Papers, the Associations main aim is to improve the perception of science and scientists in the UK. Prof Sir George Porter, on becoming President in September 1985, was scathing against so-called soft sciences such as psychology and he claimed this was damaging the public perception of science. We run the risk of doing neither well, universities are underfunded, and must not be seen simply as a substitute for National Service to keep youngsters off the dole queue. He also said scientists have to be careful and consider the implications of what they are seeking to achieve