1.
Electric charge
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Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of charges, positive and negative. Like charges repel and unlike attract, an absence of net charge is referred to as neutral. An object is charged if it has an excess of electrons. The SI derived unit of charge is the coulomb. In electrical engineering, it is common to use the ampere-hour. The symbol Q often denotes charge, early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that dont require consideration of quantum effects. The electric charge is a conserved property of some subatomic particles. Electrically charged matter is influenced by, and produces, electromagnetic fields, the interaction between a moving charge and an electromagnetic field is the source of the electromagnetic force, which is one of the four fundamental forces. 602×10−19 coulombs. The proton has a charge of +e, and the electron has a charge of −e, the study of charged particles, and how their interactions are mediated by photons, is called quantum electrodynamics. Charge is the property of forms of matter that exhibit electrostatic attraction or repulsion in the presence of other matter. Electric charge is a property of many subatomic particles. The charges of free-standing particles are integer multiples of the charge e. Michael Faraday, in his electrolysis experiments, was the first to note the discrete nature of electric charge, robert Millikans oil drop experiment demonstrated this fact directly, and measured the elementary charge. By convention, the charge of an electron is −1, while that of a proton is +1, charged particles whose charges have the same sign repel one another, and particles whose charges have different signs attract. The charge of an antiparticle equals that of the corresponding particle, quarks have fractional charges of either −1/3 or +2/3, but free-standing quarks have never been observed. The electric charge of an object is the sum of the electric charges of the particles that make it up. An ion is an atom that has lost one or more electrons, giving it a net charge, or that has gained one or more electrons
2.
Electrical conductor
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In physics and electrical engineering, a conductor is an object or type of material that allows the flow of an electrical current in one or more directions. Materials made of metal are common electrical conductors, Electrical current is generated by the flow of negatively charged electrons, positively charged holes, and positive or negative ions in some cases. In order for current to flow, it is not necessary for one charged particle to travel from the producing the current to that consuming it. Instead, the particle simply needs to nudge its neighbor a finite amount who will nudge its neighbor and on and on until a particle is nudged into the consumer. Essentially what is occurring here is a chain of momentum transfer between mobile charge carriers, the Drude model of conduction describes this process more rigorously. Insulators are non-conducting materials with few mobile charges that support only insignificant electric currents, the resistance of a given conductor depends on the material it is made of, and on its dimensions. For a given material, the resistance is proportional to the cross-sectional area. For example, a copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a material, the resistance is proportional to the length, for example. The resistance R and conductance G of a conductor of uniform cross section, therefore, the resistivity and conductivity are proportionality constants, and therefore depend only on the material the wire is made of, not the geometry of the wire. Resistivity and conductivity are reciprocals, ρ =1 / σ, resistivity is a measure of the materials ability to oppose electric current. This formula is not exact, It assumes the current density is uniform in the conductor. However, this still provides a good approximation for long thin conductors such as wires. Another situation this formula is not exact for is with alternating current, then, the geometrical cross-section is different from the effective cross-section in which current actually flows, so the resistance is higher than expected. Similarly, if two conductors are each other carrying AC current, their resistances increase due to the proximity effect. Aside from the geometry of the wire, temperature also has a significant effect on the efficacy of conductors, temperature affects conductors in two main ways, the first is that materials may expand under the application of heat. The amount that the material will expand is governed by the expansion coefficient specific to the material. Such an expansion will change the geometry of the conductor and therefore its characteristic resistance, however, this effect is generally small, on the order of 10−6
3.
Capacitor
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A capacitor is a passive two-terminal electrical component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance, a capacitor was therefore historically first known as an electric condenser. The physical form and construction of practical capacitors vary widely and many types are in common use. Most capacitors contain at least two electrical conductors often in the form of plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, the nonconducting dielectric acts to increase the capacitors charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. No current actually flows through the dielectric, instead, the effect is a displacement of charges through the source circuit, if the condition is maintained sufficiently long, this displacement current through the battery ceases. However, if a voltage is applied across the leads of the capacitor. Capacitance is defined as the ratio of the charge on each conductor to the potential difference between them. The unit of capacitance in the International System of Units is the farad, capacitance values of typical capacitors for use in general electronics range from about 1 pF to about 1 mF. The capacitance of a capacitor is proportional to the area of the plates. In practice, the dielectric between the plates passes a small amount of leakage current and it has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance, Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies, in resonant circuits they tune radios to particular frequencies. In electric power systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in digital computers. Von Kleists hand and the water acted as conductors, and the jar as a dielectric, von Kleist found that touching the wire resulted in a powerful spark, much more painful than that obtained from an electrostatic machine
4.
Pieter van Musschenbroek
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Pieter van Musschenbroek was a Dutch scientist. He was a professor in Duisburg, Utrecht, and Leiden, where he held positions in mathematics, philosophy, medicine and he is credited with the invention of the first capacitor in 1746, the Leyden jar. He performed pioneering work on the buckling of compressed struts, Musschenbroek was also one of the first scientists to provide detailed descriptions of testing machines for tension, compression, and flexure testing. An early example of a problem in dynamic plasticity was described in the 1739 paper, pieter van Musschenbroek was born on 14 March 1692 in Leiden, Holland, Dutch Republic. His father was Johannes van Musschenbroek and his mother was Margaretha van Straaten, the Van Musschenbroeks, originally from Flanders, lived in the city of Leiden since circa 1600. His father was an instrument maker, who made instruments such as air pumps, microscopes. Van Musschenbroek attended Latin school until 1708, where he studied Greek, Latin, French, English, High German, Italian and he studied medicine at Leiden University and received his doctorate in 1715. He also attended lectures by John Theophilus Desaguliers and Isaac Newton in London and he finished his study in philosophy in 1719. Musschenbroek belonged to the tradition of Dutch thinkers who popularized the ontological argument of Gods design and he is author of Oratio de sapientia divina. In 1719, he became professor of mathematics and philosophy at the University of Duisburg, in 1721, he also became professor of medicine. In 1723, he left his posts in Duisburg and became professor at the University of Utrecht, in 1726 he also became professor in astronomy. Musschenbroeks Elementa Physica played an important part in the transmission of Isaac Newtons ideas in physics to Europe, in November 1734 he was elected a Fellow of the Royal Society. In 1739, he returned to Leiden, where he succeeded Jacobus Wittichius as professor, already during his studies at Leiden University Van Musschenbroek became interested in electrostatics. At that time, transient electrical energy could be generated by friction machines, Musschenbroek and his student Andreas Cunaeus discovered that the energy could be stored, in work that also involved Jean-Nicolas-Sébastien Allamand as collaborator. Van Musschenbroek communicated this discovery to René Réaumur in January 1746, and it was Abbé Nollet, the translator of Musschenbroeks letter from Latin, who named the invention the Leyden jar. Soon afterwards, it transpired that a German scientist, Ewald von Kleist, had constructed a similar device in late 1745. In 1754, he became a professor at the Imperial Academy of Science in Saint Petersburg. He was also elected a member of the Royal Swedish Academy of Sciences in 1747
5.
Leiden
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Leiden is a city and municipality in the Dutch province of South Holland. Leiden is located on the Oude Rijn, at a distance of some 20 kilometres from The Hague to its south, the recreational area of the Kaag Lakes lies just to the northeast of Leiden. A university city since 1575, Leiden houses Leiden University, the oldest university of the Netherlands, Leiden is a city with a rich cultural heritage, not only in science, but also in the arts. One of the worlds most famous painters, Rembrandt, was born, other famous Leiden painters include Lucas van Leyden, Jan van Goyen and Jan van Steen. The city has one of Europes most prominent scientific centres for more than four centuries. Modern scientific medical research and teaching started in the early 18th century in Leiden with Boerhaave, many important scientific discoveries have been made here, giving rise to Leiden’s motto, ‘City of Discoveries’. It is twinned with Oxford, the location of the United Kingdoms oldest university, Leiden University and Leiden University of Applied Sciences together have around 35,000 students. Leiden is a university city, university buildings are scattered throughout the city. Leiden was formed on a hill at the confluence of the rivers Oude. In the oldest reference to this, from circa 860, the settlement was called Leithon, the name is said to be from Germanic *leitha- canal. Leiden has in the past erroneously been associated with the Roman outpost Lugdunum Batavorum and this particular castellum was thought to be located at the Burcht of Leiden, and the citys name was thought to be derived of the Latin name Lugdunum. However the castellum was in closer to the town of Katwijk. The landlord of Leiden, situated in a stronghold on the hill, was subject to the Bishop of Utrecht. This county got its name in 1101 from a domain near the stronghold, Leiden was sacked in 1047 by Emperor Henry III. Early 13th century, Ada, Countess of Holland took refuge here when she was fighting in a war against her uncle, William I. He besieged the stronghold and captured Ada, Leiden received city rights in 1266. In 1389, its population had grown to about 4,000 persons, burgrave Filips of Wassenaar and the other local noblemen of the Hook faction assumed that the duke would besiege Leiden first and send small units out to conquer the surrounding citadels. But John of Bavaria chose to attack the citadels first and he rolled the cannons with his army but one which was too heavy went by ship
6.
Electrostatics
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Electrostatics is a branch of physics that deals with the phenomena and properties of stationary or slow-moving electric charges. Since classical physics, it has known that some materials such as amber attract lightweight particles after rubbing. The Greek word for amber, ήλεκτρον, or electron, was the source of the word electricity, Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulombs law, Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. This is because the charges that transfer are trapped there for a long enough for their effects to be observed. We begin with the magnitude of the force between two point charges q and Q. It is convenient to one of these charges, q, as a test charge. As we develop the theory, more source charges will be added.854187817 ×10 −12 C2 N −1 m −2, the SI units of ε0 are equivalently A2s4 kg−1m−3 or C2N−1m−2 or F m−1. Coulombs constant is, k e ≈14 π ε0 ≈8.987551787 ×109 N m 2 C −2. A single proton has a charge of e, and the electron has a charge of −e and these physical constants are currently defined so that ε0 and k0 are exactly defined, and e is a measured quantity. Electric field lines are useful for visualizing the electric field, field lines begin on positive charge and terminate on negative charge. Electric field lines are parallel to the direction of the field. The electric field, E →, is a field that can be defined everywhere. It is convenient to place a hypothetical test charge at a point, by Coulombs Law, this test charge will experience a force that can be used to define the electric field as follow F → = q E →. For a single point charge at the origin, the magnitude of electric field is E = k e Q / R2. The fact that the force can be calculated by summing all the contributions due to individual source particles is an example of the superposition principle. If the charge is distributed over a surface or along a line, the Divergence Theorem allows Gausss Law to be written in differential form, ∇ → ⋅ E → = ρ ε0. Where ∇ → ⋅ is the divergence operator, the definition of electrostatic potential, combined with the differential form of Gausss law, provides a relationship between the potential Φ and the charge density ρ, ∇2 ϕ = − ρ ε0
7.
Electrostatic generator
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An electrostatic generator, or electrostatic machine, is an electromechanical generator that produces static electricity, or electricity at high voltage and low continuous current. Electrostatic generators operate by using manual power to mechanical work into electric energy. The charge is generated by one of two methods, either the effect or electrostatic induction. Electrostatic machines are used in science classrooms to safely demonstrate electrical forces. Electrostatic generators such as the Van de Graaff generator, and variations as the Pelletron, a primitive form of frictional machine was invented around 1663 by Otto von Guericke, using a sulphur globe that could be rotated and rubbed by hand. It may not actually have been rotated during use and was not intended to produce electricity, isaac Newton suggested the use of a glass globe instead of a sulphur one. Francis Hauksbee improved the design, with his frictional electrical machine that enabled a glass sphere to be rotated rapidly against a woollen cloth. Generators were further advanced when Prof. Georg Matthias Bose of Wittenberg added a collecting conductor. Bose was the first to employ the prime conductor in such machines, in 1746, William Watsons machine had a large wheel turning several glass globes, with a sword and a gun barrel suspended from silk cords for its prime conductors. Johann Heinrich Winckler, professor of physics at Leipzig, substituted a leather cushion for the hand, during 1746, Jan Ingenhousz invented electric machines made of plate glass. In 1768, Jesse Ramsden constructed a widely used version of an electrical generator. In 1783, Dutch scientist Martin van Marum of Haarlem designed a large electrostatic machine of high quality with glass disks 1.65 meters in diameter for his experiments. Capable of producing voltage with either polarity, it was built under his supervision by John Cuthbertson of Amsterdam the following year, the generator is currently on display at the Teylers Museum in Haarlem. In 1785, N. Rouland constructed a machine that rubbed two grounded tubes covered with hare fur. The Winter machine possessed higher efficiency than earlier friction machines, in the 1830s, Georg Ohm possessed a machine similar to the Van Marum machine for his research. In 1840, the Woodward machine was developed by improving the Ramsden machine, also in 1840, the Armstrong hydroelectric machine was developed, using steam as a charge carrier. The presence of charge imbalance means that the objects will exhibit attractive or repulsive forces. Rubbing two non-conductive objects generates a great amount of static electricity and this is not the result of friction, two non-conductive surfaces can become charged by just being placed one on top of the other
8.
Battery (electricity)
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An electric battery is a device consisting of one or more electrochemical cells with external connections provided to power electrical devices such as flashlights, smartphones, and electric cars. When a battery is supplying power, its positive terminal is the cathode. The terminal marked negative is the source of electrons that when connected to a circuit will flow. It is the movement of ions within the battery which allows current to flow out of the battery to perform work. Historically the term specifically referred to a device composed of multiple cells. Primary batteries are used once and discarded, the materials are irreversibly changed during discharge. Common examples are the battery used for flashlights and a multitude of portable electronic devices. Secondary batteries can be discharged and recharged multiple times using mains power from a wall socket, examples include the lead-acid batteries used in vehicles and lithium-ion batteries used for portable electronics such as laptops and smartphones. According to a 2005 estimate, the battery industry generates US$48 billion in sales each year. Batteries have much lower energy than common fuels such as gasoline. This is somewhat offset by the efficiency of electric motors in producing mechanical work. The usage of battery to describe a group of electrical devices dates to Benjamin Franklin, alessandro Volta built and described the first electrochemical battery, the voltaic pile, in 1800. This was a stack of copper and zinc plates, separated by brine-soaked paper disks, Volta did not understand that the voltage was due to chemical reactions. Although early batteries were of value for experimental purposes, in practice their voltages fluctuated. It consisted of a pot filled with a copper sulfate solution, in which was immersed an unglazed earthenware container filled with sulfuric acid. These wet cells used liquid electrolytes, which were prone to leakage and spillage if not handled correctly, many used glass jars to hold their components, which made them fragile and potentially dangerous. These characteristics made wet cells unsuitable for portable appliances, near the end of the nineteenth century, the invention of dry cell batteries, which replaced the liquid electrolyte with a paste, made portable electrical devices practical. Batteries convert chemical energy directly to electrical energy, a battery consists of some number of voltaic cells
9.
Museum Boerhaave
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Museum Boerhaave is a museum of the history of science and medicine, based in Leiden, Netherlands. The museum hosts a collection of scientific instruments from all disciplines, but mainly from medicine, physics. The museum is located in a building that was originally a convent in central Leiden and it includes a reconstructed traditional anatomical theatre. Boerhaave Museums history began in 1907, when a Historical Exhibition of Natural Science, the many objects in the exhibition came from all the learned corners of the country. It was a success and there were immediately calls to set up a permanent science history exhibit. In 1928 a foundation was initiated by physicist Claude August Crommelin, the sciences to be represented included, Astronomy, Physics, Chemistry, Botany, Zoology, Pharmacy, all medical sciences - including Physiology, Anatomy et cetera, and Mathematics. In 1931 the museum opened as The Dutch Historical Museum of the Natural Sciences, in 1947 the museum, which was in fact a private foundation, became formally a national museum. It was renamed to The Dutch National Museum for the History of the Natural Sciences, an advisory board was installed in which members of Dutch universities would take seat. It underlined the ambition to become a museum, not a museum solely connected to the Leiden University. The plan was to merge collections of all institutes in one museum. This location of the now houses the National Museum of Ethnology. To create better housing the former nunnery of Saint Cecilia was bought by the Government Buildings Agency and this historic building has had various functions over time. The building dates from the early 15th century, the building had become municipal property after the Protestant Reformation and shortly before 1600 was converted into a pest house and lunatic asylum. The Leiden Academic hospital was founded in this location between 1636 and 1639, in 1967, with the prospect of a new location the name of the Museum was changed to Museum Boerhaave. However, it more than twenty years before the museum finally moved. After extensive restoration and expansion, the building is in use as a museum since 1991, the Boerhaave Museum is running a project to document approx. 3000 objects in its online, with pictures and descriptions for every single object. In April 2010 the site featured over 1750 objects, ordered by room and this overview is in large part based on the museums online documentation
10.
Ancient Greece
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Ancient Greece was a civilization belonging to a period of Greek history from the Greek Dark Ages of the 12th-9th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and this was followed by the period of Classical Greece, an era that began with the Greco-Persian Wars, lasting from the 5th to 4th centuries BC. Due to the conquests by Alexander the Great of Macedonia, Hellenistic civilization flourished from Central Asia to the end of the Mediterranean Sea. Classical Greek culture, especially philosophy, had a influence on ancient Rome. For this reason Classical Greece is generally considered to be the culture which provided the foundation of modern Western culture and is considered the cradle of Western civilization. Classical Antiquity in the Mediterranean region is considered to have begun in the 8th century BC. Classical Antiquity in Greece is preceded by the Greek Dark Ages and this period is succeeded, around the 8th century BC, by the Orientalizing Period during which a strong influence of Syro-Hittite, Jewish, Assyrian, Phoenician and Egyptian cultures becomes apparent. The end of the Dark Ages is also dated to 776 BC. The Archaic period gives way to the Classical period around 500 BC, Ancient Periods Astronomical year numbering Dates are approximate, consult particular article for details The history of Greece during Classical Antiquity may be subdivided into five major periods. The earliest of these is the Archaic period, in which artists made larger free-standing sculptures in stiff, the Archaic period is often taken to end with the overthrow of the last tyrant of Athens and the start of Athenian Democracy in 508 BC. It was followed by the Classical period, characterized by a style which was considered by observers to be exemplary, i. e. classical, as shown in the Parthenon. This period saw the Greco-Persian Wars and the Rise of Macedon, following the Classical period was the Hellenistic period, during which Greek culture and power expanded into the Near and Middle East. This period begins with the death of Alexander and ends with the Roman conquest, Herodotus is widely known as the father of history, his Histories are eponymous of the entire field. Herodotus was succeeded by authors such as Thucydides, Xenophon, Demosthenes, Plato, most of these authors were either Athenian or pro-Athenian, which is why far more is known about the history and politics of Athens than those of many other cities. Their scope is limited by a focus on political, military and diplomatic history, ignoring economic. In the 8th century BC, Greece began to emerge from the Dark Ages which followed the fall of the Mycenaean civilization, literacy had been lost and Mycenaean script forgotten, but the Greeks adopted the Phoenician alphabet, modifying it to create the Greek alphabet. The Lelantine War is the earliest documented war of the ancient Greek period and it was fought between the important poleis of Chalcis and Eretria over the fertile Lelantine plain of Euboea. Both cities seem to have suffered a decline as result of the long war, a mercantile class arose in the first half of the 7th century BC, shown by the introduction of coinage in about 680 BC
11.
Amber
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Amber is fossilized tree resin, which has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects and it has also been used as a healing agent in folk medicine. There are five classes of amber, defined on the basis of their chemical constituents, because it originates as a soft, sticky tree resin, amber sometimes contains animal and plant material as inclusions. Amber occurring in coal seams is also called resinite, and the term ambrite is applied to that found specifically within New Zealand coal seams, the English word amber derives from Arabic ʿanbar عنبر via Middle Latin ambar and Middle French ambre. The word was adopted in Middle English in the 14th century as referring to what is now known as ambergris, in the Romance languages, the sense of the word had come to be extended to Baltic amber from as early as the late 13th century. At first called white or yellow amber, this meaning was adopted in English by the early 15th century, as the use of ambergris waned, this became the main sense of the word. The two substances conceivably became associated or confused because they both were washed up on beaches. Ambergris is less dense water and floats, whereas amber is too dense to float. The classical names for amber, Latin electrum and Ancient Greek ἤλεκτρον, are connected to a term ἠλέκτωρ meaning beaming Sun, according to myth, when Phaëton son of Helios was killed, his mourning sisters became poplar trees, and their tears became elektron, amber. Earlier Pliny says that an island of three days sail from the Scythian coast called Balcia by Xenophon of Lampsacus, author of a fanciful travel book in Greek, is called Basilia by Pytheas. It is generally understood to be the same as Abalus and it is assumed that there were well-established trade routes for amber connecting the Baltic with the Mediterranean. Pliny states explicitly that the Germans export amber to Pannonia, from where it was traded further abroad by the Veneti, the ancient Italic peoples of southern Italy were working amber, the most important examples are on display at the National Archaeological Museum of Siritide to Matera. Amber used in antiquity as at Mycenae and in the prehistory of the Mediterranean comes from deposits of Sicily. Besides the fanciful explanations according to which amber is produced by the Sun, Pliny cites opinions that are aware of its origin in tree resin. Amber is produced from a marrow discharged by trees belonging to the genus, like gum from the cherry. This is confirmed by the recorded Old High German glas and Old English glær for amber, in Middle Low German, amber was known as berne-, barn-, börnstēn. The Low German term became dominant also in High German by the 18th century, the Baltic Lithuanian term for amber is gintaras and Latvian dzintars. They, and the Slavic jantar or Hungarian gyanta, are thought to originate from Phoenician jainitar, Early in the nineteenth century, the first reports of amber from North America came from discoveries in New Jersey along Crosswicks Creek near Trenton, at Camden, and near Woodbury
12.
Triboelectric effect
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The triboelectric effect is a type of contact electrification in which certain materials become electrically charged after they come into frictional contact with a different material. Rubbing glass with fur, or a plastic comb through the hair, most everyday static electricity is triboelectric. The polarity and strength of the charges produced differ according to the materials, surface roughness, temperature, strain, the triboelectric effect is not very predictable, and only broad generalizations can be made. Amber, for example, can acquire a charge by contact. This property was first recorded by Thales of Miletus, the word electricity is derived from William Gilberts initial coinage, electra, which originates in the Greek word for amber, ēlektron. The prefix tribo- refers to ‘friction’, as in tribology, other examples of materials that can acquire a significant charge when rubbed together include glass rubbed with silk, and hard rubber rubbed with fur. Physical separation of materials that are adhered together results in friction between the materials, thus, a material can develop a positive or negative charge that dissipates after the materials separate. Johan Carl Wilcke published the first triboelectric series in a 1757 paper on static charges, materials are often listed in order of the polarity of charge separation when they are touched with another object. A material towards the bottom of the series, when touched to a material near the top of the series, the farther away two materials are from each other on the series, the greater the charge transferred. Materials near to other on the series may not exchange any charge. This can be caused by rubbing, by contaminants or oxides, lists vary somewhat as to the exact order of some materials, since the relative charge varies for nearby materials. From actual tests, there is little or no difference in charge affinity between metals, probably because the rapid motion of conduction electrons cancels such differences. Although the part tribo- comes from the Greek for rubbing, τρίβω, after coming into contact, a chemical bond is formed between parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. This is what creates the net imbalance between the objects. In addition, some materials may exchange ions of differing mobility, the triboelectric effect is related to friction only because they both involve adhesion. However, the effect is enhanced by rubbing the materials together, as they touch. Surface nano-effects are not well understood, and the atomic force microscope has enabled rapid progress in this field of physics, a person simply walking across a carpet may build up a potential of many thousands of volts, enough to cause a spark one centimeter long or more. Simply removing a nylon shirt or corset can also create sparks, car travel can lead to a build-up of charge on the driver and passengers due to friction between the drivers clothes and the leather or plastic furnishings inside the vehicle
13.
Dielectric
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A dielectric material is an electrical insulator that can be polarized by an applied electric field. Because of dielectric polarization, positive charges are displaced toward the field and this creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, the study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics, optics, solid-state physics, while the term insulator implies low electrical conduction, dielectric typically means materials with a high polarizability. The latter is expressed by a called the relative permittivity. The term insulator is generally used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material, a common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor. The polarization of the dielectric by the electric field increases the capacitors surface charge for the given electric field strength. The term dielectric was coined by William Whewell in response to a request from Michael Faraday, a perfect dielectric is a material with zero electrical conductivity, thus exhibiting only a displacement current, therefore it stores and returns electrical energy as if it were an ideal capacitor. The electric susceptibility χe of a material is a measure of how easily it polarizes in response to an electric field. This, in turn, determines the electric permittivity of the material and thus many other phenomena in that medium. The susceptibility of a medium is related to its relative permittivity εr by χ e = ε r −1, so in the case of a vacuum, χ e =0. The electric displacement D is related to the polarization density P by D = ε0 E + P = ε0 E = ε r ε0 E, in general, a material cannot polarize instantaneously in response to an applied field. The more general formulation as a function of time is P = ε0 ∫ − ∞ t χ e E d t ′ and that is, the polarization is a convolution of the electric field at previous times with time-dependent susceptibility given by χe. The upper limit of this integral can be extended to infinity as well if one defines χe =0 for Δt <0, an instantaneous response corresponds to Dirac delta function susceptibility χe = χeδ. It is more convenient in a system to take the Fourier transform. Due to the theorem, the integral becomes a simple product. Note the simple frequency dependence of the susceptibility, or equivalently the permittivity, the shape of the susceptibility with respect to frequency characterizes the dispersion properties of the material. In the classical approach to the model, a material is made up of atoms
14.
Otto von Guericke
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Otto von Guericke was a German scientist, inventor, and politician. Otto von Guericke was born to a family of Magdeburg. In 1617 he became a student at the Leipzig University, owing to the outbreak of the Thirty Years War his studies at Leipzig were disrupted and subsequently he studied at the Academia Julia in Helmstedt and the universities of Jena and Leyden. At the last of these he attended courses on mathematics, physics and his education was completed by a nine-month-long trip to France and England. On his return to Magdeburg in 1626 he married Margarethe Alemann and he was to remain a member of this body until old age. Von Guericke was personally distrustful of the enthusiasm for the cause of Gustavus Adolphus but was nonetheless a victim of the fall of Magdeburg to von Tillys troops in May 1631. Following a period of employment as engineer in the service of Gustavus Adolphus he, for the next decade he was occupied rebuilding his own and the citys fortunes from the ruins of the fire of 1631. Diplomatic missions, often dangerous as well as tedious, occupied much of his time for the twenty years. A private scientific life, of which remains unclear, was developing in parallel. One of them, the Archbishop Elector Johann Philip von Schonborn, one of the professors at the College, Fr. Gaspar Schott, entered into correspondence with von Guericke and thus it was that, at the age of 55. Schott - Mechanica Hydraulico-pneumatica - published in 1657, the following year this was translated into Latin and, made aware of it in correspondence with Fr. Schott, von Guericke acquired a copy, in the decade following the first publication of his own work von Guericke, in addition to his diplomatic and administrative commitments, was scientifically very active. In the Preface to the Reader he claims to have finished the book on March 14,1663 though publication was delayed for nine years until 1672. In 1664, his work appeared in print, again through the good offices of Fr. Schott, the first section of whose book Technica Curiosa, entitled Mirabilia Magdeburgica, was dedicated to von Guerickes work, the earliest reference to the celebrated Magdeburg hemispheres experiment is on p.39 of the Technica Curiosa, where Fr. Schott notes that von Guericke had mentioned them in a letter of July 22,1656. Schott goes on to quote a subsequent letter of von Guericke of August 4,1657 in which he states that he now had carried out the experiment, at considerable cost, with 12 horses
15.
Sulfur
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Sulfur or sulphur is a chemical element with symbol S and atomic number 16. It is abundant, multivalent, and nonmetallic, under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for gold, platinum, iridium, tellurium, though sometimes found in pure, native form, sulfur usually occurs as sulfide and sulfate minerals. Being abundant in native form, sulfur was known in ancient times, being mentioned for its uses in ancient India, ancient Greece, China, in the Bible, sulfur is called brimstone. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from natural gas, the greatest commercial use of the element is the production of sulfuric acid for sulfate and phosphate fertilizers, and other chemical processes. The element sulfur is used in matches, insecticides, and fungicides, many sulfur compounds are odoriferous, and the smells of odorized natural gas, skunk scent, grapefruit, and garlic are due to organosulfur compounds. Hydrogen sulfide gives the characteristic odor to rotting eggs and other biological processes, sulfur is an essential element for all life, but almost always in the form of organosulfur compounds or metal sulfides. Three amino acids and two vitamins are organosulfur compounds, many cofactors also contain sulfur including glutathione and thioredoxin and iron–sulfur proteins. Disulfides, S–S bonds, confer mechanical strength and insolubility of the keratin, found in outer skin, hair. Sulfur is one of the chemical elements needed for biochemical functioning and is an elemental macronutrient for all organisms. Sulfur is derived from the Latin word sulpur, which was Hellenized to sulphur, the spelling sulfur appears toward the end of the Classical period. In 12th-century Anglo-French, it was sulfre, in the 14th century the Latin ph was restored, for sulphre, the parallel f~ph spellings continued in Britain until the 19th century, when the word was standardized as sulphur. Sulfur was the form chosen in the United States, whereas Canada uses both, the IUPAC adopted the spelling sulfur in 1990, as did the Nomenclature Committee of the Royal Society of Chemistry in 1992, restoring the spelling sulfur to Britain. Sulfur forms polyatomic molecules with different chemical formulas, the best-known allotrope being octasulfur, cyclo-S8. The point group of cyclo-S8 is D4d and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless and it melts at 115.21 °C, boils at 444.6 °C and sublimes easily. At 95.2 °C, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-polymorph, the structure of the S8 ring is virtually unchanged by this phase change, which affects the intermolecular interactions. At higher temperatures, the viscosity decreases as depolymerization occurs, molten sulfur assumes a dark red color above 200 °C
16.
Daniel Gralath
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Daniel Gralath was a physicist and a mayor of Danzig. Gralath was born in Danzig in Poland of a well-to-do trade family and he had studied law and philosophy in Halle, then in Leyden and Marburg from 1728 to 1734. Later he became councilman and, in 1763, mayor of Danzig and his father-in-law was Jacob Theodor Klein, a city secretary and also a very distinguished scientist, nicknamed Gedanensium Plinius. As a physicist, Gralath worked on electricity, founded the Danzig Research Society, Gralath improved the design and demonstrated its effects on a chain of 20 persons. He was also the first to combine several jars to make a battery, from 1747 to 1756, he published his History of Electricity with three volumes
17.
Jean-Antoine Nollet
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Jean-Antoine Nollet was a French clergyman and physicist. As a priest, he was known as Abbé Nollet. Nollet was particularly interested in the new science of electricity, which he explored with the help of Du Fay and he joined the Royal Society of London in 1734 and later became the first professor of experimental physics at the University of Paris. He is reputed to have given the name to the Leyden jar after it was invented by Pieter van Musschenbroek, in 1746 he gathered about two hundred monks into a circle about a mile in circumference, with pieces of iron wire connecting them. In 1748 he discovered the phenomenon of osmosis in natural membranes, in 1750 Nollet made some advances on electrospray. He noted water flowing from a vessel would aerosolize if the vessel was electrified and placed near electrical ground. He also noted that similarly “a person, electrified by connection to a generator, would not bleed normally if he were to cut himself, blood would spray from the wound. ”List of Roman Catholic scientist-clerics Biography by Eugenii Katz Herbermann, Charles. Partial translation of Observations sur quelques nouveaux phénomènes dÉlectricité, published in Mémoires de l Académie Royale des Sciences,1796, extract of the Observations Made in Italy, by the Abbe Nollet, F. R. S. on the Grotta de Cani. Translated from the French by Tho
18.
Royal Society
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Founded in November 1660, it was granted a royal charter by King Charles II as The Royal Society. The society is governed by its Council, which is chaired by the Societys President, according to a set of statutes and standing orders. The members of Council and the President are elected from and by its Fellows, the members of the society. As of 2016, there are about 1,600 fellows, allowed to use the postnominal title FRS, there are also royal fellows, honorary fellows and foreign members, the last of which are allowed to use the postnominal title ForMemRS. The Royal Society President is Venkatraman Ramakrishnan, who took up the post on 30 November 2015, since 1967, the society has been based at 6–9 Carlton House Terrace, a Grade I listed building in central London which was previously used by the Embassy of Germany, London. The Royal Society started from groups of physicians and natural philosophers, meeting at variety of locations and they were influenced by the new science, as promoted by Francis Bacon in his New Atlantis, from approximately 1645 onwards. A group known as The Philosophical Society of Oxford was run under a set of rules still retained by the Bodleian Library, after the English Restoration, there were regular meetings at Gresham College. It is widely held that these groups were the inspiration for the foundation of the Royal Society, I will not say, that Mr Oldenburg did rather inspire the French to follow the English, or, at least, did help them, and hinder us. But tis well known who were the men that began and promoted that design. This initial royal favour has continued and, since then, every monarch has been the patron of the society, the societys early meetings included experiments performed first by Hooke and then by Denis Papin, who was appointed in 1684. These experiments varied in their area, and were both important in some cases and trivial in others. The Society returned to Gresham in 1673, there had been an attempt in 1667 to establish a permanent college for the society. Michael Hunter argues that this was influenced by Solomons House in Bacons New Atlantis and, to a lesser extent, by J. V. The first proposal was given by John Evelyn to Robert Boyle in a letter dated 3 September 1659, he suggested a scheme, with apartments for members. The societys ideas were simpler and only included residences for a handful of staff and these plans were progressing by November 1667, but never came to anything, given the lack of contributions from members and the unrealised—perhaps unrealistic—aspirations of the society. During the 18th century, the gusto that had characterised the early years of the society faded, with a number of scientific greats compared to other periods. The pointed lightning conductor had been invented by Benjamin Franklin in 1749, during the same time period, it became customary to appoint society fellows to serve on government committees where science was concerned, something that still continues. The 18th century featured remedies to many of the early problems
19.
Series and parallel circuits
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Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur frequently, components connected in series are connected along a single path, so the same current flows through all of the components. Components connected in parallel are connected, so the voltage is applied to each component. A circuit composed solely of components connected in series is known as a circuit, likewise. In a series circuit, the current through each of the components is the same, in a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component. Consider a very simple circuit consisting of four light bulbs and one 6 V battery. If a wire joins the battery to one bulb, to the bulb, to the next bulb, to the next bulb, then back to the battery, in one continuous loop. If each bulb is wired to the battery in a separate loop, the bulbs are said to be in parallel. If the four light bulbs are connected in series, there is current through all of them, and the voltage drop is 1.5 V across each bulb. If the light bulbs are connected in parallel, the currents through the light bulbs combine to form the current in the battery, while the drop is across each bulb. In a series circuit, every device must function for the circuit to be complete, one bulb burning out in a series circuit breaks the circuit. In parallel circuits, each light has its own circuit, so all but one light could be burned out, Series circuits are sometimes called current-coupled or daisy chain-coupled. The current in a series circuit goes through every component in the circuit, therefore, all of the components in a series connection carry the same current. There is only one path in a circuit in which the current can flow. For example, if one of the light bulbs in an older-style string of Christmas tree lights burns out or is removed. = I n In a series circuit the current is the same for all of elements. The total resistance of resistors in series is equal to the sum of their individual resistances, R total = R1 + R2 + ⋯ + R n Electrical conductance presents a reciprocal quantity to resistance. Total conductance of a series circuits of pure resistors, therefore, for a special case of two resistors in series, the total conductance is equal to, G total = G1 G2 G1 + G2
20.
Benjamin Franklin
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Benjamin Franklin was one of the Founding Fathers of the United States. Franklin was a polymath and a leading author, printer, political theorist, politician, freemason, postmaster, scientist, inventor, civic activist, statesman. As a scientist, he was a figure in the American Enlightenment. As an inventor, he is known for the rod, bifocals. He facilitated many civic organizations, including Philadelphias fire department and the University of Pennsylvania, Franklin earned the title of The First American for his early and indefatigable campaigning for colonial unity, initially as an author and spokesman in London for several colonies. As the first United States Ambassador to France, he exemplified the emerging American nation, in the words of historian Henry Steele Commager, In a Franklin could be merged the virtues of Puritanism without its defects, the illumination of the Enlightenment without its heat. To Walter Isaacson, this makes Franklin the most accomplished American of his age, Franklin became a successful newspaper editor and printer in Philadelphia, the leading city in the colonies, publishing the Pennsylvania Gazette at the age of 23. He became wealthy publishing this and Poor Richards Almanack, which he authored under the pseudonym Richard Saunders, after 1767, he was associated with the Pennsylvania Chronicle, a newspaper that was known for its revolutionary sentiments and criticisms of the British policies. He pioneered and was first president of The Academy and College of Philadelphia which opened in 1751 and he organized and was the first secretary of the American Philosophical Society and was elected president in 1769. Franklin became a hero in America as an agent for several colonies when he spearheaded an effort in London to have the Parliament of Great Britain repeal the unpopular Stamp Act. An accomplished diplomat, he was widely admired among the French as American minister to Paris and was a figure in the development of positive Franco-American relations. His efforts proved vital for the American Revolution in securing shipments of crucial munitions from France, during the Revolution, he became the first US Postmaster General. He was active in community affairs and colonial and state politics, from 1785 to 1788, he served as governor of Pennsylvania. He initially owned and dealt in slaves but, by the 1750s, he argued against slavery from an economic perspective, Franklins father, Josiah Franklin, was a tallow chandler, a soap-maker and a candle-maker. Josiah was born at Ecton, Northamptonshire, England on December 23,1657, the son of Thomas Franklin, a blacksmith-farmer, and Jane White. His mother, Abiah Folger, was born in Nantucket, Massachusetts, on August 15,1667, to Peter Folger, a miller and schoolteacher, and his wife, Mary Morrill, Josiah Franklin had seventeen children with his two wives. He married his first wife, Anne Child, in about 1677 in Ecton and emigrated with her to Boston in 1683, after her death, Josiah was married to Abiah Folger on July 9,1689 in the Old South Meeting House by Samuel Willard. Benjamin, their child, was Josiah Franklins fifteenth child and tenth
21.
Cannon
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A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellants to launch a projectile, which may or may not be explosive. The word cannon is derived from languages, in which the original definition can usually be translated as tube, cane. The Greeks invented the first type—a steam cannon—designed by Archimedes during the Siege of Syracuse, ctesibius built a steam cannon in Alexandria and in the fifteenth century Leonardo da Vinci designed another, the Architonnerre, based on Archimedes work. The earliest form of artillery was developed in Song China, over time replacing siege engines. In the Middle East, the first use of the cannon is argued to be during the 1260 Battle of Ain Jalut between the Mamluk Sultanate and Mongol Empire. The first cannon in Europe were in use in the Iberian Peninsula by the mid-13th century and it was during this period, the Middle Ages, that cannon became standardised, and more effective in both the anti-infantry and siege roles. After the Middle Ages most large cannon were abandoned in favour of greater numbers of lighter, Cannon also transformed naval warfare in the early modern period, as European navies took advantage of their firepower. In World War I, the majority of fatalities were caused by artillery. Most modern cannon are similar to those used in the Second World War, Cannon was widely known as the earliest form of a gun and artillery, before early firearms were invented. The word has been used to refer to a gun since 1326 in Italy, both Cannons and Cannon are correct and in common usage, with one or the other having preference in different parts of the English-speaking world. Cannons is more common in North America and Australia, while cannon as plural is more common in the United Kingdom, Cannon in general have the form of a truncated cone with an internal cylindrical bore for holding an explosive charge and a projectile. The thickest, strongest, and closed part of the cone is located near the explosive charge, as any explosive charge will dissipate in all directions equally, the thickest portion of the cannon is useful for containing and directing this force. Field artillery cannon in Europe and the Americas were initially made most often of bronze, though later forms were constructed of cast iron and eventually steel. However, cast iron cannon have a tendency to burst without having any previous weakness or wear. The following terms refer to the components or aspects of a classical western cannon as illustrated here. In what follows, the words near, close, and behind will refer to those parts towards the thick, closed end of the piece, and far, front, in front of, and before to the thinner, open end. Bore, The hollow cylinder bored down the centre of the cannon, including the base of the bore or bottom of the bore, the diameter of the bore represents the cannons calibre. Chamber, The cylindrical, conical, or spherical recess at the nearest end of the bottom of the bore into which the gunpowder is packed
22.
Franz Aepinus
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Franz Ulrich Theodor Aepinus was a German and Russian Empire natural philosopher. Aepinus is best known for his researches, theoretical and experimental, in electricity and he was born at Rostock in the Duchy of Mecklenburg-Schwerin. He was descended from Johannes Aepinus, the first to adopt the Greek form of the family name Hugk or Huck, in 1755 he was briefly the director of the Astronomisches Rechen-Institut. In 1757 he settled in St Petersburg as member of the Russian Academy of Sciences and professor of physics, the rest of his life was spent at Dorpat. In 1761, Aepinus was elected a member of the Royal Swedish Academy of Sciences. In 1764, he was appointed as a head of the service of Russia. His principal work, Tentamen Theoriae Electricitatis et Magnetismi, published at St Petersburg in 1759, was the first systematic attempt to apply mathematical reasoning to these subjects. Aepinus and Henry Cavendish devised theories of electricity which were essentially the same, Aepinus however published his theory about ten years before that of Cavendish. These are essentially modern theories which eventually put to rest the idea of two fluids, the electric fluid is a substance, the particles of which repel each other, and attract the particles of all other matter, with a force inversely as the square of distance. The particles of all other matter also repel each other, Cavendish and Aepinus believed that the electric fluid was another sort of matter. In effect, they are imagining the electric fluid as consisting of electrons with almost no mass, static electricity then becomes a matter of a superabundance of electrons in one body, and a shortage of electrons in another. Electricity entry in Edinburgh Encyclopaedia of 1832 Heilbron, John L. Aepinus, essay on the Theory of Electricity and Magnetism by Roderick Weir Home. OConnor, John J. Robertson, Edmund F. Franz Aepinus, MacTutor History of Mathematics archive, University of St Andrews
23.
Johan Wilcke
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Johan Carl Wilcke was a Swedish physicist. Wilcke was born in Wismar, son of a clergyman who in 1739 was appointed pastor of the German Church in Stockholm. He went to the German school in Stockholm and enrolled at the University of Uppsala in 1749 and he spent the years from 1751 travelling abroad and received the magister degree from the University of Rostock in 1757, after having published the dissertation De electricitatibus contrariis. He became a professor in 1770, and permanent secretary of the Academy of Sciences in 1784. He died in Stockholm in 1796 and his two areas of significant research were electricity and caloric theory. In 1762 he invented a generator that was a first version of the electrophorus. In 1772 he calculated the latent heat of ice, in 1789 he was elected a Fellow of the Royal Society Svenskt biografiskt handlexikon, vol 2, p.732 Encyclopedia. com, Wilcke, Johan Carl Johan Carl Wilcke in Rostock Matrikelportal
24.
Spark-gap transmitter
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A spark-gap transmitter is a device that generates radio frequency electromagnetic waves using a spark gap. Spark gap transmitters were the first devices to demonstrate practical radio transmission, later, more efficient transmitters were developed based on rotary machines like the high-speed Alexanderson alternators and the static Poulsen Arc generators. Even when vacuum tube based transmitters had been installed, many retained their crude. However, by 1940, the technology was no longer used for communication, use of the spark-gap transmitter led to many radio operators being nicknamed Sparks long after they ceased using spark transmitters. Even today, the German verb funken, literally, to spark, the effects of sparks causing unexplained action at a distance, such as inducing sparks in nearby devices, had been noticed by scientists and experimenters well before the invention of radio. Extensive experiments were conducted by Joseph Henry, Thomas Edison and David Edward Hughes, with no other theory to explain the phenomenon, it was usually written off as electromagnetic induction. Hertz used a spark gap transmitter and a tuned spark gap detector located a few meters from the source. Many experimenters used the spark gap setup to further investigate the new Hertzian wave phenomenon, including Oliver Lodge, the Italian inventor Guglielmo Marconi used a spark-gap transmitter in his experiments to develop the radio phenomenon into a wireless telegraphy system in the early 1890s. In 1895 he succeeded in transmitting over a distance of 1 1/4 miles and his first transmitter consisted of an induction coil connected between a wire antenna and ground, with a spark gap across it. Every time the induction coil pulsed, the antenna was momentarily charged up to tens of thousands of volts until the gap started to arc. This acted as a switch, essentially connecting the antenna to ground. While the various systems of spark transmitters worked well enough to prove the concept of wireless telegraphy. The biggest problem was that the power that could be transmitted was directly determined by how much electrical charge the antenna could hold. Because the capacitance of practical antennas is quite small, the way to get a reasonable power output was to charge it up to very high voltages. However, this made transmission impossible in rainy or even damp conditions, also, it necessitated a quite wide spark gap, with a very high electrical resistance, with the result that most of the electrical energy was used simply to heat up the air in the spark gap. Another problem with the transmitter was a result of the shape of the waveform produced by each burst of electromagnetic radiation. These transmitters radiated an extremely dirty wide band signal that could interfere with transmissions on nearby frequencies. Receiving sets relatively close to such a transmitter had entire sections of a band masked by this wide band noise, reginald Fessendens first attempts to transmit voice employed a spark transmitter operating at approximately 10,000 sparks/second
25.
Inductance
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According to Lenzs law, a changing electric current through a circuit that contains inductance induces a proportional voltage, which opposes the change in current. The varying field in this circuit may also induce an EMF in neighbouring circuits, the term inductance was coined by Oliver Heaviside in 1886. It is customary to use the symbol L for inductance, in honour of the physicist Heinrich Lenz. In the SI system, the measurement unit for inductance is the henry, with the unit symbol H, named in honor of Joseph Henry, who discovered inductance independently of, an electronic component that is intended to add inductance to a circuit is called an inductor. Inductors are typically manufactured from coils of wire and this design delivers two desired properties, a concentration of the magnetic field into a small physical space and a linking of the magnetic field into the circuit multiple times. The relationship between the self-inductance, L, of a circuit, the voltage, v. A voltage is induced across an inductor, that is equal to the product of the inductors inductance, all circuits have, in practice, some inductance, which may have beneficial or detrimental effects. For a tuned circuit, inductance is used to provide a frequency-selective circuit, practical inductors may be used to provide filtering, or energy storage, in a given network. The inductance of long AC power transmission lines affects the power capacity of the line, sensitive circuits, such as microphone and computer network cables, may utilize special cabling construction, limiting the inductive coupling between circuits. The generalization to the case of K electrical circuits with currents, here, inductance L is a symmetric matrix. The diagonal coefficients Lm, m are called coefficients of self-inductance, the coefficients of inductance are constant, as long as no magnetizable material with nonlinear characteristics is involved. This is a consequence of the linearity of Maxwells equations in the fields. The coefficients of inductance become functions of the currents in the nonlinear case, the inductance equations above are a consequence of Maxwells equations. There is a derivation in the important case of electrical circuits consisting of thin wires. Here Nm denotes the number of turns in loop m, Φm, the flux through loop m. This equation follows from Amperes law - magnetic fields and fluxes are linear functions of the currents and this agrees with the definition of inductance above if the coefficients Lm, n are identified with the coefficients of inductance. Because the total currents Nnin contribute to Φm it also follows that Lm, ∑ n =1 K ∂ W ∂ i n d i n. This must agree with the change of the field energy, W
26.
Radio
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When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
27.
Glass
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Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, normally, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature. The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass, soda-lime glasses account for about 90% of manufactured glass. Most common glass contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths
28.
Electrode
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An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. The word was coined by William Whewell at the request of the scientist Michael Faraday from the Greek words elektron, meaning amber, and hodos, an electrode in an electrochemical cell is referred to as either an anode or a cathode. The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs, each electrode may become either the anode or the cathode depending on the direction of current through the cell. A bipolar electrode is an electrode that functions as the anode of one cell, a primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. The anode is always the negative electrode, the cell can be discharged but not recharged. A secondary cell, for example a rechargeable battery, is a cell in which the reactions are reversible. When the cell is being charged, the anode becomes the positive and this is also the case in an electrolytic cell. When the cell is being discharged, it behaves like a cell, with the anode as the negative. In a vacuum tube or a semiconductor having polarity the anode is the positive electrode, the electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e. g. base, gate, control grid. In a three-electrode cell, an electrode, also called an auxiliary electrode, is used only to make a connection to the electrolyte so that a current can be applied to the working electrode. The counter electrode is made of an inert material, such as a noble metal or graphite. In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. For a direct current system the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes, for an alternating current arc welder the welding electrode would not be considered an anode or cathode. Electrodes are used to provide current through nonmetal objects to them in numerous ways. These electrodes are used for advanced purposes in research and investigation
29.
Ground (electricity)
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Electrical circuits may be connected to ground for several reasons. In mains powered equipment, exposed parts are connected to ground to prevent user contact with dangerous voltage when electrical insulation fails. In electrical power systems, a protective ground conductor is an essential part of the safety Earthing system. Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices, in some telegraph and power transmission circuits, the earth itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor. For measurement purposes, the Earth serves as a constant potential reference against which other potentials can be measured, an electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a ground is usually idealized as a source or sink for charge. Where a real ground connection has a significant resistance, the approximation of zero potential is no longer valid, stray voltages or earth potential rise effects will occur, which may create noise in signals or if large enough will produce an electric shock hazard. This is usually a large conductor attached to one side of the power supply which serves as the return path for current from many different components in the circuit. Long-distance electromagnetic telegraph systems from 1820 onwards used two or more wires to carry the signal and return currents. During dry weather, the ground connection often developed a high resistance, an electrical connection to earth can be used as a reference potential for radio frequency signals for certain kinds of antennas. The part directly in contact with the earth - the earth electrode - can be as simple as a rod or stake driven into the earth. Because high frequency signals can flow to earth due to capacitative effects, because of this, a complex system of buried rods and wires can be effective. An ideal signal ground maintains a fixed potential regardless of how much current flows into ground or out of ground. Some types of transmitting antenna systems in the VLF, LF, MF, sometimes a counterpoise is used as a ground plane, supported above the ground. Electrical power distribution systems are connected to ground to limit the voltage that can appear on distribution circuits. A distribution system insulated from ground may attain a high potential due to transient voltages caused by arcing, static electricity, a ground connection of the system dissipates such potentials and limits the rise in voltage of the grounded system. In a mains electricity wiring installation, the ground conductor typically refers to three different conductors or conductor systems as listed below. Equipment earthing conductors provide a connection between non-current-carrying metallic parts of equipment and the earth
30.
William Watson (scientist)
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William Watson, FRS was an English physician and scientist who was born and died in London. His early work was in botany, and he helped to introduce the work of Carolus Linnaeus into England and he became a Fellow of the Royal Society in 1741 and vice president in 1772. In 1746, he showed that the capacity of the Leyden jar could be increased by coating it inside and he acknowledged that the same theory had been independently developed at the same time by Benjamin Franklin—the two men later became allies in both scientific and political matters. On 14 August 1747 he made an experiment to conduct electricity through a 6,732 foot long wire at Shooters Hill in London, at another experiment he made, the wire was 12,276 feet. Previous experiments in France had only tried shorter distances
31.
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
32.
Capacitance
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Capacitance is the ability of a body to store an electric charge. There are two related notions of capacitance--self capacitance and mutual capacitance--that are usually both designated by the same term, capacitance. Any object that can be electrically charged exhibits self capacitance, a material with a large self capacitance holds more electric charge at a given voltage, than one with low capacitance. The notion of mutual capacitance is important for understanding the operations of the capacitor. The capacitance is a function only of the geometry of the design, for many dielectric materials, the permittivity and thus the capacitance, is independent of the potential difference between the conductors and the total charge on them. The SI unit of capacitance is the farad, named after the English physicist Michael Faraday, a 1 farad capacitor, when charged with 1 coulomb of electrical charge, has a potential difference of 1 volt between its plates. In electrical circuits, the capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. It is actually mutual capacitance between the turns of the coil and is a form of stray, or parasitic capacitance. This self-capacitance is an important consideration at high frequencies and it changes the impedance of the coil and gives rise to parallel resonance. In many applications this is an effect and sets an upper frequency limit for the correct operation of the circuit. The inverse of capacitance is called elastance, the unit of elastance is the daraf, but is not recognised by SI. A common form is a capacitor, which consists of two conductive plates insulated from each other, usually sandwiching a dielectric material. In a parallel capacitor, capacitance is very nearly proportional to the surface area of the conductor plates. If the charges on the plates are +q and −q, and V gives the voltage between the plates, then the capacitance C is given by C = q V. which gives the voltage/current relationship I = C d V d t. Historically, a farad was regarded as a large unit. Its subdivisions were invariably used, namely the microfarad, nanofarad and picofarad, more recently, technology has advanced such that capacitors of 1 farad and greater can be constructed in a structure little larger than a coin battery. Such capacitors are used for energy storage replacing more traditional batteries. The energy stored in a capacitor is found by integrating the work W, W charging =12 C V2 The discussion above is limited to the case of two conducting plates, although of arbitrary size and shape
33.
Vacuum
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Vacuum is space void of matter. The word stems from the Latin adjective vacuus for vacant or void, an approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. In engineering and applied physics on the hand, vacuum refers to any space in which the pressure is lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum, the quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum, for example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth of atmospheric pressure, outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average. In the electromagnetism in the 19th century, vacuum was thought to be filled with a medium called aether, in modern particle physics, the vacuum state is considered the ground state of matter. Vacuum has been a frequent topic of debate since ancient Greek times. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other techniques were developed as a result of his theories of atmospheric pressure. A torricellian vacuum is created by filling a glass container closed at one end with mercury. Vacuum became an industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes. The recent development of human spaceflight has raised interest in the impact of vacuum on human health, the word vacuum comes from Latin an empty space, void, noun use of neuter of vacuus, meaning empty, related to vacare, meaning be empty. Vacuum is one of the few words in the English language that contains two consecutive letters u. Historically, there has been dispute over whether such a thing as a vacuum can exist. Ancient Greek philosophers debated the existence of a vacuum, or void, in the context of atomism, Aristotle believed that no void could occur naturally, because the denser surrounding material continuum would immediately fill any incipient rarity that might give rise to a void. Almost two thousand years after Plato, René Descartes also proposed a geometrically based alternative theory of atomism, without the problematic nothing–everything dichotomy of void, by the ancient definition however, directional information and magnitude were conceptually distinct. The explanation of a clepsydra or water clock was a topic in the Middle Ages. Although a simple wine skin sufficed to demonstrate a partial vacuum, in principle and he concluded that airs volume can expand to fill available space, and he suggested that the concept of perfect vacuum was incoherent. However, according to Nader El-Bizri, the physicist Ibn al-Haytham and the Mutazili theologians disagreed with Aristotle and Al-Farabi, using geometry, Ibn al-Haytham mathematically demonstrated that place is the imagined three-dimensional void between the inner surfaces of a containing body
34.
Electric spark
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Michael Faraday described this phenomenon as the beautiful flash of light attending the discharge of common electricity. The rapid transition from a non-conducting to a conductive state produces an emission of light. A spark is created when the electric field exceeds the dielectric breakdown strength of the intervening medium. For air, the strength is about 30 kV/cm at sea level. At the beginning stages, free electrons in the gap are accelerated by the electrical field, as they collide with air molecules, they create additional ions and newly freed electrons which are also accelerated. The exponentially-increasing electrons and ions rapidly cause regions of the air in the gap to become conductive in a process called dielectric breakdown. Once the gap breaks down, current flow is limited by the charge or by the impedance of the external power supply. If the power supply continues to supply current, the spark will evolve into a continuous discharge called an electric arc, an electric spark can also occur within insulating liquids or solids, but the breakdown mechanisms are significantly different than for sparks in gases. Lightning is an example of a spark in nature, while electric sparks, large or small, occur in or near many man-made objects. Around 600 BC, Greek philosopher Thales of Miletus observed that amber could be electrified when rubbed with a cloth and attract other objects, in 1671, Leibniz discovered that sparks were associated with electrical phenomena. In 1708, Samuel Wall performed experiments with amber rubbed with cloth to produce sparks, in 1752, Thomas-François Dalibard and Benjamin Franklin independently demonstrated that lightning and electricity were equivalent. In Franklins famous kite experiment, he successfully extracted sparks from a cloud during a thunderstorm, electric sparks are used in spark plugs in gasoline internal combustion engines to ignite fuel and air mixtures. The electric discharge in a spark plug occurs between a central electrode and a grounded terminal on the base of the plug. The voltage for the spark is provided by a coil or magneto that is connected to the spark plug with an insulated wire. Flame igniters use electric sparks to initiate combustion in some furnaces, auto reignition is a safety feature that is used in some flame igniters that senses the electrical conductivity of the flame and uses this information to determine whether a burner flame is lit. This information is used to stop an ignition device from sparking after the flame is lit or restart the flame if it goes out, a spark-gap transmitter uses an electric spark gap to generate radio frequency electromagnetic radiation that can be used as transmitters for wireless communication. Spark gap transmitters were used in the first three decades of radio from 1887–1916. They were later supplanted by vacuum tube systems and by 1940 were no longer used for communication, the wide use of spark-gap transmitters led to the nickname sparks for a ships radio officer
35.
Corona discharge
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A corona discharge is an electrical discharge brought on by the ionization of a fluid such as air surrounding a conductor that is electrically charged. Spontaneous corona discharges occur naturally in high-voltage systems unless care is taken to limit the field strength. It is often seen as a glow in the air adjacent to pointed metal conductors carrying high voltages. In many high voltage applications corona is a side effect. Corona discharge from high voltage power transmission lines constitutes an economically significant waste of power for utilities. In high voltage equipment like televisions, radio transmitters, X-ray machines, in air, coronas generate gases such as ozone and nitric oxide, and in turn nitrogen dioxide, and thus nitric acid if water vapor is present. These gases are corrosive and can degrade and embrittle nearby materials, corona discharges can often be suppressed by improved insulation, corona rings, and making high voltage electrodes in smooth rounded shapes. However, controlled corona discharges are used in a variety of such as air filtration, photocopiers. The ions generated eventually pass charge to nearby areas of lower potential, when the potential gradient is large enough at a point in the fluid, the fluid at that point ionizes and it becomes conductive. If a charged object has a point, the electric field strength around that point will be much higher than elsewhere. Air near the electrode can become ionized, while more distant do not. When the air near the point becomes conductive, it has the effect of increasing the apparent size of the conductor, since the new conductive region is less sharp, the ionization may not extend past this local region. Outside this region of ionization and conductivity, the particles slowly find their way to an oppositely charged object and are neutralized. Corona discharge usually forms at highly curved regions on electrodes, such as corners, projecting points, edges of metal surfaces. The high curvature causes a high potential gradient at these locations, so that the air breaks down, Coronas may be positive or negative. This is determined by the polarity of the voltage on the curved electrode. If the curved electrode is positive with respect to the electrode, it has a positive corona, if it is negative. The physics of positive and negative coronas are strikingly different, an important reason for considering coronas is the production of ozone around conductors undergoing corona processes in air
36.
Soda-lime glass
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Soda-lime glass, also called soda-lime-silica glass, is the most prevalent type of glass, used for windowpanes and glass containers for beverages, food, and some commodity items. Glass bakeware is often made of tempered soda-lime glass, soda-lime glass accounts for about 90% of manufactured glass. Soda-lime glass is relatively inexpensive, chemically stable, reasonably hard, because it can be resoftened and remelted numerous times, it is ideal for glass recycling. The temperature is limited by the quality of the furnace superstructure material. Relatively inexpensive minerals such as trona, sand, and feldspar are usually used instead of pure chemicals, green and brown bottles are obtained from raw materials containing iron oxide. The mix of raw materials is termed batch, soda-lime glass is divided technically into glass used for windows, called flat glass, and glass for containers, called container glass. The two types differ in the application, production method, and chemical composition, flat glass has a higher magnesium oxide and sodium oxide content than container glass, and a lower silica, calcium oxide, and aluminium oxide content. From the lower content of highly water-soluble ions in container glass comes its slightly higher chemical durability against water, the following table lists some physical properties of soda-lime glasses. Unless otherwise stated, the compositions and many experimentally determined properties are taken from one large study. Those values marked in italic font have been interpolated from similar glass compositions due to the lack of experimental data. Coefficient of restitution,0.97 ±0.01 Thermal conductivity,0. 7-1.3 W/m. K Hardness,6 Knoop hardness,585 kg/mm2 +20 Glass batch calculation
37.
Hygroscopy
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Hygroscopy is the phenomenon of attracting and holding water molecules from the surrounding environment, which is usually at normal or room temperature. This is achieved through either absorption or adsorption with the absorbing or adsorbing substance becoming physically changed somewhat. Zinc chloride and calcium chloride, as well as potassium hydroxide and sodium hydroxide, are so hygroscopic that they readily dissolve in the water they absorb, not only is sulfuric acid hygroscopic in concentrated form but its solutions are hygroscopic down to concentrations of 10 Vol-% or below. A hygroscopic material will tend to damp and cakey when exposed to moist air. Because of their affinity for moisture, hygroscopic materials might require storage in sealed containers. When added to foods or other materials for the purpose of maintaining moisture content. Materials and compounds exhibit different hygroscopic properties, and this difference can lead to detrimental effects, differences in hygroscopy can be observed in plastic-laminated paperback book covers—often, in a suddenly moist environment, the book cover will curl away from the rest of the book. The unlaminated side of the cover absorbs more moisture than the side and increases in area. This is similar to the function of a thermostats bi-metallic strip, inexpensive dial-type hygrometers make use of this principle using a coiled strip. Deliquescence, the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water, deliquescence occurs when the vapour pressure of the solution that is formed is less than the partial pressure of water vapour in the air. While some similar forces are at work here, it is different from capillary attraction, a process where glass or other solid substances attract water, the similar-sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is a device used for making observations deep under water. The amount of moisture held by hygroscopic materials is proportional to the relative humidity. Tables containing this information can be found in engineering handbooks and is also available from suppliers of various materials and chemicals. Hygroscopy also plays an important role in the engineering of plastic materials, some plastics are hygroscopic while others are not. The seeds of grasses have hygroscopic extensions that bend with changes in humidity. An example is Needle-and-Thread, Hesperostipa comata, each seed has an awn that twists several turns when the seed is released. Increased moisture causes it to untwist, and, upon drying, to twist again, thorny dragons collect moisture in the dry desert via nighttime condensation of dew that forms on their skin and is channeled to their mouths in hygroscopic grooves between the spines of their skin
38.
Pint
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The pint /ˈpaɪnt/ is a unit of volume or capacity in both the imperial and United States customary measurement systems. In both of those systems it is traditionally one-eighth of a gallon, Imperial or U. S. although measuring a different amount of liquid, the British pint is thus about 20% larger than the American pint. Almost all other countries have standardized on the metric system, the size of what may be called a pint varies depending on local custom. The imperial pint is used in the United Kingdom and Ireland, in the United States, two pints are used, a liquid pint and a less-common dry pint. Each of these pints is one-eighth of its respective gallon, but the gallons differ, the imperial pint consists of 20 imperial fluid ounces and the US liquid pint is 16 US fluid ounces, making the imperial fluid ounce about 4% smaller than the US fluid ounce. In the United Kingdom, the pint is still the primary unit for draught beer and cider. Historically, units called a pint were used much of Europe. Within continental Europe, the pint was replaced with the system during the 19th century. The imperial pint is equal to one-eighth of an imperial gallon, the United States liquid pint is equal to one-eighth of a United States liquid gallon. It is used commonly in the United States, the United States dry pint is equal to one-eighth of a United States dry gallon. It is used in the United States, but is not as common as the liquid pint, a now-obsolete unit of measurement in Scotland known as the Scottish pint or joug equals three imperial pints. It remained in use until the 19th century, surviving significantly longer than most of the old Scottish measurements, the French word pinte is etymologically related, but historically described a larger unit. The Royal pint was 48 French cubic inches and this is one of numerous false friends which exist between English and French. They are not the same although they have the same linguistic origin - the French Canadian pinte is actually equivalent to the English quart. If you want to order an English pint of beer in Canadian French, the Imperial system of measurement is no longer taught in Canadian schools, so servers may be unclear on how big a pint or pinte is regardless of language. In Flanders, the word pintje, meaning little pint, refers only to a 250 mL glass of lager, some West- and East-Flemish dialects use it as a word for beaker. The equivalent word in German, Pintchen, refers to a glass of a third of a litre in Cologne, one US fluid pint of water weighs about a pound, resulting in the popular saying, The pints a pound, the world around. A different saying for the pint is a pint of pure water weighs a pound
39.
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
40.
Dielectric absorption
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Dielectric absorption is the name given to the effect by which a capacitor, that has been charged for a long time, discharges only incompletely when briefly discharged. For some dielectrics, such as many films, the resulting voltage may be less than 1–2% of the original voltage. The voltage at the terminals generated by the dielectric absorption may possibly cause problems in the function of a circuit or can be a safety risk to personnel. In order to prevent shocks, most very large capacitors are shipped with shorting wires that need to be removed before they are used, charging a capacitor causes an electric field to be applied to the dielectric between the electrodes. This field exerts a torque on the molecular dipoles, causing the directions of the moments to align with the field direction. This change in the dipoles is called oriented polarization and also causes heat to be generated. The orientation of the dipoles does not follow the electric field synchronously and this delay corresponds to a hysteresis response of the polarization to the external field. When the capacitor is discharging, the strength of the field is decreasing. This is like an electrical remanence, the oriented dipoles will be discharged spontaneously over time and the voltage at the electrodes of the capacitor will decay exponentially. The complete discharge time of all dipoles can be days to weeks depending on the material and this reloaded voltage can be retained for months, even in electrolytic capacitors, caused by the high insulation resistance in common modern capacitor dielectrics. The discharge of a capacitor and the subsequent reloading can be repeated several times, an example of the reloading of a capacitor is shown by a measurement in this YouTube video and also illustrated by using the Java circuit simulator. Dielectric absorption is a property which has long known. Its value can be measured in accordance with the IEC/EN 60384-1 standard, the capacitor shall be charged at the DC voltage rating for 60 minutes. Then the capacitor shall be disconnected from the source and shall be discharged for 10 s. The voltage regained on the capacitor terminals within 15 minutes is the dielectric absorption voltage, the size of the dielectric absorption voltage is specified in relation to the applied voltage in percent and depends on the dielectric material used. It is specified by manufacturers in the data sheets. The voltage at the terminals generated by the dielectric absorption may possibly cause problems in the function of an electronic circuit, for most electronic circuits, particularly filtering applications, the small dielectric absorption voltage has no influence on the proper electrical function of the circuit. For aluminum electrolytic capacitors with non-solid electrolyte which are not built into a circuit, the voltage can be quite substantial, for example 50 V for 400 V electrolytic capacitors, and can cause damages to semiconductor devices, or cause sparks during installation in the circuit
Chisholm, Hugh, ed. (1911). "Leyden Jar". Encyclopædia Britannica (11th ed.). Cambridge University Press.
"Leyden Jar". Encyclopædia Britannica (11th ed.). 1911.
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