1.
Megatron
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Megatron is a character from the Transformers franchise, created by Hasbro in 1984, based on a toy design by Takara. The original Megatron was the Decepticon Leader, which could transform into three different types of guns, a Walther P38 handgun, a beam cannon. He is a sentient robotic lifeform from the planet Cybertron and the leader of the villainous Decepticons as well as the archenemy of the Autobot leader Optimus Prime, Megatron is usually depicted as having risen up from the lowly worker to become a champion in gladiatorial combat. As a gladiator, he took the legendary name Megatronus as his own, Prime would later use his teachings against him when he became corrupt. He has the ability to transform between his robot shape and various weapons or vehicles, but these alternate-modes, his origins and even personality and this origin is considered the most consistent between the various incarnations. Further differences are listed in the sections below. The original Megatronus, better known as the Fallen, was one of the original Thirteen Primes created by Primus, Megatronus betrayed his creator by siding with Primus dark twin, the malevolent planet-eater Unicron. In the final battle between Primus and Unicron, Megatronus fell victim to the fate as his master, sucked through a black hole into another dimension. However, while Unicron emerged in another universe, the Fallen was not so fortunate, another being addressed simply as Megatron is an apocalyptic figure said to bring about death and destruction through alteration of the time stream. Possible interpretations in the book of him are Alpha and Omega, the Fallen made his first appearance in the second volume of Transformers, The War Within. The character appears as the main antagonist in the live action film, Transformers, Revenge of the Fallen. Director Michael Bay described him as apocalyptic and he has the ability to teleport and generate a shockwave upon reappearance. He wields a spear as his weapon and has the ability of telekinesis, Megatronus is also mentioned as one of Thirteen in Transformers, Exodus and later appeared as the main antagonist in the first-season finale of Transformers, Robots in Disguise, voiced by Gil Gerard. Megatronuss history would be retconned in Transformers, The Covenant of Primus, Megatronus was one of the original thirteen Primes. Megatronus commissioned Solus Prime to create the Requiem Blaster, following the War of the Primes, he exiled himself from Cybertron after unintentionally murdering Solus Prime. Megatron is the founder of the Decepticon uprising and their most feared leader, bob Budiansky, the writer for the Marvel Comics series, stated that originally Hasbro took issue with the name, saying it sounded too frightening. Budiansky responded that as the villain, that was the point. Hasbro later agreed with his reasoning, and approved the name Megatron, the name itself probably comes from the Greek word megas, although in one of his interviews Budiansky claimed that it is in fact a portmanteau of electronic and megaton
2.
Alnico
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Alnico is an acronym referring to a family of iron alloys which in addition to iron are composed primarily of aluminium, nickel and cobalt, hence al-ni-co. They also include copper, and sometimes titanium, Alnico alloys are ferromagnetic, with a high coercivity and are used to make permanent magnets. Before the development of rare-earth magnets in the 1970s, they were the strongest type of permanent magnet, other trade names for alloys in this family are, Alni, Alcomax, Hycomax, Columax, and Ticonal. The composition of alnico alloys is typically 8–12% Al, 15–26% Ni, 5–24% Co, up to 6% Cu, up to 1% Ti, Alnico alloys can be magnetised to produce strong magnetic fields and have a high coercivity, thus making strong permanent magnets. Of the more commonly available magnets, only rare-earth magnets such as neodymium, Alnico magnets produce magnetic field strength at their poles as high as 1500 gausses, or about 3000 times the strength of Earths magnetic field. Some brands of alnico are isotropic and can be magnetized in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, with each having a direction of magnetization. Anisotropic alloys generally have greater capacity in a preferred orientation than isotropic types. Alnicos remanence may exceed 12,000 G, its coercivity can be up to 1000 oersteds and this means that alnico can produce a strong magnetic flux in closed magnetic circuits, but has relatively small resistance against demagnetization. The field strength at the poles of any permanent magnet depends very much on the shape and is well below the remanence strength of the material. Alnico alloys have some of the highest Curie temperatures of any material, around 800 °C. They are the only magnets that have useful magnetism even when heated red-hot and this property, as well as its brittleness and high melting point, is the result of the strong tendency toward order due to intermetallic bonding between aluminium and other constituents. They are also one of the most stable if they are handled properly. Alnico magnets are electrically conductive, unlike ceramic magnets, as of 2008, Alnico magnets cost about 44 USD/kg or 4.30 USD/BHmax. Alnico magnets are traditionally classified using numbers assigned by the Magnetic Materials Producers Association, for example and these classifications indicate chemical composition and magnetic properties. Alnico magnets are produced by casting or sintering processes, anisotropic alnico magnets are oriented by heating above a critical temperature and cooling in the presence of a magnetic field. After the heat treatment alnico becomes a material, named precipitation material—it consists of iron-. Without an external field there are local anisotropies of different orientations due to spontaneous magnetization, the precipitate structure is a barrier against magnetization changes, as it prefers few magnetization states requiring much energy to get the material into any intermediate state
3.
Rare-earth magnet
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Rare-earth magnets are strong permanent magnets made from alloys of rare earth elements. The magnetic field produced by rare-earth magnets can exceed 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types, neodymium magnets and samarium-cobalt magnets, magnetostrictive rare-earth magnets such as Terfenol-D also have applications—e. g. in loudspeakers. Rare earth magnets are brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping. The term rare earth can be misleading as these metals are not particularly rare or precious, however, they form compounds with the transition metals such as iron, nickel, and cobalt, and some of these have Curie temperatures well above room temperature. Rare earth magnets are made from these compounds, the greater strength of rare earth magnets is mostly due to two factors. First, their structures have very high magnetic anisotropy. This means a crystal of the material preferentially magnetizes along a specific crystal axis but is difficult to magnetize in other directions. The resistance of the lattice to turning its direction of magnetization gives these compounds a very high magnetic coercivity. This is a consequence of incomplete filling of the f-shell, which can contain up to 7 unpaired electrons, in a magnet it is the unpaired electrons, aligned so they spin in the same direction, which generate the magnetic field. This gives the materials high remanence, the maximum energy density BHmax is proportional to Js2 so these materials have the potential for storing large amounts of magnetic energy. The magnetic energy product BHmax of neodymium magnets is about 18 times greater than ordinary magnets by volume and this allows rare earth magnets to be smaller than other magnets which produce the same field strength. Rare earth magnets have higher remanence, much higher coercivity and energy product, the table below compares the magnetic performance of the two types of rare earth magnet, neodymium and samarium-cobalt, with other types of permanent magnets. Source, Samarium–cobalt magnets, the first family of rare earth magnets invented, are used than neodymium magnets because of their higher cost. However, samarium–cobalt has a higher Curie temperature, creating a niche for these magnets in applications where high strength is needed at high operating temperatures. They are highly resistant to oxidation, but sintered samarium-cobalt magnets are brittle and prone to chipping and cracking, neodymium magnets, invented in the 1980s, are the strongest and most affordable type of rare-earth magnet. They are made of an alloy of neodymium, iron, and boron, neodymium magnets are used in numerous applications requiring strong, compact permanent magnets, such as electric motors for cordless tools, hard disk drives, magnetic holddowns, and jewelry clasps. They have the highest magnetic field strength and have a higher coercivity, corrosion can cause unprotected magnets to spall off a surface layer, or to crumble into a powder
4.
Vacuum tube
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In electronics, a vacuum tube, an electron tube, or just a tube, or valve, is a device that controls electric current between electrodes in an evacuated container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament and this type is called a thermionic tube or thermionic valve. A phototube, however, achieves electron emission through the photoelectric effect, the simplest vacuum tube, the diode, contains only a heater, a heated electron-emitting cathode, and a plate. Current can only flow in one direction through the device between the two electrodes, as electrons emitted by the travel through the tube and are collected by the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grid or grids, Tubes with grids can be used for many purposes, including amplification, rectification, switching, oscillation, and display. In the 1940s the invention of devices made it possible to produce solid-state devices, which are smaller, more efficient, more reliable, more durable. Hence, from the mid-1950s solid-state devices such as transistors gradually replaced tubes, the cathode-ray tube remained the basis for televisions and video monitors until superseded in the 21st century. However, there are still a few applications for which tubes are preferred to semiconductors, for example, the used in microwave ovens. One classification of vacuum tubes is by the number of active electrodes, a device with two active elements is a diode, usually used for rectification. Devices with three elements are used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have additional functions made possible by the additional controllable electrodes. X-ray tubes are vacuum tubes. Phototubes and photomultipliers rely on electron flow through a vacuum, though in those cases electron emission from the cathode depends on energy from photons rather than thermionic emission, since these sorts of vacuum tubes have functions other than electronic amplification and rectification they are described in their own articles. A vacuum tube consists of two or more electrodes in a vacuum inside an airtight enclosure, most tubes have glass envelopes, though ceramic and metal envelopes have been used. The electrodes are attached to leads which pass through the envelope via an airtight seal, Tubes were a frequent cause of failure in electronic equipment, and consumers were expected to be able to replace tubes themselves. In addition to the terminals, some tubes had an electrode terminating at a top cap. The principal reason for doing this was to avoid leakage resistance through the tube base, the bases were commonly made with phenolic insulation which performs poorly as an insulator in humid conditions. There was even a design that had two top cap connections
5.
Microwave
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Microwaves are a form of electromagnetic radiation with wavelengths ranging from one meter to one millimeter, with frequencies between 300 MHz and 300 GHz. Different sources define different frequency ranges as microwaves, the broad definition includes both UHF and EHF bands. A more common definition in radio engineering is the range between 1 and 100 GHz, in all cases, microwaves include the entire SHF band at minimum. Frequencies in the range are often referred to by their IEEE radar band designations, S, C, X, Ku, K, or Ka band. The prefix micro- in microwave is not meant to suggest a wavelength in the micrometer range and it indicates that microwaves are small, compared to waves used in typical radio broadcasting, in that they have shorter wavelengths. The boundaries between far infrared, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. At the high end of the band they are absorbed by gases in the atmosphere, microwaves are extremely widely used in modern technology. Although at the low end of the band they can pass through building walls enough for useful reception, therefore on the surface of the Earth microwave communication links are limited by the visual horizon to about 30 -40 miles. Microwaves are absorbed by moisture in the atmosphere, and the attenuation increases with frequency, beginning at about 40 GHz, atmospheric gases also begin to absorb microwaves, so above this frequency microwave transmission is limited to a few kilometers. A spectral band structure causes absorption peaks at specific frequencies, in a microwave beam directed at an angle into the sky, a small amount of the power will be randomly scattered as the beam passes through the troposphere. A sensitive receiver beyond the horizon with a high gain antenna focused on that area of the troposphere can pick up the signal. This technique has been used at frequencies between 0.45 and 5 GHz in tropospheric scatter communication systems to communicate beyond the horizon and their short wavelength allows narrow beams of microwaves to be produced by conveniently small high gain antennas from a half meter to 5 meters in diameter. Therefore beams of microwaves are used for point-to-point communication links, an advantage of narrow beams is that they allow frequency reuse by nearby transmitters. Parabolic antennas are the most widely used directive antennas at microwave frequencies, flat microstrip antennas are being increasingly used in consumer devices. Where omnidirectional antennas are required, for example in wireless devices and Wifi routers for wireless LANs, small monopoles, dipole, or patch antennas are used. Due to the high cost and maintenance requirements of waveguide runs, the term microwave also has a more technical meaning in electromagnetics and circuit theory. As a consequence, practical microwave circuits tend to away from the discrete resistors, capacitors. Open-wire and coaxial transmission lines used at lower frequencies are replaced by waveguides and stripline, high-power microwave sources use specialized vacuum tubes to generate microwaves
6.
Electron
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The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, the electron has a mass that is approximately 1/1836 that of the proton. Quantum mechanical properties of the include a intrinsic angular momentum of a half-integer value, expressed in units of the reduced Planck constant. As it is a fermion, no two electrons can occupy the same state, in accordance with the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of particles and waves, they can collide with other particles and can be diffracted like light. Since an electron has charge, it has an electric field. Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law, electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields, special telescopes can detect electron plasma in outer space. Electrons are involved in applications such as electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors. Interactions involving electrons with other particles are of interest in fields such as chemistry. The Coulomb force interaction between the positive protons within atomic nuclei and the negative electrons without, allows the composition of the two known as atoms, ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the cause of chemical bonding. In 1838, British natural philosopher Richard Laming first hypothesized the concept of a quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge electron in 1891, electrons can also participate in nuclear reactions, such as nucleosynthesis in stars, where they are known as beta particles. Electrons can be created through beta decay of isotopes and in high-energy collisions. The antiparticle of the electron is called the positron, it is identical to the electron except that it carries electrical, when an electron collides with a positron, both particles can be totally annihilated, producing gamma ray photons. The ancient Greeks noticed that amber attracted small objects when rubbed with fur, along with lightning, this phenomenon is one of humanitys earliest recorded experiences with electricity. In his 1600 treatise De Magnete, the English scientist William Gilbert coined the New Latin term electricus, both electric and electricity are derived from the Latin ēlectrum, which came from the Greek word for amber, ἤλεκτρον
7.
Magnetic field
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A magnetic field is the magnetic effect of electric currents and magnetic materials. The magnetic field at any point is specified by both a direction and a magnitude, as such it is represented by a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H, where H is measured in units of amperes per meter in the SI, B is measured in teslas and newtons per meter per ampere in the SI. B is most commonly defined in terms of the Lorentz force it exerts on moving electric charges, Magnetic fields can be produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin. In quantum physics, the field is quantized and electromagnetic interactions result from the exchange of photons. Magnetic fields are used throughout modern technology, particularly in electrical engineering. The Earth produces its own field, which is important in navigation. Rotating magnetic fields are used in electric motors and generators. Magnetic forces give information about the carriers in a material through the Hall effect. The interaction of magnetic fields in electric devices such as transformers is studied in the discipline of magnetic circuits, noting that the resulting field lines crossed at two points he named those points poles in analogy to Earths poles. He also clearly articulated the principle that magnets always have both a north and south pole, no matter how finely one slices them, almost three centuries later, William Gilbert of Colchester replicated Petrus Peregrinus work and was the first to state explicitly that Earth is a magnet. Published in 1600, Gilberts work, De Magnete, helped to establish magnetism as a science, in 1750, John Michell stated that magnetic poles attract and repel in accordance with an inverse square law. Charles-Augustin de Coulomb experimentally verified this in 1785 and stated explicitly that the north and south poles cannot be separated, building on this force between poles, Siméon Denis Poisson created the first successful model of the magnetic field, which he presented in 1824. In this model, a magnetic H-field is produced by magnetic poles, three discoveries challenged this foundation of magnetism, though. First, in 1819, Hans Christian Ørsted discovered that an electric current generates a magnetic field encircling it, then in 1820, André-Marie Ampère showed that parallel wires having currents in the same direction attract one another. Finally, Jean-Baptiste Biot and Félix Savart discovered the Biot–Savart law in 1820, extending these experiments, Ampère published his own successful model of magnetism in 1825. This has the benefit of explaining why magnetic charge can not be isolated. Also in this work, Ampère introduced the term electrodynamics to describe the relationship between electricity and magnetism, in 1831, Michael Faraday discovered electromagnetic induction when he found that a changing magnetic field generates an encircling electric field
8.
Cavity resonator
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The oscillations in a resonator can be either electromagnetic or mechanical. Resonators are used to generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones, another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency. A cavity resonator is one in which waves exist in a space inside the device. Acoustic cavity resonators, in sound is produced by air vibrating in a cavity with one opening, are known as Helmholtz resonators. A physical system can have as many resonant frequencies as it has degrees of freedom, systems with one degree of freedom, such as a mass on a spring, pendulums, balance wheels, and LC tuned circuits have one resonant frequency. Systems with two degrees of freedom, such as coupled pendulums and resonant transformers can have two resonant frequencies, a crystal lattice composed of N atoms bound together can have N resonant frequencies. As the number of coupled harmonic oscillators grows, the time it takes to transfer energy from one to the next becomes significant, the vibrations in them begin to travel through the coupled harmonic oscillators in waves, from one oscillator to the next. The term resonator is most often used for an object in which vibrations travel as waves, at an approximately constant velocity, bouncing back. The material of the resonator, through which the waves flow, therefore, they can have millions of resonant frequencies, although only a few may be used in practical resonators. The oppositely moving waves interfere with other, and at its resonant frequencies reinforce each other to create a pattern of standing waves in the resonator. If the distance between the sides is d, the length of a trip is 2 d. To cause resonance, the phase of a sinusoidal wave after a round trip must be equal to the initial phase so the waves self-reinforce. The above analysis assumes the medium inside the resonator is homogeneous, so the waves travel at a constant speed, and they are then called overtones instead of harmonics. There may be several such series of resonant frequencies in a single resonator, an electrical circuit composed of discrete components can act as a resonator when both an inductor and capacitor are included. Oscillations are limited by the inclusion of resistance, either via a specific resistor component, such resonant circuits are also called RLC circuits after the circuit symbols for the components. A distributed-parameter resonator has capacitance, inductance, and resistance that cannot be isolated into separate lumped capacitors, inductors, an example of this, much used in filtering, is the helical resonator. A single layer coil that is used as a secondary or tertiary winding in a Tesla coil or magnifying transmitter is also a distributed resonator
9.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope
10.
Resonant frequency
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In physics, resonance is a phenomenon in which a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency. Frequencies at which the amplitude is a relative maximum are known as the systems resonant frequencies or resonance frequencies. At resonant frequencies, small periodic driving forces have the ability to produce large amplitude oscillations, Resonance occurs when a system is able to store and easily transfer energy between two or more different storage modes. However, there are some losses from cycle to cycle, called damping, when damping is small, the resonant frequency is approximately equal to the natural frequency of the system, which is a frequency of unforced vibrations. Some systems have multiple, distinct, resonant frequencies, resonant systems can be used to generate vibrations of a specific frequency, or pick out specific frequencies from a complex vibration containing many frequencies. Resonance occurs widely in nature, and is exploited in many manmade devices and it is the mechanism by which virtually all sine waves and vibrations are generated. Many sounds we hear, such as when hard objects of metal, glass, light and other short wavelength electromagnetic radiation is produced by resonance on an atomic scale, such as electrons in atoms. A familiar example is a swing, which acts as a pendulum. Pushing a person in a swing in time with the interval of the swing makes the swing go higher and higher. This is because the energy the swing absorbs is maximized when the match the swings natural oscillations. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings, trains, avoiding resonance disasters is a major concern in every building, tower, and bridge construction project. As a countermeasure, shock mounts can be installed to absorb resonant frequencies, the Taipei 101 building relies on a 660-tonne pendulum —a tuned mass damper—to cancel resonance. Furthermore, the structure is designed to resonate at a frequency that does not typically occur, buildings in seismic zones are often constructed to take into account the oscillating frequencies of expected ground motion. Clocks keep time by mechanical resonance in a wheel, pendulum. The cadence of runners has been hypothesized to be energetically favorable due to resonance between the energy stored in the lower limb and the mass of the runner. Acoustic resonance is a branch of mechanical resonance that is concerned with the mechanical vibrations across the range of human hearing. Like mechanical resonance, acoustic resonance can result in failure of the object at resonance. The classic example of this is breaking a glass with sound at the precise resonant frequency of the glass
11.
Klystron
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In a klystron, an electron beam interacts with radio waves as it passes through resonant cavities, metal boxes along the length of a tube. The electron beam first passes through a cavity to which the signal is applied. The energy of the electron beam amplifies the signal, and the signal is taken from a cavity at the other end of the tube. The output signal can be coupled back into the cavity to make an electronic oscillator to generate radio waves. The gain of klystrons can be high,60 dB or more, with power up to tens of megawatts. A reflex klystron is a type in which the electron beam was reflected back along its path by a high potential electrode. The name klystron comes from the stem form κλυσ- of a Greek verb referring to the action of waves breaking against a shore, the name klystron was suggested by Hermann Fränkel, a professor in the classics department at Stanford University when the klystron was under development. The klystron was the first significantly powerful source of waves in the microwave range. Before its invention the only sources were the Barkhausen-Kurz tube and split anode magnetron, the klystron was invented by the brothers Russell and Sigurd Varian at Stanford University. Their prototype was completed and demonstrated successfully on August 30,1937, upon publication in 1939, news of the klystron immediately influenced the work of US and UK researchers working on radar equipment. The Varians went on to found Varian Associates to commercialize the technology and their work built on the description of velocity modulation by A. Arsenjewa-Heil and Oskar Heil in 1935, though the Varians were probably unaware of the Heils work. Hansen was instrumental in the development of the klystron and was cited by the Varian brothers in their 1939 paper and his resonator analysis, which dealt with the problem of accelerating electrons toward a target, could be used just as well to decelerate electrons. During the second World War, Hansen lectured at the MIT Radiation labs two days a week, commuting to Boston from Sperry Gyroscope Company on Long Island and his resonator was called a rhumbatron by the Varian brothers. Hansen died of disease in 1949 as a result of exposure to beryllium oxide. Klystron tube technologies for very high-power applications, such as synchrotrons, right after the war, AT&T used 4 watt klystrons in its brand new network of microwave relay links that covered the US continent. The network provided long distance telephone service and also carried television signals for the major TV networks, klystrons amplify RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. A beam of electrons is produced by a cathode. This beam is passed through an input cavity resonator
12.
Traveling-wave tube
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A traveling-wave tube or traveling-wave tube amplifier is a specialized vacuum tube that is used in electronics to amplify radio frequency signals in the microwave range. The TWT belongs to a category of linear beam tubes, such as the klystron, although there are various types of TWT, two major categories are, Helix TWT In which the radio waves interact with the electron beam while traveling down a wire helix which surrounds the beam. These have wide bandwidth, but output power is limited to a few hundred watts, coupled cavity TWT In which the radio wave interacts with the beam in a series of cavity resonators through which the beam passes. These function as narrowband power amplifiers, a major advantage of the TWT over some other microwave tubes is its ability to amplify a wide range of frequencies, a wide bandwidth. The bandwidth of the helix TWT can be as high as two octaves, while the cavity versions have bandwidths of 10–20%, operating frequencies range from 300 MHz to 50 GHz. The power gain of the tube is on the order of 40 to 70 decibels, TWTs account for over 50% of the sales volume of all microwave vacuum tubes. They are widely used as the power amplifiers and oscillators in radar systems, communication satellite and spacecraft transmitters, the TWT is an elongated vacuum tube with an electron gun at one end. A voltage applied across the cathode and anode accelerates the electrons towards the far end of the tube, at the other end of the tube the electrons strike the collector, which returns them to the circuit. Wrapped around the inside of the tube, just outside the path, is a helix of wire. The RF signal to be amplified is fed into the helix at a point near the end of the tube. The signal is fed into the helix via a waveguide or electromagnetic coil placed at one end, forming a one-way signal path. By controlling the voltage, the speed of the electrons flowing down the tube is set to be similar to the speed of the RF signal running down the helix. The signal in the causes an magnetic field to be induced in the center of the helix. Depending on the phase of the signal, the electrons will either be sped up or slowed down as they pass the windings and this causes the electron beam to bunch up, known technically as velocity modulation. The resulting pattern of electron density in the beam is an analog of the original RF signal, because the beam is passing the helix as it travels, and that signal varies, it causes induction in the helix, amplifying the original signal. By the time it reaches the end of the tube. A second directional coupler, positioned near the collector, receives an amplified version of the signal from the far end of the RF circuit. Attenuators placed along the RF circuit prevent the wave from traveling back to the cathode
13.
Amplifier
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An amplifier, electronic amplifier or amp is an electronic device that can increase the power of a signal. An amplifier functions by taking power from a supply and controlling the output to match the input signal shape. In this sense, an amplifier modulates the output of the power supply based upon the properties of the input signal, an amplifier is effectively the opposite of an attenuator, while an amplifier provides gain, an attenuator provides loss. An amplifier can either be a piece of equipment or an electrical circuit contained within another device. Amplification is fundamental to modern electronics, and amplifiers are used in almost all electronic equipment. Amplifiers can be categorized in different ways, another is which quantity, voltage or current is being amplified, amplifiers can be divided into voltage amplifiers, current amplifiers, transconductance amplifiers, and transresistance amplifiers. A further distinction is whether the output is a linear or nonlinear representation of the input, amplifiers can also be categorized by their physical placement in the signal chain. The first practical device that could amplify was the triode vacuum tube, invented in 1906 by Lee De Forest. Vacuum tubes were used in almost all amplifiers until the 1960s–1970s when the transistor, invented in 1947, today most amplifiers use transistors, but vacuum tubes continue to be used in some applications. Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After the turn of the century it was found that negative resistance mercury lamps could amplify, the first practical electronic device that could amplify was the Audion vacuum tube, invented in 1906 by Lee De Forest, which led to the first amplifiers around 1912. The terms amplifier and amplification were first used for this new capability around 1915 when triodes became widespread, the amplifying vacuum tube revolutionized electrical technology, creating the new field of electronics, the technology of active electrical devices. It made possible long distance lines, public address systems, radio broadcasting, talking motion pictures, practical audio recording, radar, television. For 50 years virtually all electronic devices used vacuum tubes. Early tube amplifiers often had positive feedback, which could increase gain but also make the amplifier unstable, much of the mathematical theory of amplifiers was developed at Bell Telephone Laboratories during the 1920s to 1940s. Other advances in the theory of amplification were made by Harry Nyquist, the vacuum tube was the only amplifying device for 40 years, and dominated electronics until 1947, when the first transistor, the BJT, was invented. Today most amplifiers use transistors, but vacuum tubes are used in some high power applications such as radio transmitters. All amplifiers have gain, a factor that relates the magnitude of some property of the output signal to a property of the input signal
14.
Electronic oscillator
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An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave. Oscillators convert direct current from a supply to an alternating current signal. They are widely used in electronic devices. Oscillators are often characterized by the frequency of their output signal and this term is typically used in the field of audio synthesizers, to distinguish it from an audio frequency oscillator. An audio oscillator produces frequencies in the range, about 16 Hz to 20 kHz. An RF oscillator produces signals in the frequency range of about 100 kHz to 100 GHz. Oscillators designed to produce a high-power AC output from a DC supply are usually called inverters, there are two main types of electronic oscillator, the linear or harmonic oscillator and the nonlinear or relaxation oscillator. The harmonic, or linear, oscillator produces a sinusoidal output, when the power supply to the amplifier is first switched on, electronic noise in the circuit provides a non-zero signal to get oscillations started. The noise travels around the loop and is amplified and filtered until very quickly it converges on a wave at a single frequency. RC oscillators are used to generate lower frequencies, for example in the audio range. Common types of RC oscillator circuits are the phase shift oscillator, in an LC oscillator circuit, the filter is a tuned circuit consisting of an inductor and capacitor connected together. Charge flows back and forth between the plates through the inductor, so the tuned circuit can store electrical energy oscillating at its resonant frequency. There are small losses in the circuit, but the amplifier compensates for those losses and supplies the power for the output signal. Typical LC oscillator circuits are the Hartley, Colpitts and Clapp circuits, in a crystal oscillator circuit the filter is a piezoelectric crystal. The crystal mechanically vibrates as a resonator, and its frequency of vibration determines the oscillation frequency, crystals have very high Q-factor and also better temperature stability than tuned circuits, so crystal oscillators have much better frequency stability than LC or RC oscillators. Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, crystal oscillators often use the same circuits as LC oscillators, with the crystal replacing the tuned circuit, the Pierce oscillator circuit is also commonly used. Quartz crystals are generally limited to frequencies of 30 MHz or below, other types of resonator, dielectric resonators and surface acoustic wave devices, are used to control higher frequency oscillators, up into the microwave range. For example, SAW oscillators are used to generate the signal in cell phones
15.
Albert W. Hull
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Albert Wallace Hull is an American physicist and electrical engineer who made contributions to the development of vacuum tubes, and invented the magnetron. He was a member of the National Academy of Sciences and he was born on 19 April 1880 in Southington, Connecticut. He majored in Greek and after taking one course in physics. He taught languages at The Albany Academy before returning to Yale and he then undertook research on photoelectricity whilst teaching physics for five years at the Worcester Polytechnic Institute. In 1914 Hull joined the General Electric Research Laboratory in Schenectady, New York, Hull was promoted to assistant director of the GERL in 1928. Hull was promoted to assistant director of the GERL in 1928 and he served as president of the American Physical Society in 1942. He retired from General Electric Research Laboratory in 1949 and he did consulting work and served on an advisory committee of the Army Ballistics Research Laboratories after retirement from General Electric. He died on 22 January 1966 at the age of 85 in Schenectady and he invented the dynatron vacuum tube which had three electrodes, a thermionic cathode, a perforated anode, and a supplementary anode or plate. In normal operation the supplementary anode was maintained at a positive voltage than the perforated anode. When a control grid was added between the cathode and the anode, the device was called a pliodynatron. By 1920 his research led to his invention of the magnetron and this took the form of a central cathode and a coaxial cylindrical anode split into two halves, with an axial magnetic field produced by an external coil. The Hull magnetron was tested as an amplifier in radio receivers and it was reported in 1925 that a magnetron made at GERL could generate a power of 15 kW at a frequency of 20 kHz. At the time Hull anticipated that the magnetron would find use as a power converter than in communication applications. Hulls split-anode magnetron didnt prove to be capable of frequency or high power output and was little used. During the 1920s, Hull also was a contributor to the development of gas-filled electron tubes at the GERL. He discovered how to protect thermionic cathodes from rapid disintegration under ion bombardment and this discovery enabled the successful development of hot-cathode thyratrons and phanotrons. In the 1918 issue of the Proceedings of the IRE he published a paper on the vacuum tube which he had invented. During his career in electronics he was the author or coauthor of 72 technical publications and was awarded 94 patents,1924 Howard N. Potts Medal of the Franklin Institute
16.
General Electric Research Laboratory
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General Electric Research Laboratory, the first industrial research facility in the United States, was established in 1900. It is located in Schenectady, New York, Schenectady is nicknamed The City that Lights and Hauls the World. This lab was home to the early breakthroughs of General Electric and created a research. It developed into GE Global Research that now covers an array of research, ranging from healthcare to transportation systems. It was designated a National Historic Landmark in 1975, founded in 1900 by Thomas Edison, Willis R. Whitney, and Charles Steinmetz, this lab defined industrial research for years to come. Furthermore, Edwin W. Rice, founding president, said they wanted to “establish a laboratory to be devoted exclusively to original research. It is hoped by this means that many profitable fields may be discovered. ”Whitney, German universities allowed professors to research and experiment with their own interests to seek further knowledge without having commercial or economic interests in mind. Other German scientists also researched exclusively with business in mind, but, these two views contributed to a successful relationship between science and industry. It was this success that influenced Whitney in his vision for the GE Research Lab, the laboratory began at a time when the American electrification process was in its infant stage. General Electric became the leader of this move toward electrifying the United States and developing new technologies for other science. Willis Whitney and his assistant, Thomas Dempster, were the key researchers in developing the technology that allowed the laboratory to continue to grow. The lab grew from 8 people to 102 people by 1906, Whitney believed in exploratory scientific research, with the goal of creating new commercial products. These two goals appealed to General Electric, for researchers, the lab provided time and money for experimentation, research, and personal interests without putting a high demand on developing theories or teaching. Nearly 30 years after its founding, the laboratory had expanded the staff to more than 400 chemists, physicists and it took several years for the lab to follow through with the vision to create all original innovations, instead of improving on the inventions already in place. GE’s earliest project was perfecting the incandescent light bulb, in 1908, engineer and new head researcher William Coolidge invented the ductile tungsten light bulb filament, providing a more durable and long-lasting light filament than the existing technology. “The invention secured GEs technological leadership in the market and epitomized the role of the GE research lab — bringing innovation to the marketplace, but, that work was still an improvement on existing technology and nothing entirely new. In the coming years, GE scientists earned two Nobel Prizes in chemistry and physics, in 1932, Irving Langmuir won the Nobel Prize in chemistry for his work on surface chemical reactions which helped him develop the gas-filled light bulb in 1916. After patenting many inventions, Langmuir developed his new light bulb which reinvented lights altogether, by 1928, due to Langmuirs innovation, GE held 96% of incandescent light sales in America
17.
History of radar
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The history of radar starts with experiments by Heinrich Hertz in the late 19th century that showed that radio waves were reflected by metallic objects. This possibility was suggested in James Clerk Maxwells seminal work on electromagnetism, numerous similar systems, which provided directional information to objects over short ranges, were developed over the next two decades. The development of systems able to produce pulses of radio energy was the key advance that allowed modern radar systems to come into existence. By timing the pulses on an oscilloscope, the range could be determined, the two, combined, produced a fix, locating the target relative to the antenna. During the war, Hungary was added to this list, the term RADAR was coined in 1939 by the United States Signal Corps as it worked on these systems for the Navy. Progress during the war was rapid and of importance, probably one of the decisive factors for the victory of the Allies. A key development was the magnetron in the UK, which allowed the creation of small systems with sub-meter resolution. By the end of hostilities, Britain, Germany, the United States, the USSR, after the war, radar use was widened to numerous fields including, civil aviation, marine navigation, radar guns for police, meteorology and even medicine. Increases in signal processing capability due to the introduction of solid state computers has also had a impact on radar use. The place of radar in the story of science and technology is argued differently by different authors. On the one hand, radar contributed very little to theory, therefore, radar did not advance science, but was simply a matter of technology and engineering. But others point out the practical consequences of the development of radar. Far more than the bomb, radar contributed to the Allied victory in World War II. Robert Buderi states that it was also the precursor of modern technology. From a review of his book, Radar has been the root of a wide range of achievements since the war, producing a veritable family tree of modern technologies. In later years radar was used in instruments, such as weather radar and radar astronomy. In Hertzs 1887 experiment he found that these waves would transmit through different types of materials and also would reflect off surfaces in his lab as well as conductors. The nature of these waves being similar to light in their ability to be reflected, refracted
18.
World War II
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World War II, also known as the Second World War, was a global war that lasted from 1939 to 1945, although related conflicts began earlier. It involved the vast majority of the worlds countries—including all of the great powers—eventually forming two opposing alliances, the Allies and the Axis. It was the most widespread war in history, and directly involved more than 100 million people from over 30 countries. Marked by mass deaths of civilians, including the Holocaust and the bombing of industrial and population centres. These made World War II the deadliest conflict in human history, from late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, and formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Poland, Finland, Romania and the Baltic states. In December 1941, Japan attacked the United States and European colonies in the Pacific Ocean, and quickly conquered much of the Western Pacific. The Axis advance halted in 1942 when Japan lost the critical Battle of Midway, near Hawaii, in 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained all of its territorial losses and invaded Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in South Central China and Burma, while the Allies crippled the Japanese Navy, thus ended the war in Asia, cementing the total victory of the Allies. World War II altered the political alignment and social structure of the world, the United Nations was established to foster international co-operation and prevent future conflicts. The victorious great powers—the United States, the Soviet Union, China, the United Kingdom, the Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers waned, while the decolonisation of Asia, most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to end pre-war enmities, the start of the war in Europe is generally held to be 1 September 1939, beginning with the German invasion of Poland, Britain and France declared war on Germany two days later. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or even the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935. The British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the forces of Mongolia and the Soviet Union from May to September 1939, the exact date of the wars end is also not universally agreed upon. It was generally accepted at the time that the war ended with the armistice of 14 August 1945, rather than the formal surrender of Japan
19.
Bell Labs
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Nokia Bell Labs is an American research and scientific development company, owned by Finnish company Nokia. Its headquarters are located in Murray Hill, New Jersey, in addition to laboratories around the rest of the United States. The historic laboratory originated in the late 19th century as the Volta Laboratory, Bell Labs was also at one time a division of the American Telephone & Telegraph Company, half-owned through its Western Electric manufacturing subsidiary. Eight Nobel Prizes have been awarded for work completed at Bell Laboratories, in 1880, the French government awarded Alexander Graham Bell the Volta Prize of 50,000 francs, approximately US$10,000 at that time for the invention of the telephone. Bell used the award to fund the Volta Laboratory in Washington, D. C. in collaboration with Sumner Tainter, the laboratory is also variously known as the Volta Bureau, the Bell Carriage House, the Bell Laboratory and the Volta Laboratory. The laboratory focused on the analysis, recording, and transmission of sound, Bell used his considerable profits from the laboratory for further research and education to permit the diffusion of knowledge relating to the deaf. This resulted in the founding of the Volta Bureau c,1887, located at Bells fathers house at 1527 35th Street in Washington, D. C. where its carriage house became their headquarters in 1889. In 1893, Bell constructed a new building, close by at 1537 35th St. specifically to house the lab, the building was declared a National Historic Landmark in 1972. In 1884, the American Bell Telephone Company created the Mechanical Department from the Electrical, the first president of research was Frank B. Jewett, who stayed there until 1940, ownership of Bell Laboratories was evenly split between AT&T and the Western Electric Company. Its principal work was to plan, design, and support the equipment that Western Electric built for Bell System operating companies and this included everything from telephones, telephone exchange switches, and transmission equipment. Bell Labs also carried out consulting work for the Bell Telephone Company, a few workers were assigned to basic research, and this attracted much attention, especially since they produced several Nobel Prize winners. Until the 1940s, the principal locations were in and around the Bell Labs Building in New York City. Of these, Murray Hill and Crawford Hill remain in existence, the largest grouping of people in the company was in Illinois, at Naperville-Lisle, in the Chicago area, which had the largest concentration of employees prior to 2001. Since 2001, many of the locations have been scaled down or closed. The Holmdel site, a 1.9 million square foot structure set on 473 acres, was closed in 2007, the mirrored-glass building was designed by Eero Saarinen. In August 2013, Somerset Development bought the building, intending to redevelop it into a commercial and residential project. The prospects of success are clouded by the difficulty of readapting Saarinens design and by the current glut of aging, eight Nobel Prizes have been awarded for work completed at Bell Laboratories
20.
Wavelength
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In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the waves shape repeats, and thus the inverse of the spatial frequency. Wavelength is commonly designated by the Greek letter lambda, the concept can also be applied to periodic waves of non-sinusoidal shape. The term wavelength is also applied to modulated waves. Wavelength depends on the medium that a wave travels through, examples of wave-like phenomena are sound waves, light, water waves and periodic electrical signals in a conductor. A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric, water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary, wavelength is a measure of the distance between repetitions of a shape feature such as peaks, valleys, or zero-crossings, not a measure of how far any given particle moves. For example, in waves over deep water a particle near the waters surface moves in a circle of the same diameter as the wave height. The range of wavelengths or frequencies for wave phenomena is called a spectrum, the name originated with the visible light spectrum but now can be applied to the entire electromagnetic spectrum as well as to a sound spectrum or vibration spectrum. In linear media, any pattern can be described in terms of the independent propagation of sinusoidal components. The wavelength λ of a sinusoidal waveform traveling at constant speed v is given by λ = v f, in a dispersive medium, the phase speed itself depends upon the frequency of the wave, making the relationship between wavelength and frequency nonlinear. In the case of electromagnetic radiation—such as light—in free space, the speed is the speed of light. Thus the wavelength of a 100 MHz electromagnetic wave is about, the wavelength of visible light ranges from deep red, roughly 700 nm, to violet, roughly 400 nm. For sound waves in air, the speed of sound is 343 m/s, the wavelengths of sound frequencies audible to the human ear are thus between approximately 17 m and 17 mm, respectively. Note that the wavelengths in audible sound are much longer than those in visible light, a standing wave is an undulatory motion that stays in one place. A sinusoidal standing wave includes stationary points of no motion, called nodes, the upper figure shows three standing waves in a box. The walls of the box are considered to require the wave to have nodes at the walls of the box determining which wavelengths are allowed, the stationary wave can be viewed as the sum of two traveling sinusoidal waves of oppositely directed velocities. Consequently, wavelength, period, and wave velocity are related just as for a traveling wave, for example, the speed of light can be determined from observation of standing waves in a metal box containing an ideal vacuum. In that case, the k, the magnitude of k, is still in the same relationship with wavelength as shown above
21.
John Randall (physicist)
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It is also the key component of microwave ovens. Randall also led the Kings College, London team which worked on the structure of DNA and his other staff included Rosalind Franklin, Raymond Gosling, Alex Stokes and Herbert Wilson, all involved in research on DNA. He married Doris, daughter of Josiah John Duckworth, a colliery surveyor and they had one son, Christopher, born in 1935. He also took an active interest in the mechanisms of such luminescence, when the war began in 1939, Oliphant was approached by the Admiralty about the possibility of building a radio source that operated at microwave frequencies. Such a system would allow a radar using it to see small objects like the periscopes of submerged U-boats, Oliphant began research using the klystron, a device introduced by Russell and Sigurd Varian between 1937 and 1939, and the only system known to efficiently generate microwaves. Klystrons of the era were very low-power devices, and Oliphants efforts were directed to greatly increasing their output. If this were successful, it created a problem, the klystron was an amplifier only. Oliphant put Randall and Harry Boot on this issue of producing a microwave oscillator, asking them to explore miniature Barkhausen–Kurz tubes for this role and their work quickly demonstrated that these offered no improvement in the microwave range. Randall and Boot, given no other projects to work on, in contrast, the magnetron used a conventional hot filament cathode, a system that was widely used in radio systems producing hundreds of kilowatts. This seemed to offer a more likely path to higher power. The problem with existing magnetrons was not power, but efficiency, in the klystron, a beam of electrons was passed through a metal disk known as a resonator. The mechanical layout of the copper resonator caused it to influence the electrons, speeding them up and slowing them down and this was reasonably efficient, and power was limited by the guns. There was no limit to the number of electrons this could accelerate. The two then considered what would happen if the two plates of the magnetron were replaced by resonators, essentially combining the existing magnetron and klystron concepts. More importantly, they was no limit to the number or size of these loops. One could greatly improve the power of the system by extending the loops into cylinders, efficiency could be improved by increasing the number of resonators, as each electron could thus interact with more resonators during its orbits. The only practical limits were based on the frequency and desired physical size of the tube. A test of their new cavity magnetron design in February 1940 produced 400 watts, the design was then demonstrated to engineers from GEC, who were asked to try to improve it
22.
Harry Boot
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He was born in Birmingham and attended King Edwards School, Birmingham and the University of Birmingham. While working on his PhD the war broke out and his professor Mark Oliphant had seen the klystron at Stanford University but it produced insufficient power to be useful as a radar transmitter. He assigned John Randall and Boot to the problem, by late February 1940, they had invented the much more powerful cavity magnetron which was fitted in an experimental radar by May 1940. James Sayers later refined the magnetron still further by strapping alternate cavities, as with many British inventions of this period, the magnetron was provided to the US for free when they entered World War II. Initially Boot and Randall were awarded £50 each for the magnetron for improving the safety of life at sea but later Boot, Randall and Sayers received a £36,000 prize in 1949 for their work. After a brief time at British Thomson-Houston, Rugby, in the years of the war. After some work on physics, Boot returned to magnetrons. He enjoyed sailing, owning two boats at Salcombe in Devon and he frequently went down there to the family holiday home with his wife Penelope, and his two sons, Christopher and Nicholas. He retired in 1977 and died in Cambridge on 8 February 1983
23.
University of Birmingham
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The University of Birmingham is a public research university located in Edgbaston, Birmingham, United Kingdom. It is a member of both the Russell Group of British research universities and the international network of research universities, Universitas 21. The university was ranked 15th in the UK and 82nd in the world in the QS World University Rankings for 2016-17, in 2013, Birmingham was named University of the Year 2014 in the Times Higher Education awards. The 2016 Global Employability University Ranking places Birmingham at 90th world-wide, Birmingham is also ranked 9th in the UK for Graduate Prospects in The Times and The Sunday Times Good University Guide 2017. The student population includes 21,495 undergraduate and 12,335 postgraduate students, the annual income of the institution for 2015–16 was £625.6 million of which £135.5 million was from research grants and contracts, with an expenditure of £562.1 million. Academics and alumni of the university include former British Prime Ministers Neville Chamberlain, and Stanley Baldwin and these classes were the first ever held outside London or south of the Scottish border in the winter of 1767–68. The first clinical teaching was undertaken by medical and surgical apprentices at the General Hospital, the medical school which grew out of the Birmingham Workhouse Infirmary was founded in 1828 but Cox began teaching in December 1825. Queen Victoria granted her patronage to the Clinical Hospital in Birmingham and it was the first provincial teaching hospital in England. In 1843, the college became known as Queens College. The college was founded in 1875 and it was this institution that would eventually form the nucleus of the University of Birmingham. In 1882, the Departments of Chemistry, Botany and Physiology were transferred to Mason Science College, soon followed by the Departments of Physics and Comparative Anatomy. The transfer of the Medical School to Mason Science College gave considerable impetus to the importance of that college. As the result of the Mason University College Act 1897 it became incorporated as Mason University College on 1 January 1898 and it was largely due to Chamberlains enthusiasm that the university was granted a royal charter by Queen Victoria on 24 March 1900. The Calthorpe family offered twenty-five acres of land on the Bournbrook side of their estate in July, the Court of Governors received the Birmingham University Act 1900, which put the royal charter into effect on 31 May. Birmingham was therefore arguably the first so-called red brick university, although several other universities claim this title, the transfer of Mason University College to the new University of Birmingham, with Chamberlain as its first chancellor and Sir Oliver Lodge as the first principal, was complete. All that remained of Josiah Masons legacy was his Mermaid in the chief of the university shield and of his college. It became the first civic and campus university in England, consequently, the faculty, the first of its kind in Britain, was founded by Sir William Ashley in 1901, who from 1902 until 1923 served as first Professor of Commerce and Dean of the Faculty. From 1905 to 1908, Edward Elgar held the position of Peyton Professor of Music at the university and he was succeeded by his friend Granville Bantock
24.
Kilowatt
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The watt is a derived unit of power in the International System of Units defined as 1 joule per second and can be used to quantify the rate of energy transfer. Power has dimensions of M L2 T −3, when an objects velocity is held constant at one meter per second against constant opposing force of one newton the rate at which work is done is 1 watt. 1 W =1 V ⋅ A Two additional unit conversions for watt can be using the above equation. 1 W =1 V2 Ω =1 A2 ⋅ Ω Where ohm is the SI derived unit of electrical resistance, a person having a mass of 100 kilograms who climbs a 3-meter-high ladder in 5 seconds is doing work at a rate of about 600 watts. Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power. A laborer over the course of an 8-hour day can sustain an output of about 75 watts, higher power levels can be achieved for short intervals. The watt is named after the Scottish scientist James Watt for his contributions to the development of the steam engine, in 1960 the 11th General Conference on Weights and Measures adopted it for the measurement of power into the International System of Units. For additional examples of magnitude for multiples and submultiples of the watt, technologically important powers that are measured in femtowatts are typically found in reference to radio and radar receivers. For example, meaningful FM tuner performance figures for sensitivity, quieting and these input levels are often stated in dBf. This is 0.2739 microvolt across a 75-ohm load or 0.5477 microvolt across a 300-ohm load, the picowatt is equal to one trillionth of a watt. Technologically important powers that are measured in picowatts are typically used in reference to radio and radar receivers, acoustics, the nanowatt is equal to one billionth of a watt. Important powers that are measured in nanowatts are also used in reference to radio. The microwatt is equal to one millionth of a watt, compact solar cells for devices such as calculators and watches are typically measured in microwatts. The milliwatt is equal to one thousandth of a watt, a typical laser pointer outputs about five milliwatts of light power, whereas a typical hearing aid for people uses less than one milliwatt. Audio signals and other electronic signal levels are measured in dBm. The kilowatt is equal to one thousand watts and this unit is typically used to express the output power of engines and the power of electric motors, tools, machines, and heaters. It is also a unit used to express the electromagnetic power output of broadcast radio. One kilowatt is equal to 1.34 horsepower
25.
Radar
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Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the objects location and speed. Radar was developed secretly for military use by several nations in the period before, the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging. The term radar has since entered English and other languages as a common noun, high tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Other systems similar to make use of other parts of the electromagnetic spectrum. One example is lidar, which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves, as early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, an instructor at the Imperial Russian Navy school in Kronstadt. The next year, he added a spark-gap transmitter, in 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, the German inventor Christian Hülsmeyer was the first to use radio waves to detect the presence of distant metallic objects. In 1904, he demonstrated the feasibility of detecting a ship in dense fog and he obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23,1904 for a radar system. It operated on a 50 cm wavelength and the radar signal was created via a spark-gap. In 1915, Robert Watson-Watt used radio technology to advance warning to airmen. Watson-Watt became an expert on the use of direction finding as part of his lightning experiments. As part of ongoing experiments, he asked the new boy, Arnold Frederic Wilkins, Wilkins made an extensive study of available units before selecting a receiver model from the General Post Office. Its instruction manual noted that there was fading when aircraft flew by, in 1922, A. Hoyt Taylor and Leo C. Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, eight years later, Lawrence A. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war. Hugon, began developing a radio apparatus, a part of which was installed on the liner Normandie in 1935
26.
Allies of World War II
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The Allies of World War II, called the United Nations from the 1 January 1942 declaration, were the countries that together opposed the Axis powers during the Second World War. The Allies promoted the alliance as seeking to stop German, Japanese, at the start of the war on 1 September 1939, the Allies consisted of France, Poland and the United Kingdom, and dependent states, such as the British India. Within days they were joined by the independent Dominions of the British Commonwealth, Australia, Canada, New Zealand, Poland was a minor factor after its defeat in 1939, France was a minor factor after its defeat in 1940. China had already been into a war with Japan since the Marco Polo Bridge Incident of 1937. The alliance was formalised by the Declaration by United Nations, from 1 January 1942, however, the name United Nations was rarely used to describe the Allies during the war. The leaders of the Big Three – the UK, the Soviet Union, in 1945, the Allied nations became the basis of the United Nations. The origins of the Allied powers stem from the Allies of World War I, Germany resented signing Treaty of Versailles. The new Weimar republics legitimacy became shaken, by the early 1930s, the Nazi Party led by Adolf Hitler became the dominant revanchist movement in Germany and Hitler and the Nazis gained power in 1933. The Nazi regime demanded the cancellation of the Treaty of Versailles and made claims to German-populated Austria. The likelihood of war was high, and the question was whether it could be avoided through strategies such as appeasement, in Asia, when Japan seized Manchuria in 1931, the League of Nations condemned it for aggression against China. Japan responded by leaving the League of Nations in March 1933, after four quiet years, the Sino-Japanese War erupted in 1937 with Japanese forces invading China. The League of Nations condemned Japans actions and initiated sanctions on Japan, the United States, in particular, was angered at Japan and sought to support China. In March 1939, Germany took over Czechoslovakia, violating the Munich Agreement signed six months before, Britain and France decided that Hitler had no intention to uphold diplomatic agreements and responded by preparing for war. On 31 March 1939, Britain formed the Anglo-Polish military alliance in an effort to avert a German attack on the country, also, the French had a long-standing alliance with Poland since 1921. The Soviet Union sought an alliance with the powers. The agreement secretly divided the independent nations of eastern Europe between the two powers and assured adequate oil supplies for the German war machine, on 1 September 1939, Germany invaded Poland, two days later Britain and France declared war on Germany. Then, on 17 September 1939, the Soviet Union invaded Poland from the east, a Polish government-in-exile was set up and it continued to be one of the Allies, a model followed by other occupied countries. After a quiet winter, Germany in April 1940 invaded and quickly defeated Denmark, Norway, Belgium, Britain and its Empire stood alone against Hitler and Mussolini
27.
Clutter (radar)
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Clutter is a term used for unwanted echoes in electronic systems, particularly in reference to radars. Such echoes are returned from ground, sea, rain, animals/insects, chaff and atmospheric turbulences. What one person considers to be clutter, another may consider to be a target, however, targets usually refer to point scatterers and clutter to extended scatterers. The clutter may fill a volume or be confined to a surface, in addition to any possible clutter there will also always be noise. The total signal competing with the return is thus clutter plus noise. In practice there is either no clutter or clutter dominates. In the first case the radar is said to be Noise Limited, rain, hail, snow and chaff are examples of volume clutter. For example, suppose an airborne target, at range R, is within a rainstorm, what is the effect on the detectability of the target. First find the magnitude of the clutter return, assume that the clutter fills the cell containing the target, that scatterers are statistically independent and that the scatterers are uniformly distributed through the volume. The clutter volume illuminated by a pulse can be calculated from the beam widths, the azimuth and elevation beamwidths, at a range R, are θ /2 and ϕ /2 respectively if the illuminated cell is assumed to have an elliptical cross section. In practice the beam shape will approximate to a function which itself approximates to a Gaussian function. The correction factor is found by integrating across the width the Gaussian approximation of the antenna. The corrected back scattered power is C = P t G t A r 2 log 22 R4 π4 η A number of simpliflying substitutions can be made, halving the distance will cause the signal to noise ratio to increase by a factor of 16. When the radar is volume clutter limited, however, the variation is a square law. If pulse compression is used then the pulse duration to be used in the calculation is that of the compressed pulse. Consider a beam 10° in elevation, at a range of 10 km the beam could cover from ground level to a height of 1750 metres. There could be rain at ground level but the top of the beam could be above cloud level, in the part of the beam containing rain the rainfall rate will not be constant. One would need to know how the rain was distributed to make any assessment of the clutter
28.
Microwave oven
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A microwave oven is a kitchen appliance that heats and cooks food by exposing it to microwave radiation in the electromagnetic spectrum. This induces polar molecules in the food to rotate and produce energy in a process known as dielectric heating. Percy Spencer is generally credited with inventing the microwave oven after World War II from radar technology developed during the war. Named the Radarange, it was first sold in 1946, Raytheon later licensed its patents for a home-use microwave oven that was first introduced by Tappan in 1955, but these units were still too large and expensive for general home use. The countertop microwave oven was first introduced in 1967 by the Amana Corporation, Microwave ovens are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for heating of otherwise slowly prepared cooking items, such as hot butter, fats. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, exceptions occur in rare cases where the oven is used to heat frying-oil and other very oily items, which attain far higher temperatures than that of boiling water. Some modern microwave ovens are part of units with built-in extractor hoods. The exploitation of high-frequency radio waves for heating substances was possible by the development of vacuum tube radio transmitters around 1920. By 1930 the application of waves to heat human tissue had developed into the medical therapy of diathermy. At the 1933 Chicago Worlds Fair, Westinghouse demonstrated the cooking of foods between two metal plates attached to a 10 kW,60 MHz shortwave transmitter. The Westinghouse team, led by I. F. Mouromtseff, found that foods like steaks and this patent proposed radio frequency heating, at 10 to 20 megahertz. The invention of the cavity magnetron made possible the production of waves of a small enough wavelength. The magnetron was originally a component in the development of short wavelength radar during World War II. A more high-powered microwave generator that worked at shorter wavelengths was needed, sir Henry Tizard travelled to the U. S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help. An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, contracts were awarded to Raytheon and other companies for mass production of the magnetron. In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer. Employed by Raytheon at the time, he noticed that microwaves from a radar set he was working on started to melt a candy bar he had in his pocket
29.
Cathode
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A cathode is the electrode from which a conventional current leaves a polarized electrical device. A conventional current describes the direction in which positive electronic charges move, Electrons have a negative charge, so the movement of electrons is opposite to the conventional current flow. Consequently, the mnemonic cathode current departs also means that flow into the devices cathode. Cathode polarity with respect to the anode can be positive or negative and this outward current is carried internally by positive ions moving from the electrolyte to the positive cathode. It is continued externally by electrons moving inwards, this negative charge moving inwards constituting positive current flowing outwards, for example, the Daniell galvanic cells copper electrode is the positive terminal and the cathode. In a recharging battery, or an electrolytic cell performing electrolysis, for example, reversing the current direction in a Daniell galvanic cell would produce an electrolytic cell, where the copper electrode is the positive terminal and the anode. In a diode, the cathode is the terminal at the pointed end of the arrow symbol. Note, electrode naming for diodes is always based on the direction of the forward current, an electrode through which current flows the other way is termed an anode. The use of West to mean the out direction may appear unnecessarily contrived, previously, as related in the first reference cited above, Faraday had used the more straightforward term exode. The reference he used to effect was the Earths magnetic field direction. The flow of electrons is almost always from anode to cathode outside of the cell or device, regardless of the cell or device type, an exception is when a diode reverse-conducts, either by accident or by design. In chemistry, a cathode is the electrode of a cell at which reduction occurs. Another mnemonic is to note the cathode has a c, as does reduction, perhaps most useful would be to remember cathode corresponds to cation and anode corresponds to anion. The cathode can be negative like when the cell is electrolytic, the cathode supplies electrons to the positively charged cations which flow to it from the electrolyte. The cathodic current, in electrochemistry, is the flow of electrons from the interface to a species in solution. The anodic current is the flow of electrons into the anode from a species in solution, in an electrolytic cell, the cathode is where the negative polarity is applied to drive the cell. Common results of reduction at the cathode are hydrogen gas or pure metal from metal ions, when discussing the relative reducing power of two redox agents, the couple for generating the more reducing species is said to be more cathodic with respect to the more easily reduced reagent. When metal ions are reduced from ionic solution, they form a metal surface on the cathode
30.
Anode
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An anode is an electrode through which conventional current flows into a polarized electrical device. A common mnemonic is ACID for anode current into device, the direction of electric current is opposite to the direction of electron flow, electrons flow out the anode to the outside circuit. The terms anode and cathode do not relate to the polarity of those electrodes but the direction of the current. Conventional current quantifies the flow of positive charge, in most cases, positive charge leaves the device via the cathode, and positive charge flows into the device via the anode. Conventional current depends not only on the direction the charge carriers move, the currents outside the device are usually carried by electrons in a metal conductor. The flow of electrons is opposite to conventional current because electrons have a negative charge, consequently, electrons leave the device via the anode, and electrons enter the device through the cathode. The anode and cathode have slightly different definitions for electrical devices such as diodes and vacuum tubes where the naming is fixed. These devices usually allow substantial current flow in one direction but negligible current in the other direction, consequently, the electrode names use the terms that have substantial ordinary currents. An ideal diode allows current in one direction but not in the other, for the ideal diode, it makes sense to always call that terminal the anode. For non-ideal diodes, the electrodes are also given fixed names even though such a diode under reverse bias would have a positive charge out of the anode. For some operating conditions and devices, such as diode breakdown, Zener diodes, or photodiodes, the polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. This inward current is carried externally by electrons moving outwards, negative charge flowing in one direction being electrically equivalent to positive charge flowing in the opposite direction. In a recharging battery, or a cell, the anode is the positive terminal. In a diode, the anode is the terminal at the tail of the arrow symbol. Note electrode naming for diodes is always based on the direction of the forward current, in a cathode ray tube, the anode is the positive terminal where electrons flow out of the device, i. e. where positive electric current flows in. The use of East to mean the in direction may appear contrived, previously, as related in the first reference cited above, Faraday had used the more straightforward term eisode. The reference he used to effect was the Earths magnetic field direction. In electrochemistry, the anode is where oxidation occurs and is the positive polarity contact in an electrolytic cell, at the anode, anions are forced by the electrical potential to react chemically and give off electrons which then flow up and into the driving circuit
31.
Control grid
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The control grid is an electrode used in amplifying thermionic valves such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode electrode. The control grid usually consists of a screen or helix of fine wire surrounding the cathode. The control grid was invented by Lee De Forest, who in 1906 added a grid to the Fleming valve to create the first amplifying vacuum tube, the Audion. In a valve, the hot cathode emits negatively charged electrons, which are attracted to and captured by the anode, the control grid between the cathode and anode functions as a gate to control the current of electrons reaching the anode. A more negative voltage on the grid will repel the electrons back toward the cathode so fewer get through to the anode, a less negative, or positive, voltage on the grid will allow more electrons through, increasing the anode current. A relatively small variation in voltage on the grid causes a significantly large variation in anode current. The presence of a resistor in the anode circuit causes a variation in voltage to appear at the anode. The variation in voltage can be much larger than the variation in grid voltage which caused it. The grid in the first triode valve consisted of a piece of wire placed between the filament and the anode. This quickly evolved into a helix or cylindrical screen of fine wire placed between a single strand filament and a cylindrical anode, the grid is usually made of a very thin wire that can resist high temperatures and is not prone to emitting electrons itself. Molybdenum alloy with a gold plating is frequently used and it is wound on soft copper sideposts, which are swaged over the grid windings to hold them in place. A 1950s variation is the grid, which winds very fine wire onto a rigid stamped metal frame. This allows the holding of very close tolerances, so the grid can be placed closer to the filament, by placing the control grid closer to the filament/cathode relative to the anode, a greater amplification results. This degree of amplification is referred to in valve data sheets as the amplification factor and it also results in higher transconductance, which is a measure of the anode current change versus grid voltage change. The noise figure of a valve is inversely proportional to its transconductance, lower noise can be very important when designing a radio or television receiver. A valve can contain more than one control grid, the hexode contains two such grids, one for a received signal and one for the signal from a local oscillator. The valves inherent non-linearity causes not only both original signals to appear in the circuit, but also the sum and difference of those signals. This can be exploited as a frequency-changer in superheterodyne receivers, a variation of the control grid is to produce the helix with a variable pitch
32.
Triode
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A triode is an electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope, a heated filament or cathode, a grid, and a plate. Its invention founded the electronics age, making possible amplified radio technology, triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters, in recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who prefer its sound. The name triode was coined by British physicist William Eccles sometime around 1920, derived from the Greek τρίοδος, tríodos, from tri- and hodós, originally meaning the place where three roads meet. The first vacuum tube used in radio was the thermionic diode or Fleming valve and it was an evacuated glass bulb containing two electrodes, a heated filament and a plate. Von Liebens partially-evacuated three-element tube, patented in March 1906, contained a trace of mercury vapor and was intended to amplify weak telephone signals. Starting in October 1906 De Forest patented a number of three-element tube designs by adding an electrode to the diode, the one which became the design of the triode, in which the grid was located between the filament and plate, was patented January 29,1907. Like the von Lieben vacuum tube, De Forests Audions were incompletely evacuated and contained some gas at low pressure, von Liebens vacuum tube did not see much development due to his death 7 years after he invented it at the outbreak of World War I. The many uses for amplification motivated its rapid development, the name triode appeared later, when it became necessary to distinguish it from other kinds of vacuum tubes with more or fewer elements. There were lengthy lawsuits between De Forest and von Lieben, and De Forest and the Marconi Company, representing John Ambrose Fleming the inventor of the diode. The discovery of the amplifying ability in 1912 revolutionized electrical technology, creating the new field of electronics. The triode was immediately applied to areas of communication. Triode continuous wave radio transmitters replaced the cumbersome inefficient damped wave spark gap transmitters, amplifying triode radio receivers, which had the power to drive loudspeakers, replaced weak crystal radios, which had to be listened to with earphones, allowing families to listen together. This resulted in the evolution of radio from a commercial service to the first mass communication medium. Triodes made transcontinental telephone service possible, vacuum tube triode repeaters, invented at Bell Telephone after its purchase of the Audion rights, allowed telephone calls to travel beyond the unamplified limit of about 800 miles. The opening by Bell of the first transcontinental telephone line was celebrated 3 years later, other inventions made possible by the triode were television, public address systems, electric phonographs, and talking motion pictures. The triode served as the base from which later vacuum tubes developed, such as the tetrode and pentode. Today triodes are used in high-power applications for which solid state semiconductor devices are unsuitable, such as radio transmitters
33.
Lee de Forest
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Lee de Forest was an American inventor, self-described Father of Radio, and a pioneer in the development of sound-on-film recording used for motion pictures. He had over 180 patents, but also a tumultuous career—he boasted that he made, then lost and he was also involved in several major patent lawsuits, spent a substantial part of his income on legal bills, and was even tried for mail fraud. His most famous invention, in 1906, was the three-element Audion vacuum tube, Lee de Forest was born in 1873 in Council Bluffs, Iowa, the son of Anna Margaret and Henry Swift DeForest. He was a descendant of Jessé de Forest, the leader of a group of Walloon Huguenots who fled Europe in the 17th Century due to religious persecution. De Forests father was a Congregational Church minister who hoped his son would become a pastor. De Forest prepared for college by attending Mount Hermon Boys School in Mount Hermon, after completing his undergraduate studies, in September,1896 de Forest began three years of postgraduate work. However, his experiments had a tendency to blow fuses. Even after being warned to be careful, he managed to douse the lights during an important lecture by Professor Charles Hastings. One drawback to Marconis approach was his use of a coherer as a receiver, which, while providing for permanent records, was slow, insensitive. After making unsuccessful inquiries about employment with Nikola Tesla and Marconi and his first job after leaving Yale was with the Western Electric Companys telephone lab in Chicago, Illinois. While there he developed his first receiver, which was based on findings by two German scientists, Drs. A. Neugschwender and Emil Aschkinass and their original design consisted of a mirror in which a narrow, moistened slit had been cut through the silvered back. Attaching a battery and telephone receiver, they could hear sound changes in response to radio signal impulses, De Forest, along with Ed Smythe, a co-worker who provided financial and technical help, developed variations they called responders. With radio research his main priority, de Forest next took a teaching position at the Lewis Institute. By 1900, using a transmitter and his responder receiver. Professor Clarence Freeman of the Armour Institute became interested in de Forests work, Marconi had already made arrangements to provide reports for the Associated Press, which he had successfully done for the 1899 contest. De Forest contracted to do the same for the smaller Publishers Press Association, the race effort turned out to be an almost total failure. The Freeman transmitter broke down — in a fit of rage, none of these companies had effective tuning for their transmitters, so only one could transmit at a time without causing mutual interference. De Forest ruefully noted that under conditions the only successful wireless communication was done by visual semaphore wig-wag flags
34.
Horseshoe magnet
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A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet, a force that pulls on other materials, such as iron. A permanent magnet is a made from a material that is magnetized. An everyday example is a refrigerator used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are attracted to a magnet, are called ferromagnetic. These include iron, nickel, cobalt, some alloys of rare-earth metals, ferromagnetic materials can be divided into magnetically soft materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically hard materials, which do. To demagnetize a saturated magnet, a magnetic field must be applied. Hard materials have high coercivity, whereas soft materials have low coercivity, an electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of soft material such as steel. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the local strength of magnetism in a material is measured by its magnetization. Ancient people learned about magnetism from lodestones, which are naturally magnetized pieces of iron ore, the word magnet in Greek meant stone from Magnesia, a part of ancient Greece where lodestones were found. Lodestones, suspended so they could turn, were the first magnetic compasses, the earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia, by the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. The magnetic flux density is a vector field, the magnetic B field vector at a given point in space is specified by two properties, Its direction, which is along the orientation of a compass needle. Its magnitude, which is proportional to how strongly the compass needle orients along that direction, in SI units, the strength of the magnetic B field is given in teslas. A magnets magnetic moment is a vector that characterizes the overall magnetic properties. For a bar magnet, the direction of the moment points from the magnets south pole to its north pole. In SI units, the moment is specified in terms of A·m2
35.
Fleming's left-hand rule for motors
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Flemings left-hand rule for motors is one of a pair of visual mnemonics, the other being Flemings right-hand rule. When current flows in a wire, and a magnetic field is applied across that flow. A left hand can be held, as shown in the illustration, each finger is then assigned to a quantity. The right and left hand are used for generators and motors respectively, several memory aids have been used in order to remember the quantity each finger represents. Van de Graaffs translation of Flemings rules is the FBI rule, the F represents the direction of Force of the conductor The B represents the direction of the Magnetic field The I represents the direction of the Current. This uses the conventional symbolic parameters of F, B and I, the thumb is the force, F The first finger is the magnetic flux density, B The second finger is the electric current, I. Of course, if the mnemonic is taught with a different arrangement of the parameters to the fingers and these variants are catalogued more fully on the FBI mnemonics page. Flemings left-hand rule is used for motors, while Flemings right-hand rule is used for electric generators. Different hands need to be used for motors and generators because of the differences between cause and effect, in an electric motor, the electric current and magnetic field exist, and they lead to the force that creates the motion, and so the left hand rule is used. In an electric generator, the motion and magnetic field exist, and they lead to the creation of the electric current, to illustrate why, consider that many types of electric motors can also be used as electric generators. A vehicle powered by such a motor can be accelerated up to speed by connecting the motor to a fully charged battery. If the motor is disconnected from the fully charged battery, and connected instead to a completely flat battery. The motor will act as a generator and convert the kinetic energy back to electrical energy. Since neither the direction of motion nor the direction of the field has changed. This follows from the law of thermodynamics. The rule for motors can be recalled by remembering that motors drive on the left in Britain, the rule for generators can be recalled by remembering that either the letters g and r is common to both right and generator, or the phrase Jenny is always right. When electrons, or any charged particles, flow in the direction they generate a cylindrical magnetic field that wraps round the conductor. The direction of the magnetic field is sometimes remembered by Maxwells corkscrew rule
36.
Electromagnet
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An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. The magnetic field disappears when the current is turned off, electromagnets usually consist of insulated wire wound into a coil. A current through the wire creates a field which is concentrated in the hole in the center of the coil. The main advantage of an electromagnet over a permanent magnet is that the field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a supply of current to maintain the magnetic field. Electromagnets are also employed in industry for picking up and moving heavy objects such as scrap iron. Danish scientist Hans Christian Ørsted discovered in 1820 that electric currents create magnetic fields, british scientist William Sturgeon invented the electromagnet in 1824. His first electromagnet was a piece of iron that was wrapped with about 18 turns of bare copper wire. The iron was varnished to insulate it from the windings, when a current was passed through the coil, the iron became magnetized and attracted other pieces of iron, when the current was stopped, it lost magnetization. Sturgeon displayed its power by showing that although it only weighed seven ounces, however, Sturgeons magnets were weak because the uninsulated wire he used could only be wrapped in a single spaced out layer around the core, limiting the number of turns. Beginning in 1830, US scientist Joseph Henry systematically improved and popularized the electromagnet, the first major use for electromagnets was in telegraph sounders. A portative electromagnet is one designed to just hold material in place, a tractive electromagnet applies a force and moves something. The solenoid is a coil of wire, and the plunger is made of a such as soft iron. Applying a current to the solenoid applies a force to the plunger, the plunger stops moving when the forces upon it are balanced. For example, the forces are balanced when the plunger is centered in the solenoid, the maximum uniform pull happens when one end of the plunger is at the middle of the solenoid. For units using inches, pounds force, and amperes with long, slender, solenoids, for example, a 12-inch long coil with a long plunger of 1-square inch cross section and 11,200 ampere-turns had a maximum pull of 8.75 pounds. The maximum pull is increased when a stop is inserted into the solenoid. The stop becomes a magnet that will attract the plunger, it adds little to the pull when the plunger is far away
37.
Hysteresis
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Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a magnetic field. Plots of a component of the moment often form a loop or hysteresis curve. This history dependence is the basis of memory in a disk drive. Hysteresis occurs in ferromagnetic and ferroelectric materials, as well as in the deformation of rubber bands and shape-memory alloys, in natural systems it is often associated with irreversible thermodynamic change such as phase transitions and with internal friction, and dissipation is a common side effect. Hysteresis can be found in physics, chemistry, engineering, biology and economics and it is incorporated in many artificial systems, for example, in thermostats and Schmitt triggers, it prevents unwanted frequent switching. Hysteresis can be a lag between an input and an output that disappears if the input is varied more slowly, this is known as rate-dependent hysteresis. However, phenomena such as the magnetic hysteresis loops are mainly rate-independent, systems with hysteresis are nonlinear, and can be mathematically challenging to model. The term hysteresis is derived from ὑστέρησις, an ancient Greek word meaning deficiency or lagging behind and it was coined around 1890 by Sir James Alfred Ewing to describe the behaviour of magnetic materials. Some early work on describing hysteresis in mechanical systems was performed by James Clerk Maxwell, subsequently, hysteretic models have received significant attention in the works of Ferenc Preisach, Louis Néel and D. H. Everett in connection with magnetism and absorption. A more formal theory of systems with hysteresis was developed in the 1970s by a group of Russian mathematicians led by Mark Krasnoselskii. One type of hysteresis is a lag between input and output. A simple example is a sinusoidal input X that results in a sinusoidal output Y and this kind of hysteresis is often referred to as rate-dependent hysteresis. If the input is reduced to zero, the continues to respond for a finite time. This constitutes a memory of the past, but a limited one because it disappears as the output decays to zero, the phase lag depends on the frequency of the input, and goes to zero as the frequency decreases. When rate-dependent hysteresis is due to effects like friction, it is associated with power loss. Systems with rate-independent hysteresis have a persistent memory of the past that remains after the transients have died out, the future development of such a system depends on the history of states visited, but does not fade as the events recede into the past. If an input variable X cycles from X0 to X1 and back again, the values of Y depend on the path of values that X passes through but not on the speed at which it traverses the path
38.
High frequency
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High frequency is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 MHz. It is also known as the band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency, while the band of higher frequencies is known as the very high frequency band. The HF band is a part of the shortwave band of frequencies. The band is used by shortwave broadcasting stations, aviation communication, government time stations, weather stations, amateur radio and citizens band services. By this method HF radio waves can travel beyond the horizon, around the curve of the Earth and it depends on the angle of incidence of the waves, it is lowest when the waves are directed straight upwards, and is higher with less acute angles. This means that at longer distances, where the waves graze the ionosphere at a blunt angle. The lowest usable frequency depends on the absorption in the layer of the ionosphere. This absorption is stronger at low frequencies and is stronger with increased solar activity. When all factors are at their optimum, worldwide communication is possible on HF, at many other times it is possible to make contact across and between continents or oceans. At worst, when a band is dead, no communication beyond the limited groundwave paths is possible no matter what powers, on such an open band, interference originating over a wide area affects many potential users. These issues are significant to military, safety and amateur radio users of the HF bands, other standards development such as STANAG5066 provides for error free data communications through the use of ARQ protocols. Noise, especially man-made interference from devices, tends to have a great effect on the HF bands. In recent years, concerns have risen among certain users of the HF spectrum over broadband over power lines Internet access and this is due to the frequencies on which BPL operates and the tendency for the BPL signal to leak from power lines. Some BPL providers have installed notch filters to block out certain portions of the spectrum, other electronic devices including plasma televisions can also have a detrimental effect on the HF spectrum. In aviation, HF communication systems are required for all trans-oceanic flights and these systems incorporate frequencies down to 2 MHz to include the 2182 kHz international distress and calling channel. The upper section of HF shares many characteristics with the part of VHF. The parts of this section not allocated to radio are used for local communications
39.
Very high frequency
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Very high frequency is the ITU designation for the range of radio frequency electromagnetic waves from 30 MHz to 300 MHz, with corresponding wavelengths of ten to one meters. Frequencies immediately below VHF are denoted high frequency, and the higher frequencies are known as ultra high frequency. Air traffic control communications and air navigation systems work at distances of 100 kilometres or more to aircraft at cruising altitude, some older DVB-T receivers included channels E2 to E4 but newer ones only go down to channel E5. VHF propagation characteristics are suited for terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter. VHF waves are restricted to the radio horizon less than 100 miles. VHF is less affected by noise and interference from electrical equipment than lower frequencies. Unlike high frequencies, the ionosphere does not usually reflect VHF waves, the distance to the radio horizon is slightly extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere. These approximations are only valid for antennas at heights that are compared to the radius of the Earth. They may not necessarily be accurate in mountainous areas, since the landscape may not be transparent enough for radio waves, in engineered communications systems, more complex calculations are required to assess the probable coverage area of a proposed transmitter station. The accuracy of calculations for digital TV signals is being debated. Portable radios usually use whips or rubber ducky antennas, while base stations usually use larger fiberglass whips or collinear arrays of vertical dipoles, for directional antennas, the Yagi antenna is the most widely used as a high gain or beam antenna. For television reception, the Yagi is used, as well as the log periodic antenna due to its wider bandwidth, helical and turnstile antennas are used for satellite communication since they employ circular polarization. For even higher gain, multiple Yagis or helicals can be mounted together to make array antennas, vertical collinear arrays of dipoles can be used to make high gain omnidirectional antennas, in which more of the antennas power is radiated in horizontal directions. Television and FM broadcasting stations use arrays of specialized dipole antennas such as batwing antennas. Certain subparts of the VHF band have the same use around the world, some national uses are detailed below. 108–118 MHz, Air navigation beacons VOR and Instrument Landing System localiser, 118–137 MHz, Airband for air traffic control, AM,121.5 MHz is emergency frequency 144–146 MHz, Amateur radio. Other capital cities and regional areas used a combination of these, the initial commercial services in Hobart and Darwin were respectively allocated channels 6 and 8 rather than 7 or 9. By the early 1960s it became apparent that the 10 VHF channels were insufficient to support the growth of television services and this was rectified by the addition of three additional frequencies—channels 0, 5A and 11
40.
Magnet
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A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet, a force that pulls on other materials, such as iron. A permanent magnet is a made from a material that is magnetized. An everyday example is a refrigerator used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are attracted to a magnet, are called ferromagnetic. These include iron, nickel, cobalt, some alloys of rare-earth metals, ferromagnetic materials can be divided into magnetically soft materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically hard materials, which do. To demagnetize a saturated magnet, a magnetic field must be applied. Hard materials have high coercivity, whereas soft materials have low coercivity, an electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of soft material such as steel. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the local strength of magnetism in a material is measured by its magnetization. Ancient people learned about magnetism from lodestones, which are naturally magnetized pieces of iron ore, the word magnet in Greek meant stone from Magnesia, a part of ancient Greece where lodestones were found. Lodestones, suspended so they could turn, were the first magnetic compasses, the earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia, by the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. The magnetic flux density is a vector field, the magnetic B field vector at a given point in space is specified by two properties, Its direction, which is along the orientation of a compass needle. Its magnitude, which is proportional to how strongly the compass needle orients along that direction, in SI units, the strength of the magnetic B field is given in teslas. A magnets magnetic moment is a vector that characterizes the overall magnetic properties. For a bar magnet, the direction of the moment points from the magnets south pole to its north pole. In SI units, the moment is specified in terms of A·m2
41.
Resonator
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The oscillations in a resonator can be either electromagnetic or mechanical. Resonators are used to generate waves of specific frequencies or to select specific frequencies from a signal. Musical instruments use acoustic resonators that produce sound waves of specific tones, another example is quartz crystals used in electronic devices such as radio transmitters and quartz watches to produce oscillations of very precise frequency. A cavity resonator is one in which waves exist in a space inside the device. Acoustic cavity resonators, in sound is produced by air vibrating in a cavity with one opening, are known as Helmholtz resonators. A physical system can have as many resonant frequencies as it has degrees of freedom, systems with one degree of freedom, such as a mass on a spring, pendulums, balance wheels, and LC tuned circuits have one resonant frequency. Systems with two degrees of freedom, such as coupled pendulums and resonant transformers can have two resonant frequencies, a crystal lattice composed of N atoms bound together can have N resonant frequencies. As the number of coupled harmonic oscillators grows, the time it takes to transfer energy from one to the next becomes significant, the vibrations in them begin to travel through the coupled harmonic oscillators in waves, from one oscillator to the next. The term resonator is most often used for an object in which vibrations travel as waves, at an approximately constant velocity, bouncing back. The material of the resonator, through which the waves flow, therefore, they can have millions of resonant frequencies, although only a few may be used in practical resonators. The oppositely moving waves interfere with other, and at its resonant frequencies reinforce each other to create a pattern of standing waves in the resonator. If the distance between the sides is d, the length of a trip is 2 d. To cause resonance, the phase of a sinusoidal wave after a round trip must be equal to the initial phase so the waves self-reinforce. The above analysis assumes the medium inside the resonator is homogeneous, so the waves travel at a constant speed, and they are then called overtones instead of harmonics. There may be several such series of resonant frequencies in a single resonator, an electrical circuit composed of discrete components can act as a resonator when both an inductor and capacitor are included. Oscillations are limited by the inclusion of resistance, either via a specific resistor component, such resonant circuits are also called RLC circuits after the circuit symbols for the components. A distributed-parameter resonator has capacitance, inductance, and resistance that cannot be isolated into separate lumped capacitors, inductors, an example of this, much used in filtering, is the helical resonator. A single layer coil that is used as a secondary or tertiary winding in a Tesla coil or magnifying transmitter is also a distributed resonator
42.
Revolver
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A revolver is a repeating handgun that has a revolving cylinder containing multiple chambers and at least one barrel for firing. Revolvers might be regarded as a subset of pistols, or as a subset of handguns. Though the term revolver usually only refers to handguns, other firearms may also have a revolving chamber and these include some models of grenade launchers, shotguns, and rifles. Most revolvers contain five or six rounds in the cylinder, though the original name was revolving gun, the short-hand revolver is universally used. The revolver allows the user to fire multiple rounds without reloading, each time the user cocks the hammer, the cylinder revolves to align the next chamber and round with the hammer and barrel, which gives this type of firearm its name. In a single-action revolver, the user pulls the back with his free hand or thumb. In a double-action revolver, pulling the trigger moves the back, then releases it. Loading and unloading a double-action revolver requires the operator to swing out the cylinder and insert the proper ammunition, the first guns with multichambered cylinders that revolved to feed one barrel were made in the late 16th century in Europe. They were expensive and rare curiosities, not until the 19th century would revolvers become common weapons of industrial production. One of the first was a flintlock revolver patented by Elisha Collier in 1814, the first percussion revolver was made by Lenormand of Paris in 1820 and the first percussion cap revolver was invented by the Italian Francesco Antonio Broccu in 1833. He received a prize of 300 francs for his invention, although he did not patent it, however, in 1835 a similar handgun was patented by Samuel Colt, who would go on to make the first mass-produced revolver. The first cartridge revolvers were produced around 1854 by Eugene Lefaucheux, revolvers soon became standard for nearly all uses. In the early 20th century, semi-automatic pistols were developed, which can hold more rounds, Automatic pistols also have a flat profile, more suitable for concealed carry. Automatic pistols have almost completely replaced revolvers in military and law enforcement use, revolvers still remain popular as back-up and off-duty handguns among American law enforcement officers and security guards. Also, revolvers are still common in the American private sector as defensive, in the development of firearms, an important limiting factor was the time it took to reload the weapon after it was fired. While the user was reloading, the weapon was useless, several approaches to the problem of increasing the rate of fire were developed, the earliest being multi-barrelled weapons which allowed two or more shots without reloading. Later weapons featured multiple barrels revolving along a single axis, the earliest examples of what today is called a revolver were made in Germany in the late 16th century. These weapons featured a barrel with a revolving cylinder holding the powder
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Colt's Manufacturing Company
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Colts Manufacturing Company is an American firearms manufacturer, founded in 1855 by Samuel Colt. It is the corporation to Colts earlier firearms-making efforts, which started in 1836. Colts earliest designs played a role in the popularization of the revolver. Although Samuel Colt did not invent the concept, his designs resulted in the first very successful ones. The most famous Colt products include the Colt Walker, made 1847 in the facilities of Eli Whitney Jr. Though they did not develop it, for a long time Colt was also responsible for all AR-15 and M16 rifle production. The most successful and famous of these are numerous M16 carbines, including the Colt Commando family, in 2002, Colt Defense was split off from Colts Manufacturing Company. Colts Manufacturing Company now serves the market, while Colt Defense serves the law enforcement, military. The two companies remained in the same West Hartford, Connecticut location cross-licensing certain merchandise before reuniting in 2013, following the loss of its M4 contract in 2013, Colt was briefly in Chapter 11 Bankruptcy, starting in 2015. Samuel Colt received a British patent on his design for a revolver in 1835. That same year, he founded his first corporation for its manufacture, the first firearm manufactured at the new Paterson plant, however, was the Colt First Model Ring Lever rifle beginning in 1837. This was followed thereafter in late 1837 by the introduction of the Colt Paterson. This corporation suffered quality problems in production, making firearms with interchangeable parts was still rather new, and it was not yet easy to replicate across different factories. Interchangeability was not complete in the Paterson works, and traditional gunsmithing techniques did not fill the gap entirely there, the Colt Paterson revolver found patchy success and failure, some worked well, while others had problems. The United States Marine Corps and United States Army reported quality problems with these earliest Colt revolvers, production had ended at the New Jersey corporation by 1842. Colt made another attempt at revolver production in 1846 and submitted a prototype to the US government, during the Mexican–American War, this prototype was seen by Captain Samuel Hamilton Walker who made some suggestions to Colt about making it in a larger caliber. Having no factory or machinery to produce the pistols, Samuel Colt collaborated with the Whitney armory of Whitneyville and this armory was run by the family of Eli Whitney. Eli Whitney Jr, the son of the patriarch, was the head of the family armory
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