1.
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
2.
Helmholtz coil
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A Helmholtz coil is a device for producing a region of nearly uniform magnetic field, named after the German physicist Hermann von Helmholtz. It consists of two solenoid electromagnets on the same axis, besides creating magnetic fields, Helmholtz coils are also used in scientific apparatus to cancel external magnetic fields, such as the Earths magnetic field. Each coil carries an electric current in the same direction. In some applications, a Helmholtz coil is used to out the Earths magnetic field. The calculation of the magnetic field at any point in space is mathematically complex. By symmetry, the terms in the expansion are zero. The inflection point for a coil is located along the coil axis at a distance R /2 from its centre. Thus the locations for the two coils are x = ± R /2, the calculation detailed below gives the exact value of the magnetic field at the center point. Start with the formula for the field due to a single wire loop. The Helmholtz coils consists of n turns of wire, so the equivalent current in a coil is n times the current I in the n-turn coil. Substituting nI for I in the formula gives the field for an n-turn coil. In a Helmholtz coil, a point halfway between the two loops has an x value equal to R/2, so calculate the strength at that point. There are also two coils instead of one, most Helmholtz coils use DC current to produce a static magnetic field. Many applications and experiments require a time-varying magnetic field and these applications include magnetic field susceptibility tests, scientific experiments, and biomedical studies. The required magnetic fields are usually either pulse or continuous sinewave, the magnetic field frequency range can be anywhere from near DC to many kilohertz or even megahertz. An AC Helmholtz coil driver is needed to generate the required time-varying magnetic field, the waveform amplifier driver must be able to output high AC current to produce the magnetic field. Use the above equation in the section to calculate the coil current for a desired magnetic field. Generating a static field is relatively easy, the strength of the field is proportional to the current
3.
Fluorescence
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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. Fluorescent materials cease to glow immediately when the radiation source stops, unlike phosphorescence, Fluorescence also occurs frequently in nature in some minerals and in various biological states in many branches of the animal kingdom. An early observation of fluorescence was described in 1560 by Bernardino de Sahagún and it was derived from the wood of two tree species, Pterocarpus indicus and Eysenhardtia polystachya. The chemical compound responsible for this fluorescence is matlaline, which is the product of one of the flavonoids found in this wood. The name was derived from the fluorite, some examples of which contain traces of divalent europium. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight, the specific frequencies of exciting and emitted light are dependent on the particular system. S0 is called the state of the fluorophore, and S1 is its first excited singlet state. A molecule in S1 can relax by various competing pathways and it can undergo non-radiative relaxation in which the excitation energy is dissipated as heat to the solvent. Excited organic molecules can also relax via conversion to a triplet state, relaxation from S1 can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation, this phenomenon is known as the Stokes shift. The emitted radiation may also be of the wavelength as the absorbed radiation. Molecules that are excited through light absorption or via a different process can transfer energy to a second sensitized molecule, the fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed, Φ = Number of photons emitted Number of photons absorbed The maximum fluorescence quantum yield is 1.0, each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent, thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected. Fluorescence quantum yields are measured by comparison to a standard, the quinine salt quinine sulfate in a sulfuric acid solution is a common fluorescence standard. The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. This is an instance of exponential decay, various radiative and non-radiative processes can de-populate the excited state
4.
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
5.
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
6.
Electrode
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An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. The word was coined by William Whewell at the request of the scientist Michael Faraday from the Greek words elektron, meaning amber, and hodos, an electrode in an electrochemical cell is referred to as either an anode or a cathode. The anode is now defined as the electrode at which electrons leave the cell and oxidation occurs, each electrode may become either the anode or the cathode depending on the direction of current through the cell. A bipolar electrode is an electrode that functions as the anode of one cell, a primary cell is a special type of electrochemical cell in which the reaction cannot be reversed, and the identities of the anode and cathode are therefore fixed. The anode is always the negative electrode, the cell can be discharged but not recharged. A secondary cell, for example a rechargeable battery, is a cell in which the reactions are reversible. When the cell is being charged, the anode becomes the positive and this is also the case in an electrolytic cell. When the cell is being discharged, it behaves like a cell, with the anode as the negative. In a vacuum tube or a semiconductor having polarity the anode is the positive electrode, the electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e. g. base, gate, control grid. In a three-electrode cell, an electrode, also called an auxiliary electrode, is used only to make a connection to the electrolyte so that a current can be applied to the working electrode. The counter electrode is made of an inert material, such as a noble metal or graphite. In arc welding an electrode is used to conduct current through a workpiece to fuse two pieces together. Depending upon the process, the electrode is either consumable, in the case of gas metal arc welding or shielded metal arc welding, or non-consumable, such as in gas tungsten arc welding. For a direct current system the weld rod or stick may be a cathode for a filling type weld or an anode for other welding processes, for an alternating current arc welder the welding electrode would not be considered an anode or cathode. Electrodes are used to provide current through nonmetal objects to them in numerous ways. These electrodes are used for advanced purposes in research and investigation
7.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
8.
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
9.
Johann Wilhelm Hittorf
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Johann Wilhelm Hittorf was a German physicist who was born in Bonn and died in Münster, Germany. Hittorf was the first to compute the electricity-carrying capacity of charged atoms and molecules and he formulated ion transport numbers and the first method for their measurements. He observed tubes with energy rays extending from a negative electrode and these rays produced a fluorescence when they hit the glass walls of the tubes. In 1876 the effect was named cathode rays by Eugen Goldstein, hittorfs early investigations were on the allotropes of phosphorus and selenium. Between 1853 and 1859 his most important work was on ion movement caused by electric current, in 1853 Hittorf pointed out that some ions traveled more rapidly than others. This observation led to the concept of number, the fraction of the electric current carried by each ionic species. He measured the changes in the concentration of electrolyzed solutions, computed from these the numbers of many ions. He became professor of physics and chemistry at the University of Münster and he also investigated the light spectra of gases and vapours, worked on the passage of electricity through gases, and discovered new properties of cathode rays. In 1869 he ascertained that the cathode rays glowed different colours because of different gasses and pressures and he noticed that when there was any object placed between the cathode and the illuminating side of the tube, then the shadow of that object appeared. His work led toward development of X-rays and cathode ray tubes, the measurement of current in a vacuum tube was an important step towards the creation of a vacuum tube diode. Biographical sketch and reprint of paper on migration of ions The Cathode Ray Tube site
10.
J. J. Thomson
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He was elected as a fellow of the Royal Society of London and appointed to the Cavendish Professorship of Experimental Physics at the Cambridge Universitys Cavendish Laboratory in 1884. Thomson is also credited with finding the first evidence for isotopes of an element in 1913. His experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry, Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases. Seven of his students, including his son George Paget Thomson and his record is comparable only to that of the German physicist Arnold Sommerfeld. Joseph John Thomson was born 18 December 1856 in Cheetham Hill, Manchester, Lancashire and his mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran a bookshop founded by a great-grandfather. He had a two years younger than he was, Frederick Vernon Thomson. J. J. Thomson was a devout Anglican and his early education was in small private schools where he demonstrated outstanding talent and interest in science. In 1870 he was admitted to Owens College at the young age of 14. His parents planned to enroll him as an engineer to Sharp-Stewart & Co, a locomotive manufacturer. He moved on to Trinity College, Cambridge, in 1876, in 1880 he obtained his BA in mathematics. He applied for and became a Fellow of Trinity College in 1881, Thomson received his MA in 1883. Thomson was elected a Fellow of the Royal Society on 12 June 1884, on 22 December 1884 Thomson was chosen to become Cavendish Professor of Physics at the University of Cambridge. The appointment caused considerable surprise, given that such as Richard Glazebrook were older. Thomson was known for his work as a mathematician, where he was recognized as an exceptional talent. In 1890, Thomson married Rose Elisabeth Paget, daughter of Sir George Edward Paget, KCB and they had one son, George Paget Thomson, and one daughter, Joan Paget Thomson. He was awarded a Nobel Prize in 1906, in recognition of the merits of his theoretical and experimental investigations on the conduction of electricity by gases. He was knighted in 1908 and appointed to the Order of Merit in 1912, in 1914 he gave the Romanes Lecture in Oxford on The atomic theory
11.
Cathode ray tube
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The cathode ray tube is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images. It modulates, accelerates, and deflects electron beam onto the screen to create the images, the images may represent electrical waveforms, pictures, radar targets, or others. CRTs have also used as memory devices, in which case the visible light emitted from the fluorescent material is not intended to have significant meaning to a visual observer. In television sets and computer monitors, the front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. An image is produced by controlling the intensity of each of the three beams, one for each additive primary color with a video signal as a reference. A CRT is constructed from an envelope which is large, deep, fairly heavy. The interior of a CRT is evacuated to approximately 0.01 Pa to 133 nPa. evacuation being necessary to facilitate the flight of electrons from the gun to the tubes face. That it is evacuated makes handling an intact CRT potentially dangerous due to the risk of breaking the tube and causing a violent implosion that can hurl shards of glass at great velocity. As a matter of safety, the face is made of thick lead glass so as to be highly shatter-resistant and to block most X-ray emissions. Flat panel displays can also be made in large sizes, whereas 38 to 40 was about the largest size of a CRT television, flat panels are available in 60. Cathode rays were discovered by Johann Hittorf in 1869 in primitive Crookes tubes and he observed that some unknown rays were emitted from the cathode which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, the earliest version of the CRT was known as the Braun tube, invented by the German physicist Ferdinand Braun in 1897. It was a diode, a modification of the Crookes tube with a phosphor-coated screen. In 1907, Russian scientist Boris Rosing used a CRT in the end of an experimental video signal to form a picture. He managed to display simple geometric shapes onto the screen, which marked the first time that CRT technology was used for what is now known as television. The first cathode ray tube to use a hot cathode was developed by John B. Johnson and Harry Weiner Weinhart of Western Electric and it was named by inventor Vladimir K. Zworykin in 1929. RCA was granted a trademark for the term in 1932, it released the term to the public domain in 1950. The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934, in oscilloscope CRTs, electrostatic deflection is used, rather than the magnetic deflection commonly used with television and other large CRTs
12.
Atom
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An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms, Atoms are very small, typical sizes are around 100 picometers. Atoms are small enough that attempting to predict their behavior using classical physics - as if they were billiard balls, through the development of physics, atomic models have incorporated quantum principles to better explain and predict the behavior. Every atom is composed of a nucleus and one or more bound to the nucleus. The nucleus is made of one or more protons and typically a number of neutrons. Protons and neutrons are called nucleons, more than 99. 94% of an atoms mass is in the nucleus. The protons have an electric charge, the electrons have a negative electric charge. If the number of protons and electrons are equal, that atom is electrically neutral, if an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an ion. The electrons of an atom are attracted to the protons in a nucleus by this electromagnetic force. The number of protons in the nucleus defines to what chemical element the atom belongs, for example, the number of neutrons defines the isotope of the element. The number of influences the magnetic properties of an atom. Atoms can attach to one or more other atoms by chemical bonds to form compounds such as molecules. The ability of atoms to associate and dissociate is responsible for most of the changes observed in nature. The idea that matter is made up of units is a very old idea, appearing in many ancient cultures such as Greece. The word atom was coined by ancient Greek philosophers, however, these ideas were founded in philosophical and theological reasoning rather than evidence and experimentation. As a result, their views on what look like. They also could not convince everybody, so atomism was but one of a number of competing theories on the nature of matter. It was not until the 19th century that the idea was embraced and refined by scientists, in the early 1800s, John Dalton used the concept of atoms to explain why elements always react in ratios of small whole numbers
13.
Cold cathode
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A cold cathode is a cathode that is not electrically heated by a filament. A cathode may be considered if it emits more electrons than can be supplied by thermionic emission alone. It is used in lamps, such as neon lamps, discharge tubes. The other type of cathode is a hot cathode, which is heated by current passing through a filament. A cold cathode does not necessarily operate at a low temperature, it is heated to its operating temperature by other methods. A cold-cathode vacuum tube does not rely on external heating of an electrode to provide thermionic emission of electrons, early cold-cathode devices included the Geissler tube and Plucker tube, and early cathode ray tubes. Study of the phenomena in these devices led to the discovery of the electron, neon lamps are used both to produce light as indicators and for special-purpose illumination, and also as circuit elements displaying negative resistance. Addition of an electrode to a device allowed the glow discharge to be initiated by an external control circuit. Many types of cold-cathode switching tube were developed, including types of thyratron. Voltage regulator tubes rely on the constant voltage of a glow discharge over a range of current. A Dekatron is a tube with multiple electrodes that is used for counting. Counter tubes were used widely before development of integrated circuit counter devices, the flash tube is a cold-cathode device filled with xenon gas, used to produce an intense short pulse of light for photography or to act as a stroboscope to examine the motion of moving parts. Cold-cathode lamps include cold-cathode fluorescent lamps and neon lamps, cold-cathode fluorescent lamps are used for backlighting of LCDs, for example computer monitors and television screens. In the lighting industry, “cold cathode” historically refers to luminous tubing which is larger than 20mm in diameter and this larger diameter tubing is often used for interior alcove and general lighting. The term neon lamp refers to tubing that is smaller than 15 mm diameter and these lamps are commonly used for neon signs. The cathode is the negative electrode, any gas discharge lamp has a positive and a negative electrode. Both electrodes alternate between acting as an anode and a cathode when these devices run with alternating current, a cold cathode is distinguished from a hot cathode that is heated to induce thermionic emission of electrons. Discharge tubes with hot cathodes have an envelope filled with low pressure gas, examples are most common fluorescent lamps, high pressure discharge lamps and vacuum fluorescent displays
14.
Crookes tube
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Developed from the earlier Geissler tube, the Crookes tube consists of a partially evacuated glass bulb of various shapes, with two metal electrodes, the cathode and the anode, one at either end. When a high voltage is applied between the electrodes, cathode rays are projected in straight lines from the cathode. It was used by Crookes, Johann Hittorf, Julius Plücker, Eugen Goldstein, Heinrich Hertz, Philipp Lenard and others to discover the properties of cathode rays, thomsons 1897 identification of cathode rays as negatively charged particles, which were later named electrons. Crookes tubes are now used only for demonstrating cathode rays, Wilhelm Röntgen discovered X-rays using the Crookes tube in 1895. The term Crookes tube is used for the first generation, cold cathode X-ray tubes. Crookes tubes are cold cathode tubes, meaning that they do not have a filament in them that releases electrons as the later electronic vacuum tubes usually do. Instead, electrons are generated by the ionization of the air by a high DC voltage applied between the electrodes, usually by an induction coil. The Crookes tubes require an amount of air in them to function. The electrons collide with gas molecules, knocking electrons off them. All the positive ions are attracted to the cathode or negative electrode, when they strike it, they knock large numbers of electrons out of the surface of the metal, which in turn are repelled by the cathode and attracted to the anode or positive electrode. Enough of the air has been removed from the tube that most of the electrons can travel the length of the tube without striking a gas molecule, the high voltage accelerates these low-mass particles to a high velocity. When they get to the end of the tube, they have so much momentum that, although they are attracted to the anode, many fly past it. When they strike atoms in the glass, they knock their orbital electrons into an energy level. When the electrons back to their original energy level, they emit light. This process, called fluorescence, causes the glass to glow, the electrons themselves are invisible, but the glow reveals where the beam of electrons strikes the glass. Later on, researchers painted the back wall of the tube with a phosphor. After striking the wall, the electrons eventually make their way to the anode, flow through the wire, the power supply. The above only describes the motion of the electrons, at higher gas pressures, above 10−6 atm, this creates a glow discharge, a pattern of different colored glowing regions in the gas, depending on the pressure in the tube
15.
Ionization
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Ionization is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons to form ions, often in conjunction with other chemical changes. Ionization can result from the loss of an electron after collisions with particles, collisions with other atoms, molecules and ions. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs, ionization can occur through radioactive decay by the internal conversion process, in which an excited nucleus transfers its energy to one of the inner-shell electrons causing it to be ejected. Everyday examples of gas ionization are such as within a fluorescent lamp or other electrical discharge lamps and it is also used in radiation detectors such as the Geiger-Müller counter or the ionization chamber. The ionization process is used in a variety of equipment in fundamental science and in such as mass spectrometry. Negatively charged ions are produced when an electron collides with an atom and is subsequently trapped inside the electric potential barrier. The process is known as electron capture ionization, positively charged ions are produced by transferring a sufficient amount of energy to a bound electron in a collision with charged particles or with photons. The threshold amount of the energy is known as ionization potential. The study of such collisions is of importance with regard to the few-body problem. The Townsend discharge is an example of the creation of positive ions. It is a reaction involving electrons in a region with a sufficiently high electric field in a gaseous medium that can be ionized. Following an original event, due to such as ionizing radiation. If the electric field is strong enough, the free electron gains sufficient energy to liberate a further electron when it collides with another molecule. The two free electrons then travel towards the anode and gain sufficient energy from the field to cause impact ionization when the next collisions occur. This is effectively a chain reaction of electron generation, and is dependent on the free electrons gaining sufficient energy between collisions to sustain the avalanche, ionization efficiency is the ratio of the number of ions formed to the number of electrons or photons used. The trend in the energy of atoms is often used to demonstrate the periodic behavior of atoms with respect to the atomic number. This is a tool for establishing and understanding the ordering of electrons in atomic orbitals without going into the details of wave functions or the ionization process. An example is presented in figure 1, the periodic abrupt decrease in ionization potential after rare gas atoms, for instance, indicates the emergence of a new shell in alkali metals
16.
Thermionic emission
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Thermionic emission is the thermally induced flow of charge carriers from a surface or over a potential-energy barrier. This occurs because the energy given to the carrier overcomes the work function of the material. The charge carriers can be electrons or ions, and in literature are sometimes referred to as thermions. After emission, a charge that is equal in magnitude and opposite in sign to the total charge emitted is initially left behind in the emitting region, the classical example of thermionic emission is the emission of electrons from a hot cathode into a vacuum in a vacuum tube. The hot cathode can be a metal filament, a metal filament. Vacuum emission from metals tends to become significant only for temperatures over 1,000 K, the term thermionic emission is now also used to refer to any thermally-excited charge emission process, even when the charge is emitted from one solid-state region into another. This process is important in the operation of a variety of electronic devices. The magnitude of the flow increases dramatically with increasing temperature. The phenomenon was reported in 1853 by Edmond Becquerel. It was rediscovered in 1873 by Frederick Guthrie in Britain, while doing work on charged objects, Guthrie discovered that a red-hot iron sphere with a negative charge would lose its charge. He also found that this did not happen if the sphere had a positive charge, other early contributors included Johann Wilhelm Hittorf, Eugen Goldstein, and Julius Elster and Hans Friedrich Geitel. Edison built several experimental lamp bulbs with a wire, metal plate, or foil inside the bulb that was separate from the filament. He connected a galvanometer, a used to measure current. If the foil was put at a negative potential relative to the filament and we now know that the filament was emitting electrons, which were attracted to a positively charged foil, but not a negatively charged one. This one-way current was called the Edison effect and he found that the current emitted by the hot filament increased rapidly with increasing voltage, and filed a patent application for a voltage-regulating device using the effect on November 15,1883. He found that sufficient current would pass through the device to operate a telegraph sounder and this was exhibited at the International Electrical Exposition in Philadelphia in September 1884. William Preece, a British scientist, took back with him several of the Edison effect bulbs and he presented a paper on them in 1885, where he referred to thermionic emission as the Edison Effect. The British physicist John Ambrose Fleming, working for the British Wireless Telegraphy Company, Fleming went on to develop the two-element vacuum tube known as the diode, which he patented on November 16,1904
17.
Electrical filament
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An incandescent light bulb, incandescent lamp or incandescent light globe is an electric light with a wire filament heated to such a high temperature that it glows with visible light. The filament, heated by passing a current through it, is protected from oxidation with a glass or quartz bulb that is filled with inert gas or evacuated. In a halogen lamp, filament evaporation is prevented by a process that redeposits metal vapor onto the filament. The light bulb is supplied with current by feed-through terminals or wires embedded in the glass. Most bulbs are used in a socket which provides mechanical support, Incandescent bulbs are manufactured in a wide range of sizes, light output, and voltage ratings, from 1.5 volts to about 300 volts. They require no external regulating equipment, have low manufacturing costs, the remaining energy is converted into heat. The luminous efficacy of an incandescent bulb is 16 lumens per watt. Some applications of the incandescent bulb deliberately use the heat generated by the filament, such applications include incubators, brooding boxes for poultry, heat lights for reptile tanks, infrared heating for industrial heating and drying processes, lava lamps, and the Easy-Bake Oven toy. In addressing the question of who invented the incandescent lamp, historians Robert Friedel and Paul Israel list 22 inventors of incandescent lamps prior to Joseph Swan, historian Thomas Hughes has attributed Edisons success to his development of an entire, integrated system of electric lighting. In 1761 Ebenezer Kinnersley demonstrated heating a wire to incandescence and it was not bright enough nor did it last long enough to be practical, but it was the precedent behind the efforts of scores of experimenters over the next 75 years. Over the first three-quarters of the 19th century many experimenters worked with various combinations of platinum or iridium wires, carbon rods, many of these devices were demonstrated and some were patented. In 1835, James Bowman Lindsay demonstrated a constant electric light at a meeting in Dundee. He stated that he could read a book at a distance of one, however, having perfected the device to his own satisfaction, he turned to the problem of wireless telegraphy and did not develop the electric light any further. His claims are not well documented, although he is credited in Challoner et al. with being the inventor of the Incandescent Light Bulb, in 1838, Belgian lithographer Marcellin Jobard invented an incandescent light bulb with a vacuum atmosphere using a carbon filament. In 1840, British scientist Warren de la Rue enclosed a coiled platinum filament in a vacuum tube, although a workable design, the cost of the platinum made it impractical for commercial use. In 1841, Frederick de Moleyns of England was granted the first patent for an incandescent lamp, in 1845, American John W. Starr acquired a patent for his incandescent light bulb involving the use of carbon filaments. He died shortly after obtaining the patent, and his invention was never produced commercially, little else is known about him. In 1851, Jean Eugène Robert-Houdin publicly demonstrated incandescent light bulbs on his estate in Blois and his light bulbs are on display in the museum of the Château de Blois
18.
Electric current
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An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarily
19.
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
20.
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
21.
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
22.
Transmitter
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In electronics and telecommunications a transmitter or radio transmitter is an electronic device which generates a radio frequency alternating current. When a connected antenna is excited by this current, the antenna emits radio waves. The term transmitter is usually limited to equipment that generates radio waves for communication purposes, or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits. The term is used more specifically to refer to a broadcast transmitter. This usage typically includes both the proper, the antenna, and often the building it is housed in. A transmitter can be a piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and a receiver combined in one unit is called a transceiver, the term transmitter is often abbreviated XMTR or TX in technical documents. The purpose of most transmitters is radio communication of information over a distance, the transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is called the carrier signal. The information can be added to the carrier in several different ways, in an amplitude modulation transmitter, the information is added to the radio signal by varying its amplitude. In a frequency modulation transmitter, it is added by varying the signals frequency slightly. Many other types of modulation are used, the radio signal from the transmitter is applied to the antenna, which radiates the energy as radio waves. The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as phones, walkie-talkies. In more powerful transmitters, the antenna may be located on top of a building or on a tower, and connected to the transmitter by a feed line. The first primitive radio transmitters were built by German physicist Heinrich Hertz in 1887 during his investigations of radio waves. These generated radio waves by a high voltage spark between two conductors, beginning in 1895 Guglielmo Marconi developed the first practical radio communication systems using spark transmitters. These spark-gap transmitters were used during the first three decades of radio, called the wireless telegraphy or spark era, vacuum tube transmitters took over because they were inexpensive and produced continuous waves, which could be modulated to transmit audio using amplitude modulation. This made possible commercial AM radio broadcasting, which began in about 1920, experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didnt begin until the 1940s
23.
Electric field
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An electric field is a vector field that associates to each point in space the Coulomb force that would be experienced per unit of electric charge, by an infinitesimal test charge at that point. Electric fields are created by electric charges and can be induced by time-varying magnetic fields, the electric field combines with the magnetic field to form the electromagnetic field. The electric field, E, at a point is defined as the force, F. A particle of charge q would be subject to a force F = q E and its SI units are newtons per coulomb or, equivalently, volts per metre, which in terms of SI base units are kg⋅m⋅s−3⋅A−1. Electric fields are caused by electric charges or varying magnetic fields, in the special case of a steady state, the Maxwell-Faraday inductive effect disappears. The resulting two equations, taken together, are equivalent to Coulombs law, written as E =14 π ε0 ∫ d r ′ ρ r − r ′ | r − r ′ |3 for a charge density ρ. Notice that ε0, the permittivity of vacuum, must be substituted if charges are considered in non-empty media, the equations of electromagnetism are best described in a continuous description. A charge q located at r 0 can be described mathematically as a charge density ρ = q δ, conversely, a charge distribution can be approximated by many small point charges. Electric fields satisfy the principle, because Maxwells equations are linear. This principle is useful to calculate the field created by point charges. Q n are stationary in space at r 1, r 2, in that case, Coulombs law fully describes the field. If a system is static, such that magnetic fields are not time-varying, then by Faradays law, in this case, one can define an electric potential, that is, a function Φ such that E = − ∇ Φ. This is analogous to the gravitational potential, Coulombs law, which describes the interaction of electric charges, F = q = q E is similar to Newtons law of universal gravitation, F = m = m g. This suggests similarities between the electric field E and the gravitational field g, or their associated potentials, mass is sometimes called gravitational charge because of that similarity. Electrostatic and gravitational forces both are central, conservative and obey an inverse-square law, a uniform field is one in which the electric field is constant at every point. It can be approximated by placing two conducting plates parallel to other and maintaining a voltage between them, it is only an approximation because of boundary effects. Assuming infinite planes, the magnitude of the electric field E is, electrodynamic fields are E-fields which do change with time, for instance when charges are in motion. The electric field cannot be described independently of the field in that case
24.
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
25.
Electron microscope
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An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. Transmission electron microscopes use electrostatic and electromagnetic lenses to control the electron beam and these electron optical lenses are analogous to the glass lenses of an optical light microscope. Industrially, electron microscopes are used for quality control and failure analysis. Modern electron microscopes produce electron micrographs using specialized digital cameras and frame grabbers to capture the image, the first electromagnetic lens was developed in 1926 by Hans Busch. According to Dennis Gabor, the physicist Leó Szilárd tried in 1928 to convince Busch to build an electron microscope, two years later, in 1933, Ruska built an electron microscope that exceeded the resolution attainable with an optical microscope. Moreover, Reinhold Rudenberg, the director of Siemens-Schuckertwerke, obtained the patent for the electron microscope in May 1931. In 1932, Ernst Lubcke of Siemens & Halske built and obtained images from an electron microscope. Five years later, the firm financed the work of Ernst Ruska and Bodo von Borries, also in 1937, Manfred von Ardenne pioneered the scanning electron microscope. The first commercial electron microscope was produced in 1938 by Siemens, although contemporary transmission electron microscopes are capable of two million-power magnification, as scientific instruments, they remain based upon Ruska’s prototype. The original form of electron microscope, the electron microscope uses a high voltage electron beam to illuminate the specimen. The electron beam is produced by a gun, commonly fitted with a tungsten filament cathode as the electron source. When it emerges from the specimen, the electron beam carries information about the structure of the specimen that is magnified by the lens system of the microscope. The image detected by the camera may be displayed on a monitor or computer. The resolution of TEMs is limited primarily by spherical aberration, but a new generation of aberration correctors have been able to partially overcome spherical aberration to increase resolution. The ability to determine the positions of atoms within materials has made the HRTEM an important tool for nano-technologies research, transmission electron microscopes are often used in electron diffraction mode. The major disadvantage of the electron microscope is the need for extremely thin sections of the specimens. Biological specimens are required to be chemically fixed, dehydrated and embedded in a polymer resin to stabilize them sufficiently to allow ultrathin sectioning. Sections of biological specimens, organic polymers and similar materials may require treatment with heavy atom labels in order to achieve the required image contrast
26.
Vacuum pump
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A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke, and was preceded by the suction pump, the predecessor to the vacuum pump was the suction pump, which was known to the Romans. Dual-action suction pumps were found in the city of Pompeii, arabic engineer Al-Jazari also described suction pumps in the 13th century. He said that his model was a version of the siphons the Byzantines used to discharge the Greek fire. The suction pump later reappeared in Europe from the 15th century, by the 17th century, water pump designs had improved to the point that they produced measurable vacuums, but this was not immediately understood. What was known was that suction pumps could not pull water beyond a certain height,18 Florentine yards according to a measurement taken around 1635. This limit was a concern to irrigation projects, mine drainage, Galileo advertised the puzzle to other scientists, including Gaspar Berti who replicated it by building the first water barometer in Rome in 1639. Bertis barometer produced a vacuum above the column, but he could not explain it. The breakthrough was made by Evangelista Torricelli in 1643, building upon Galileos notes, he built the first mercury barometer and wrote a convincing argument that the space at the top was a vacuum. Robert Boyle improved Guerickes design and conducted experiments on the properties of vacuum, robert Hooke also helped Boyle produce an air pump which helped to produce the vacuum. The study of vacuum then lapsed until 1855, when Heinrich Geissler invented the mercury displacement pump, a number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. This, in turn, led to the development of the vacuum tube, in the 19th century, Nikola Tesla designed an apparatus that contains a Sprengel pump to create a high degree of exhaustion. Momentum transfer pumps, also called molecular pumps, use high speed jets of dense fluid or high speed rotating blades to knock gas molecules out of the chamber, entrapment pumps capture gases in a solid or adsorbed state. This includes cryopumps, getters, and ion pumps, positive displacement pumps are the most effective for low vacuums. Momentum transfer pumps in conjunction with one or two positive displacement pumps are the most common used to achieve high vacuums. In this configuration the positive displacement pump serves two purposes, second the positive displacement pump backs up the momentum transfer pump by evacuating to low vacuum the accumulation of displaced molecules in the high vacuum pump. Entrapment pumps can be added to reach ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules or ions, due to this requirement their available operational time can be unacceptably short in low and high vacuums, thus limiting their use to ultrahigh vacuums. A partial vacuum may be generated by increasing the volume of a container, to continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again
27.
Otto von Guericke
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Otto von Guericke was a German scientist, inventor, and politician. Otto von Guericke was born to a family of Magdeburg. In 1617 he became a student at the Leipzig University, owing to the outbreak of the Thirty Years War his studies at Leipzig were disrupted and subsequently he studied at the Academia Julia in Helmstedt and the universities of Jena and Leyden. At the last of these he attended courses on mathematics, physics and his education was completed by a nine-month-long trip to France and England. On his return to Magdeburg in 1626 he married Margarethe Alemann and he was to remain a member of this body until old age. Von Guericke was personally distrustful of the enthusiasm for the cause of Gustavus Adolphus but was nonetheless a victim of the fall of Magdeburg to von Tillys troops in May 1631. Following a period of employment as engineer in the service of Gustavus Adolphus he, for the next decade he was occupied rebuilding his own and the citys fortunes from the ruins of the fire of 1631. Diplomatic missions, often dangerous as well as tedious, occupied much of his time for the twenty years. A private scientific life, of which remains unclear, was developing in parallel. One of them, the Archbishop Elector Johann Philip von Schonborn, one of the professors at the College, Fr. Gaspar Schott, entered into correspondence with von Guericke and thus it was that, at the age of 55. Schott - Mechanica Hydraulico-pneumatica - published in 1657, the following year this was translated into Latin and, made aware of it in correspondence with Fr. Schott, von Guericke acquired a copy, in the decade following the first publication of his own work von Guericke, in addition to his diplomatic and administrative commitments, was scientifically very active. In the Preface to the Reader he claims to have finished the book on March 14,1663 though publication was delayed for nine years until 1672. In 1664, his work appeared in print, again through the good offices of Fr. Schott, the first section of whose book Technica Curiosa, entitled Mirabilia Magdeburgica, was dedicated to von Guerickes work, the earliest reference to the celebrated Magdeburg hemispheres experiment is on p.39 of the Technica Curiosa, where Fr. Schott notes that von Guericke had mentioned them in a letter of July 22,1656. Schott goes on to quote a subsequent letter of von Guericke of August 4,1657 in which he states that he now had carried out the experiment, at considerable cost, with 12 horses
28.
Electrostatic generator
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An electrostatic generator, or electrostatic machine, is an electromechanical generator that produces static electricity, or electricity at high voltage and low continuous current. Electrostatic generators operate by using manual power to mechanical work into electric energy. The charge is generated by one of two methods, either the effect or electrostatic induction. Electrostatic machines are used in science classrooms to safely demonstrate electrical forces. Electrostatic generators such as the Van de Graaff generator, and variations as the Pelletron, a primitive form of frictional machine was invented around 1663 by Otto von Guericke, using a sulphur globe that could be rotated and rubbed by hand. It may not actually have been rotated during use and was not intended to produce electricity, isaac Newton suggested the use of a glass globe instead of a sulphur one. Francis Hauksbee improved the design, with his frictional electrical machine that enabled a glass sphere to be rotated rapidly against a woollen cloth. Generators were further advanced when Prof. Georg Matthias Bose of Wittenberg added a collecting conductor. Bose was the first to employ the prime conductor in such machines, in 1746, William Watsons machine had a large wheel turning several glass globes, with a sword and a gun barrel suspended from silk cords for its prime conductors. Johann Heinrich Winckler, professor of physics at Leipzig, substituted a leather cushion for the hand, during 1746, Jan Ingenhousz invented electric machines made of plate glass. In 1768, Jesse Ramsden constructed a widely used version of an electrical generator. In 1783, Dutch scientist Martin van Marum of Haarlem designed a large electrostatic machine of high quality with glass disks 1.65 meters in diameter for his experiments. Capable of producing voltage with either polarity, it was built under his supervision by John Cuthbertson of Amsterdam the following year, the generator is currently on display at the Teylers Museum in Haarlem. In 1785, N. Rouland constructed a machine that rubbed two grounded tubes covered with hare fur. The Winter machine possessed higher efficiency than earlier friction machines, in the 1830s, Georg Ohm possessed a machine similar to the Van Marum machine for his research. In 1840, the Woodward machine was developed by improving the Ramsden machine, also in 1840, the Armstrong hydroelectric machine was developed, using steam as a charge carrier. The presence of charge imbalance means that the objects will exhibit attractive or repulsive forces. Rubbing two non-conductive objects generates a great amount of static electricity and this is not the result of friction, two non-conductive surfaces can become charged by just being placed one on top of the other
29.
Glow discharge
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A glow discharge is a plasma formed by the passage of electric current through a low-pressure gas. It is created by applying a voltage between two electrodes in a glass tube containing gas. When the voltage exceeds a value called the striking voltage, the gas in the tube ionizes, becoming a plasma. The color depends on the gas used, glow discharge is widely used as a source of light in devices such as neon lights, fluorescent lamps, and plasma-screen televisions. Analyzing the light produced by spectroscopy can reveal much about the interactions in the gas, so glow discharge is used in plasma physics. It is also used in the surface treatment technique called sputtering, the simplest type of glow discharge is a direct-current glow discharge. In its simplest form, it consists of two electrodes in a cell held at low pressure, the cell is typically filled with neon, but other gases can also be used. An electric potential of several hundred volts is applied between the two electrodes, a small fraction of the population of atoms within the cell is initially ionized through random processes. The ions are driven towards the cathode by the potential. The initial population of ions and electrons collides with other atoms, as long as the potential is maintained, a population of ions and electrons remains. Some of the kinetic energy is transferred to the cathode. This happens partially through the ions striking the cathode directly, the primary mechanism, however, is less direct. Ions strike the more numerous neutral gas atoms, transferring a portion of their energy to them and these neutral atoms then strike the cathode. Whichever species strike the cathode, collisions within the cathode redistribute this energy until a portion of the cathode is ejected and this process is known as sputtering. Once free of the cathode, atoms move into the bulk of the discharge through drift. The atoms can then be excited by collisions with ions, electrons, once excited, atoms will lose their energy fairly quickly. Of the various ways that this energy can be lost, the most important is radiatively, in atomic mass spectrometry, these ions are detected. Their mass identifies the type of atoms and their quantity reveals the amount of element in the sample
30.
Michael Faraday
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Michael Faraday FRS was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic induction, diamagnetism, although Faraday received little formal education, he was one of the most influential scientists in history. It was by his research on the field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was a relationship between the two phenomena. He similarly discovered the principles of induction and diamagnetism. His inventions of electromagnetic rotary devices formed the foundation of electric motor technology, Faraday ultimately became the first and foremost Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a lifetime position. James Clerk Maxwell took the work of Faraday and others and summarized it in a set of equations which is accepted as the basis of all theories of electromagnetic phenomena. The SI unit of capacitance is named in his honour, the farad, albert Einstein kept a picture of Faraday on his study wall, alongside pictures of Isaac Newton and James Clerk Maxwell. Faraday was born in Newington Butts, which is now part of the London Borough of Southwark but was then a part of Surrey. His family was not well off and his father, James, was a member of the Glassite sect of Christianity. James Faraday moved his wife and two children to London during the winter of 1790 from Outhgill in Westmorland, where he had been an apprentice to the village blacksmith, Michael was born in the autumn of that year. The young Michael Faraday, who was the third of four children, at the age of 14 he became an apprentice to George Riebau, a local bookbinder and bookseller in Blandford Street. During his seven-year apprenticeship Faraday read many books, including Isaac Wattss The Improvement of the Mind, at this time he also developed an interest in science, especially in electricity. Faraday was particularly inspired by the book Conversations on Chemistry by Jane Marcet, many of the tickets for these lectures were given to Faraday by William Dance, who was one of the founders of the Royal Philharmonic Society. Faraday subsequently sent Davy a 300-page book based on notes that he had taken during these lectures, davys reply was immediate, kind, and favourable. In 1813, when Davy damaged his eyesight in an accident with nitrogen trichloride, very soon Davy entrusted Faraday with the preparation of nitrogen trichloride samples, and they both were injured in an explosion of this very sensitive substance. In the class-based English society of the time, Faraday was not considered a gentleman, Faraday was forced to fill the role of valet as well as assistant throughout the trip. Davys wife, Jane Apreece, refused to treat Faraday as an equal, the trip did, however, give him access to the scientific elite of Europe and exposed him to a host of stimulating ideas
31.
Induction coil
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An induction coil or spark coil is a type of electrical transformer used to produce high-voltage pulses from a low-voltage direct current supply. To create the changes necessary to induce voltage in the secondary coil. Invented in 1836 by Nicholas Callan, Charles Page and others and it was widely used in x-ray machines, spark-gap radio transmitters, arc lighting and quack medical electrotherapy devices from the 1880s to the 1920s. Today its only use is as the ignition coils in internal combustion engines. An induction coil consists of two coils of insulated wire wound around a common iron core. One coil, called the winding, is made from relatively few turns of coarse wire. The other coil, the winding, typically consists of many turns of fine wire. An electric current is passed through the primary, creating a magnetic field, because of the common core, most of the primarys magnetic field couples with the secondary winding. The primary behaves as an inductor, storing energy in the magnetic field. When the primary current is interrupted, the magnetic field rapidly collapses. This causes a voltage pulse to be developed across the secondary terminals through electromagnetic induction. Because of the number of turns in the secondary coil. This voltage is sufficient to cause an electric spark, to jump across an air gap separating the secondarys output terminals. For this reason, induction coils were called spark coils, the size of induction coils is usually specified by the length of spark it can produce, a 4 inch induction coil is one that could produce a 4 inch spark. This form of specification was, though imprecise, until the advent of the cathode ray oscilloscope the most reliable measure of voltage of such asymmetric waveforms. To do that, induction coils use a magnetically activated vibrating arm called an interrupter or break to rapidly connect, the interrupter is mounted on the end of the coil next to the iron core. When the power is turned on, the current in the primary coil produces an increasing magnetic field. After a time, the magnetic attraction overcomes the spring force
32.
Kilovolt
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The volt is the derived unit for electric potential, electric potential difference, and electromotive force. One volt is defined as the difference in potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can also be expressed as amperes times ohms, watts per ampere, or joules per coulomb, for the Josephson constant, KJ = 2e/h, the conventional value KJ-90 is used, K J-90 =0.4835979 GHz μ V. This standard is typically realized using an array of several thousand or tens of thousands of junctions. Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc. in the water-flow analogy sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping, the relationship between voltage and current is defined by Ohms Law. Ohms Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems, the voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. Cells can be combined in series for multiples of that voltage, mechanical generators can usually be constructed to any voltage in a range of feasibility. High-voltage electric power lines,110 kV and up Lightning, Varies greatly. Volta had determined that the most effective pair of metals to produce electricity was zinc. In 1861, Latimer Clark and Sir Charles Bright coined the name volt for the unit of resistance, by 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission and they made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. At that time, the volt was defined as the difference across a conductor when a current of one ampere dissipates one watt of power. The international volt was defined in 1893 as 1/1.434 of the emf of a Clark cell and this definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of reproducible units was abandoned in 1948. Prior to the development of the Josephson junction voltage standard, the volt was maintained in laboratories using specially constructed batteries called standard cells
33.
Geissler tube
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A Geissler tube is an early gas discharge tube used to demonstrate the principles of electrical glow discharge, similar to modern neon lighting. The tube was invented by the German physicist and glassblower Heinrich Geissler in 1857, when a high voltage is applied between the electrodes, an electrical current flows through the tube. The current dissociates electrons from the gas molecules, creating ions, and when the electrons recombine with the ions, the color of light emitted is characteristic of the material within the tube, and many different colors and lighting effects can be achieved. The first gas-discharge lamps, Geissler tubes were novelty items, made in many artistic shapes, in the early 20th century, the technology was commercialized and evolved into neon lighting. Geissler tubes were mass-produced from the 1880s as novelty and entertainment devices, with various spherical chambers, some tubes were very elaborate and complex in shape and would contain chambers within an outer casing. A novel effect could be obtained by spinning a tube at high speed with a motor. When an operating tube was touched by the hand the shape of the glowing discharge inside often changed, simple straight Geissler tubes were used in turn-of-the-century scientific research as high voltage indicators. When a Geissler tube was brought near a source of high voltage alternating current such as a Tesla coil or Ruhmkorff coil and they were used to tune the tank circuits of radio transmitters to resonance. Another example of their use was to find nodes of standing waves on transmission lines, another use c1900 was as the light source in Pulfrich refractometers. Geissler tubes are still used in physics education to demonstrate the principles of gas discharge tubes. Geissler tubes were the first gas discharge tubes, and have had a impact on the development of many instruments. One of the most significant consequences of Geissler tube technology was the discovery of the electron, by the 1870s better vacuum pumps enabled scientists to evacuate Geissler tubes to a higher vacuum, these were called Crookes tubes after William Crookes. When current was applied, it was found that the envelope of these tubes would glow at the end opposite to the cathode. In 1897 J. J. Thomson showed that cathode rays consisted of an unknown particle
34.
Neon sign
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In the signage industry, neon signs are electric signs lighted by long luminous gas-discharge tubes that contain rarefied neon or other gases. They are the most common use for lighting, which was first demonstrated in a modern form in December 1910 by Georges Claude at the Paris Motor Show. While they are used worldwide, neon signs were extremely popular in the United States from about 1920–1960, the installations in Times Square, many originally designed by Douglas Leigh, were famed, and there were nearly 2000 small shops producing neon signs by 1940. In addition to signage, neon lighting is now used frequently by artists and architects, the signage industry has declined in the past several decades, and cities are now concerned with preserving and restoring their antique neon signs. The neon sign is an evolution of the earlier Geissler tube, when a voltage is applied to electrodes inserted through the glass, an electrical glow discharge results. Geissler tubes were popular in the late 1800s, and the different colors they emitted were characteristics of the gases within. They were, however, unsuitable for lighting, the pressure of the gas inside typically declined in use. The discovery of neon in 1898 included the observation of a brilliant red glow in Geissler tubes, immediately following neons discovery, neon tubes were used as scientific instruments and novelties. From December 3–18,1910, Claude demonstrated two 12-metre long bright red neon tubes at the Paris Motor Show and this demonstration lit a peristyle of the Grand Palais. Claudes associate, Jacques Fonsèque, realized the possibilities for a business based on signage, by 1913 a large sign for the vermouth Cinzano illuminated the night sky in Paris, and by 1919 the entrance to the Paris Opera was adorned with neon tube lighting. In 1923, Georges Claude and his French company Claude Neon introduced neon gas signs to the United States by selling two to a Packard car dealership in Los Angeles, earle C. Anthony purchased the two signs reading Packard for $1,250 apiece. Neon lighting quickly became a fixture in outdoor advertising. Visible even in daylight, people would stop and stare at the first neon signs for hours, the next major technological innovation in neon lighting and signs was the development of fluorescent tube coatings. Jacques Risler received a French patent in 1926 for these, Neon signs that use an argon/mercury gas mixture emit a good deal of ultraviolet light. When this light is absorbed by a fluorescent coating, preferably inside the tube, while only a few colors were initially available to sign designers, after the Second World War phosphor materials were researched intensively for use in color televisions. About two dozen colors were available to sign designers in the 1960s, and today there are nearly 100 available colors. Neon tube signs are produced by the craft of bending glass tubing into shapes, a worker skilled in this craft is known as a glass bender, neon bender or tube bender. The neon tube is made out of 4–5 straight sticks of hollow glass sold by sign suppliers to neon shops worldwide where they are assembled into individual custom designed and fabricated lamps
35.
Ion
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An ion is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by chemical or physical means. In chemical terms, if an atom loses one or more electrons. If an atom gains electrons, it has a net charge and is known as an anion. Ions consisting of only a single atom are atomic or monatomic ions, because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of ionization of a medium, such as a gas, which are known as ion pairs are created by ion impact, and each pair consists of a free electron. The word ion comes from the Greek word ἰόν, ion, going and this term was introduced by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium. Faraday also introduced the words anion for a charged ion. In Faradays nomenclature, cations were named because they were attracted to the cathode in a galvanic device, arrhenius explanation was that in forming a solution, the salt dissociates into Faradays ions. Arrhenius proposed that ions formed even in the absence of an electric current, ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of charge to give neutral molecules or ionic salts. These stabilized species are commonly found in the environment at low temperatures. A common example is the present in seawater, which are derived from the dissolved salts. Electrons, due to their mass and thus larger space-filling properties as matter waves, determine the size of atoms. Thus, anions are larger than the parent molecule or atom, as the excess electron repel each other, as such, in general, cations are smaller than the corresponding parent atom or molecule due to the smaller size of its electron cloud. One particular cation contains no electrons, and thus consists of a single proton - very much smaller than the parent hydrogen atom. Since the electric charge on a proton is equal in magnitude to the charge on an electron, an anion, from the Greek word ἄνω, meaning up, is an ion with more electrons than protons, giving it a net negative charge. A cation, from the Greek word κατά, meaning down, is an ion with fewer electrons than protons, there are additional names used for ions with multiple charges
36.
Townsend discharge
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Those electrons are in turn accelerated and free additional electrons. The result is a multiplication that permits electrical conduction through the gas. The discharge requires a source of electrons and a significant electric field. The Townsend discharge is named after John Sealy Townsend, who discovered the fundamental ionisation mechanism by his work between 1897 and 1901, the avalanche occurs in a gaseous medium that can be ionised. The electric field and the mean path of the electron must allow free electrons to acquire an energy level that can cause impact ionisation. If the electric field is too small, then the electrons do not acquire enough energy, if the mean free path is too short, the electron gives up its acquired energy in a series of non-ionising collisions. If the mean free path is too long, then the electron reaches the anode before colliding with another molecule, the avalanche mechanism is shown in the accompanying diagram. The electric field is applied across a gaseous medium, initial ions are created with ionising radiation, an original ionisation event produces an ion pair, the positive ion accelerates towards the cathode while the free electron accelerates towards the anode. If the electric field is strong enough, the electron can gain sufficient velocity to liberate another electron when it next collides with a molecule. The two free electrons then travel towards the anode and gain sufficient energy from the field to cause further impact ionisations. This process is effectively a chain reaction that generates free electrons, the total number of electrons reaching the anode is equal to the number of collisions, plus the single initiating free electron. Initially, the number of collisions grows exponentially, the limit to the multiplication in an electron avalanche is known as the Raether limit. The Townsend avalanche can have a range of current densities. In common gas-filled tubes, such as used as gaseous ionisation detectors. Townsends early experimental apparatus consisted of parallel plates forming two sides of a chamber filled with a gas. A direct current high-voltage source was connected between the plates, the lower voltage plate being the cathode while the other was the anode, Townsend observed currents varying exponentially over ten or more orders of magnitude with a constant applied voltage when the distance between the plates was varied. He also discovered that gas pressure influenced conduction, he was able to generate ions in gases at low pressure with a lower voltage than that required to generate a spark. This observation overturned conventional thinking about the amount of current that a gas could conduct
37.
Diffusion
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Diffusion is the net movement of molecules or atoms from a region of high concentration to a region of low concentration. This is also referred to as the movement of a substance down a concentration gradient, a gradient is the change in the value of a quantity with the change in another variable. The word diffusion derives from the Latin word, diffundere, which means to spread out, a distinguishing feature of diffusion is that it results in mixing or mass transport, without requiring bulk motion. Thus, diffusion should not be confused with convection, or advection, an example of a situation in which bulk flow and diffusion can be differentiated is the mechanism by which oxygen enters the body during external respiration. The lungs are located in the cavity, which expands as the first step in external respiration. This expansion leads to an increase in volume of the alveoli in the lungs and this creates a pressure gradient between the air outside the body and the alveoli. The air moves down the gradient through the airways of the lungs and into the alveoli until the pressure of the air. The air arriving in the alveoli has a concentration of oxygen than the “stale” air in the alveoli. The increase in oxygen concentration creates a concentration gradient for oxygen between the air in the alveoli and the blood in the capillaries that surround the alveoli, oxygen then moves by diffusion, down the concentration gradient, into the blood. The other consequence of the air arriving in alveoli is that the concentration of carbon dioxide in the alveoli decreases and this creates a concentration gradient for carbon dioxide to diffuse from the blood into the alveoli. The pumping action of the heart then transports the blood around the body, as the left ventricle of the heart contracts, the volume decreases, which increases the pressure in the ventricle. This creates a gradient between the heart and the capillaries, and blood moves through blood vessels by bulk flow. The concept of diffusion is widely used in, physics, chemistry, biology, sociology, economics, however, in each case, the object that is undergoing diffusion is “spreading out” from a point or location at which there is a higher concentration of that object. In the phenomenological approach, diffusion is the movement of a substance from a region of high concentration to a region of low concentration without bulk motion, according to Ficks laws, the diffusion flux is proportional to the negative gradient of concentrations. It goes from regions of higher concentration to regions of lower concentration, some time later, various generalizations of Ficks laws were developed in the frame of thermodynamics and non-equilibrium thermodynamics. From the atomistic point of view, diffusion is considered as a result of the walk of the diffusing particles. In molecular diffusion, the molecules are self-propelled by thermal energy. Random walk of small particles in suspension in a fluid was discovered in 1827 by Robert Brown, the theory of the Brownian motion and the atomistic backgrounds of diffusion were developed by Albert Einstein
38.
Neon lighting
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Neon lighting consists of brightly glowing, electrified glass tubes or bulbs that contain rarefied neon or other gases. Neon lights are a type of cold cathode gas-discharge light, a neon tube light is a sealed glass tube with a metal electrode at each end, filled with one of a number of gases at low pressure. A high potential of several thousand volts applied to the electrodes ionizes the gas in the tube, the color of the light depends on the gas in the tube. Neon tubes can be fabricated in curving artistic shapes, to form letters or pictures and they are mainly used to make dramatic, multicolored glowing signage for advertising, called neon signs, which were popular from the 1920s to the 1950s. The term can refer to the miniature neon glow lamp, developed in 1917. While neon tube lights are typically long, the neon lamps can be less than one centimeter in length. They are still in use as indicator lights. Through the 1970s, neon lamps were widely used for numerical displays in electronics, for small decorative lamps. While these lamps are now antiques, the technology of the neon glow lamp developed into contemporary plasma displays, Neon was discovered in 1898 by the British scientists William Ramsay and Morris W. Travers. After obtaining pure neon from the atmosphere, they explored its properties using an electrical gas-discharge tube that was similar to the used for neon signs today. Georges Claude, a French engineer and inventor, presented neon tube lighting in essentially its modern form at the Paris Motor Show from December 3–18,1910. Claude, sometimes called the Edison of France, had a monopoly on the new technology. There were 2000 shops nationwide designing and fabricating neon signs, the popularity, intricacy, and scale of neon signage for advertising declined in the U. S. following the Second World War, but development continued vigorously in Japan, Iran, and some other countries. In recent decades architects and artists, in addition to sign designers, have again adopted neon tube lighting as a component in their works, Neon lighting is closely related to fluorescent lighting, which developed about 25 years after neon tube lighting. Fluorescent coatings and glasses are also an option for neon tube lighting, Neon is a noble gas chemical element and an inert gas that is a minor component of the Earths atmosphere. It was discovered in 1898 by the British scientists William Ramsay, Travers later wrote, the blaze of crimson light from the tube told its own story and was a sight to dwell upon and never forget. Immediately following neons discovery, neon tubes were used as scientific instruments, after 1902, Georges Claudes company in France, Air Liquide, began producing industrial quantities of neon as a byproduct of the air liquefaction business. From December 3–18,1910, Claude demonstrated two large, bright red neon tubes at the Paris Motor Show and these neon tubes were essentially in their contemporary form
39.
William Crookes
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Sir William Crookes OM PRS was an English chemist and physicist who attended the Royal College of Chemistry in London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes tube which was made in 1875, Crookes was the inventor of the Crookes radiometer, which today is made and sold as a novelty item. Late in life, he interested in spiritualism, and became the president of the Society for Psychical Research. Crookes made a career of being a meteorologist and fierce lecture giver at multiple studies and courses, Crookes worked in chemistry and physics. His experiments were notable for the originality of their design and his interests, ranging over pure and applied science, economic and practical problems, and psychiatric research, made him a well-known personality. He received many public and academic honors, Crookess life was one of unbroken scientific activity. William Crookes was born in London, the eldest of 16 siblings and his father, Joseph Crookes, was a tailor of north-country origin, at that time living with his second wife, Mary Scott Lewis Rutherford Johnson. From 1850 to 1854 he filled the position of assistant in the college and it wasnt in organic chemistry which the focus of his teacher, August Wilhelm von Hofmann, might have been expected to lead him towards, but into new compounds of selenium. These were the subject of his first published papers,1851, in 1855 he was appointed lecturer in chemistry at the Chester Diocesan Training College. In 1856 he married Ellen, daughter of William Humphrey of Darlington and they had three sons and a daughter. Married and living in London, he was devoted mainly to independent work, in 1859, he founded the Chemical News, a science magazine which he edited for many years and conducted on much less formal lines than was usual for the journals of scientific societies. In 1861, Crookes discovered an unknown element with a bright green emission line in its spectrum and named the element thallium, from the Greek thallos. Crookes wrote a treatise on Select Methods in Chemical Analysis in 1871. The method of analysis, introduced by Bunsen and Kirchhoff, was received by Crookes with great enthusiasm. His first important discovery was that of the element thallium, announced in 1861, by this work his reputation became firmly established, and he was elected a fellow of the Royal Society in 1863. He developed the Crookes tubes, investigating cathode rays and he published numerous papers on spectroscopy and conducted research on a variety of minor subjects. In his investigations of the conduction of electricity in low pressure gases, he discovered that as the pressure was lowered, as these examples indicate, he was a pioneer in the construction and use of vacuum tubes for the study of physical phenomena. He was, as a consequence, one of the first scientists to investigate what is now called a plasma and he also devised one of the first instruments for studying nuclear radioactivity, the spinthariscope
40.
Zinc sulfide
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Zinc sulfide is an inorganic compound with the chemical formula of ZnS. This is the form of zinc found in nature, where it mainly occurs as the mineral sphalerite. Although this mineral is black because of various impurities, the pure material is white. In its dense synthetic form, zinc sulfide can be transparent, ZnS exists in two main crystalline forms, and this dualism is often a salient example of polymorphism. In each form, the geometry at Zn and S is tetrahedral. The more stable form is known also as zinc blende or sphalerite. The hexagonal form is known as the mineral wurtzite, although it also can be produced synthetically, the transition from the sphalerite form to the wurtzite form occurs at around 1020 celsius. When silver is used as activator, the color is bright blue. Using manganese yields a color at around 590 nanometers. Copper gives long-time glow, and it has the familiar greenish glow-in-the-dark, copper-doped zinc sulfide is used also in electroluminescent panels. It also exhibits phosphorescence due to impurities on illumination with blue or ultraviolet light, zinc sulfide is also used as an infrared optical material, transmitting from visible wavelengths to just over 12 micrometers. It can be used planar as a window or shaped into a lens. It is made as microcrystalline sheets by the synthesis from hydrogen gas and zinc vapour, and this is sold as FLIR-grade. This material when hot isostatically pressed can be converted to a form known as Cleartran. Early commercial forms were marketed as Irtran-2 but this designation is now obsolete, zinc sulfide is a common pigment, sometimes called sachtolith. When combined with barium sulfate, zinc sulfide forms lithopone, fine ZnS powder is an efficient photocatalyst, which produces hydrogen gas from water upon illumination. Both sphalerite and wurtzite are intrinsic, wide-bandgap semiconductors and these are prototypical II-VI semiconductors, and they adopt structures related to many of the other semiconductors, such as gallium arsenide. The cubic form of ZnS has a gap of about 3.54 electron volts at 300 kelvin
41.
Johann Hittorf
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Johann Wilhelm Hittorf was a German physicist who was born in Bonn and died in Münster, Germany. Hittorf was the first to compute the electricity-carrying capacity of charged atoms and molecules and he formulated ion transport numbers and the first method for their measurements. He observed tubes with energy rays extending from a negative electrode and these rays produced a fluorescence when they hit the glass walls of the tubes. In 1876 the effect was named cathode rays by Eugen Goldstein, hittorfs early investigations were on the allotropes of phosphorus and selenium. Between 1853 and 1859 his most important work was on ion movement caused by electric current, in 1853 Hittorf pointed out that some ions traveled more rapidly than others. This observation led to the concept of number, the fraction of the electric current carried by each ionic species. He measured the changes in the concentration of electrolyzed solutions, computed from these the numbers of many ions. He became professor of physics and chemistry at the University of Münster and he also investigated the light spectra of gases and vapours, worked on the passage of electricity through gases, and discovered new properties of cathode rays. In 1869 he ascertained that the cathode rays glowed different colours because of different gasses and pressures and he noticed that when there was any object placed between the cathode and the illuminating side of the tube, then the shadow of that object appeared. His work led toward development of X-rays and cathode ray tubes, the measurement of current in a vacuum tube was an important step towards the creation of a vacuum tube diode. Biographical sketch and reprint of paper on migration of ions The Cathode Ray Tube site
42.
Arthur Schuster
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Schusters Integral is named after him. He contributed to making the University of Manchester a centre for the study of physics, Arthur Schuster was born in Frankfurt am Main, Germany into a family of merchants and bankers. Schusters parents were married in 1849, converted from Judaism to Christianity, in 1869, his father moved to Manchester where the family textile business was based. Arthur, who had been to school in Frankfurt and was studying in Geneva, joined his parents in 1870 and he and the other children became British citizens in 1875. From his childhood, Schuster had been interested in science and after working for a year for Schuster Brothers he persuaded his father to let him study at Owens College. He studied mathematics under Thomas Barker and physics under Balfour Stewart and he spent a year with Gustav Kirchhoff at the University of Heidelberg, and having gained his PhD, returned to Owens as an unpaid demonstrator in physics. Schuster later used his familys wealth to buy material and equipment and to endow readerships in mathematical physics at Manchester and he also contributed to the Royal Society and the International Union for Co-operation in Solar Research. This was an important appointment for such a junior scientist, on the way, he wrote a letter dated 21 February 1875, to Nature describing his observation of the green flash phenomenon. On his return to Manchester, he began research on electricity and his status there was quite unofficial, he was neither a student nor a fellow. He worked with James Clerk Maxwell and with Rayleigh, in 1881 he was appointed to the Beyer Chair of Applied Mathematics at Owens, by now one of the colleges of the new Victoria University. He succeeded his teacher Balfour Stewart as professor of physics in 1888 and this appointment gave him the opportunity to establish a large, active teaching and research department. In 1900 a new laboratory, for which he had fought and it was the fourth largest in the world. The laboratory quickly became a rival to the Cavendish, see Manchester Science Hall of Fame. Much of this later fame was associated with Ernest Rutherford who succeeded Schuster as Langworthy Professor in 1907, Schuster resigned from the chair, partly for health reasons and partly to promote the cause of international science. He ensured that Rutherford would succeed him, Schuster is credited with coining the concept of antimatter in two letters to Nature in 1898. He hypothesized antiatoms, and whole antimatter solar systems, which would yield if the atoms combined with atoms of normal matter. His hypothesis was given a mathematical foundation by the work of Paul Dirac in 1928 and he first used this form of harmonic analysis in 1897 to disprove C. G. Knotts claim of periodicity in earthquake occurrences. He went on to apply the technique to analysing sunspot activity, in 1875 Stewarts friend and Roscoes cousin, the economist Jevons, reported, Mr. Schuster is credited by Chandrasekhar to have given a fresh start to the radiative transfer problem
43.
Heinrich Hertz
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Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwells electromagnetic theory of light. The unit of frequency – cycle per second – was named the hertz in his honor, Heinrich Rudolf Hertz was born in 1857 in Hamburg, then a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family. His father Gustav Ferdinand Hertz was a barrister and later a senator and his mother was Anna Elisabeth Pfefferkorn. Hertzs paternal grandfather, Heinrich David Hertz, was a businessman and their first son, Wolff Hertz, was chairman of the Jewish community. Heinrich Rudolf Hertzs father and paternal grandparents had converted from Judaism to Christianity in 1834 and his mothers family was a Lutheran pastors family. While studying at the Gelehrtenschule des Johanneums in Hamburg, Heinrich Rudolf Hertz showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit. He studied sciences and engineering in the German cities of Dresden, Munich and Berlin, in 1880, Hertz obtained his PhD from the University of Berlin, and for the next three years remained for post-doctoral study under Helmholtz, serving as his assistant. In 1883, Hertz took a post as a lecturer in physics at the University of Kiel. In 1885, Hertz became a professor at the University of Karlsruhe. In 1886, Hertz married Elisabeth Doll, the daughter of Dr. Max Doll and they had two daughters, Johanna, born on 20 October 1887 and Mathilde, born on 14 January 1891, who went on to become a notable biologist. During this time Hertz conducted his research into electromagnetic waves. Hertz took a position of Professor of Physics and Director of the Physics Institute in Bonn on 3 April 1889, during this time he worked on theoretical mechanics with his work published in the book Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt, published posthumously in 1894. In 1892, Hertz was diagnosed with an infection and underwent operations to treat the illness and he died of granulomatosis with polyangiitis at the age of 36 in Bonn, Germany in 1894, and was buried in the Ohlsdorf Cemetery in Hamburg. Hertzs wife, Elisabeth Hertz née Doll, did not remarry, Hertz left two daughters, Johanna and Mathilde. Hertzs daughters never married and he has no descendants, Hertz always had a deep interest in meteorology, probably derived from his contacts with Wilhelm von Bezold. In 1886–1889, Hertz published two articles on what was to become known as the field of contact mechanics, joseph Valentin Boussinesq published some critically important observations on Hertzs work, nevertheless establishing this work on contact mechanics to be of immense importance. His work basically summarises how two objects placed in contact will behave under loading, he obtained results based upon the classical theory of elasticity. It was natural to neglect adhesion in that age as there were no methods of testing for it
44.
Electromagnetic radiation
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In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-, classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light through a vacuum. The oscillations of the two fields are perpendicular to other and perpendicular to the direction of energy and wave propagation. The wavefront of electromagnetic waves emitted from a point source is a sphere, the position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves are produced whenever charged particles are accelerated, and these waves can interact with other charged particles. EM waves carry energy, momentum and angular momentum away from their source particle, quanta of EM waves are called photons, whose rest mass is zero, but whose energy, or equivalent total mass, is not zero so they are still affected by gravity. Thus, EMR is sometimes referred to as the far field, in this language, the near field refers to EM fields near the charges and current that directly produced them, specifically, electromagnetic induction and electrostatic induction phenomena. In the quantum theory of electromagnetism, EMR consists of photons, quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation. The energy of a photon is quantized and is greater for photons of higher frequency. This relationship is given by Plancks equation E = hν, where E is the energy per photon, ν is the frequency of the photon, a single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light. The effects of EMR upon chemical compounds and biological organisms depend both upon the power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules, the effects of these radiations on chemical systems and living tissue are caused primarily by heating effects from the combined energy transfer of many photons. In contrast, high ultraviolet, X-rays and gamma rays are called ionizing radiation since individual photons of high frequency have enough energy to ionize molecules or break chemical bonds. These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the speed of light. Maxwell’s equations were confirmed by Heinrich Hertz through experiments with radio waves, according to Maxwells equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the field are always accompanied by a wave in the magnetic field in one direction
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Hydrogen
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Hydrogen is a chemical element with chemical symbol H and atomic number 1. With a standard weight of circa 1.008, hydrogen is the lightest element on the periodic table. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state. The most common isotope of hydrogen, termed protium, has one proton, the universal emergence of atomic hydrogen first occurred during the recombination epoch. At standard temperature and pressure, hydrogen is a colorless, odorless, tasteless, non-toxic, nonmetallic, since hydrogen readily forms covalent compounds with most nonmetallic elements, most of the hydrogen on Earth exists in molecular forms such as water or organic compounds. Hydrogen plays an important role in acid–base reactions because most acid-base reactions involve the exchange of protons between soluble molecules. In ionic compounds, hydrogen can take the form of a charge when it is known as a hydride. The hydrogen cation is written as though composed of a bare proton, Hydrogen gas was first artificially produced in the early 16th century by the reaction of acids on metals. Industrial production is mainly from steam reforming natural gas, and less often from more energy-intensive methods such as the electrolysis of water. Most hydrogen is used near the site of its production, the two largest uses being fossil fuel processing and ammonia production, mostly for the fertilizer market, Hydrogen is a concern in metallurgy as it can embrittle many metals, complicating the design of pipelines and storage tanks. Hydrogen gas is flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume. The enthalpy of combustion is −286 kJ/mol,2 H2 + O2 →2 H2O +572 kJ Hydrogen gas forms explosive mixtures with air in concentrations from 4–74%, the explosive reactions may be triggered by spark, heat, or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C, the detection of a burning hydrogen leak may require a flame detector, such leaks can be very dangerous. Hydrogen flames in other conditions are blue, resembling blue natural gas flames, the destruction of the Hindenburg airship was a notorious example of hydrogen combustion and the cause is still debated. The visible orange flames in that incident were the result of a mixture of hydrogen to oxygen combined with carbon compounds from the airship skin. H2 reacts with every oxidizing element, the ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 91 nm wavelength. The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, however, the atomic electron and proton are held together by electromagnetic force, while planets and celestial objects are held by gravity. The most complicated treatments allow for the effects of special relativity
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Subatomic particle
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In the physical sciences, subatomic particles are particles much smaller than atoms. There are two types of particles, elementary particles, which according to current theories are not made of other particles. Particle physics and nuclear physics study these particles and how they interact, in particle physics, the concept of a particle is one of several concepts inherited from classical physics. But it also reflects the understanding that at the quantum scale matter. The idea of a particle underwent serious rethinking when experiments showed that light could behave like a stream of particles as well as exhibit wave-like properties and this led to the new concept of wave–particle duality to reflect that quantum-scale particles behave like both particles and waves. Another new concept, the uncertainty principle, states that some of their properties taken together, such as their simultaneous position and momentum, in more recent times, wave–particle duality has been shown to apply not only to photons but to increasingly massive particles as well. Interactions of particles in the framework of field theory are understood as creation and annihilation of quanta of corresponding fundamental interactions. This blends particle physics with field theory, any subatomic particle, like any particle in the 3-dimensional space that obeys laws of quantum mechanics, can be either a boson or a fermion. Various extensions of the Standard Model predict the existence of a graviton particle. Composite subatomic particles are bound states of two or more elementary particles, for example, a proton is made of two up quarks and one down quark, while the atomic nucleus of helium-4 is composed of two protons and two neutrons. The neutron is made of two quarks and one up quark. Composite particles include all hadrons, these include baryons and mesons, in special relativity, the energy of a particle at rest equals its mass times the speed of light squared, E = mc2. That is, mass can be expressed in terms of energy, if a particle has a frame of reference where it lies at rest, then it has a positive rest mass and is referred to as massive. Baryons tend to have greater mass than mesons, which in turn tend to be heavier than leptons and it is also certain that any particle with an electric charge is massive. These include the photon and gluon, although the latter cannot be isolated, through the work of Albert Einstein, Satyendra Nath Bose, Louis de Broglie, and many others, current scientific theory holds that all particles also have a wave nature. This has been verified not only for elementary particles but also for compound particles like atoms, interactions between particles have been scrutinized for many centuries, and a few simple laws underpin how particles behave in collisions and interactions. These are the basics of Newtonian mechanics, a series of statements and equations in Philosophiae Naturalis Principia Mathematica. The negatively charged electron has an equal to 1⁄1837 or 1836 of that of a hydrogen atom
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