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Glow Discharge
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 the low-pressure gas. When the voltage exceeds a certain value called the striking voltage , the gas in the tube ionizes , becoming a plasma, and begins conducting electricity, causing it to glow with a colored light. The color depends on the gas used. Glow discharge
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 with spectroscopy can reveal much about the atomic interactions in the gas, so glow discharge is used in plasma physics and analytical chemistry . It is also used in the surface treatment technique called sputtering
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Atomic Spectroscopy
ATOMIC SPECTROSCOPY is the study of the electromagnetic radiation absorbed and emitted by atoms. Since unique elements have characteristic (signature) spectra, atomic spectroscopy, specifically the electromagnetic spectrum or mass spectrum , is applied for determination of elemental compositions. It can be divided by atomization source or by the type of spectroscopy used. In the latter case, the main division is between optical and mass spectrometry. Mass spectrometry generally gives significantly better analytical performance, but is also significantly more complex. This complexity translates into higher purchase costs, higher operational costs, more operator training, and a greater number of components that can potentially fail. Because optical spectroscopy is often less expensive and has performance adequate for many tasks, it is far more common Atomic absorption spectrometers are one of the most commonly sold and used analytical devices
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Chemical Element
A CHEMICAL ELEMENT or ELEMENT is a species of atoms having the same number of protons in their atomic nuclei (i.e. the same atomic number , or Z). There are 118 elements that have been identified, of which the first 94 occur naturally on Earth
Earth
with the remaining 24 being synthetic elements . There are 80 elements that have at least one stable isotope and 38 that have exclusively radioactive isotopes , which decay over time into other elements. Iron
Iron
is the most abundant element (by mass ) making up Earth, while oxygen is the most common element in the Earth\'s crust . Chemical elements constitute all of the ordinary matter of the universe. However astronomical observations suggest that ordinary observable matter makes up only about 15% of the matter in the universe: the remainder is dark matter ; the composition of this is unknown, but it is not composed of chemical elements
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William Crookes
SIR WILLIAM CROOKES OM PRS (/krʊks/ ; 17 June 1832 – 4 April 1919) 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
Crookes tube
which was made in 1875. Crookes was the inventor of the Crookes radiometer
Crookes radiometer
, which today is made and sold as a novelty item. Late in life, he became interested in spiritualism , and became the president of the Society for Psychical Research . CONTENTS* 1 Biography * 1.1 Early years * 1.2 Middle years * 1.3 Later years * 2 Spiritualism
Spiritualism
* 3 References * 4 Further reading * 5 External links BIOGRAPHYCrookes made a career of being a meteorologist and fierce lecturer for multiple studies and courses. Crookes worked in chemistry and physics
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Bremsstrahlung Radiation
BREMSSTRAHLUNG (German pronunciation: ( listen ), from bremsen "to brake" and Strahlung "radiation"; i.e., "braking radiation" or "deceleration radiation") is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus . The moving particle loses kinetic energy , which is converted into a photon , thus satisfying the law of conservation of energy . The term is also used to refer to the process of producing the radiation. Bremsstrahlung
Bremsstrahlung
has a continuous spectrum , which becomes more intense and whose peak intensity shifts toward higher frequencies as the change of the energy of the decelerated particles increases. Broadly speaking, bremsstrahlung or BRAKING RADIATION is any radiation produced due to the deceleration (negative acceleration) of a charged particle, which includes synchrotron radiation (i.e
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Excited State
In quantum mechanics , an EXCITED STATE of a system (such as an atom , molecule or nucleus ) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being raised to an excited state. The temperature of a group of particles is indicative of the level of excitation (with the notable exception of systems that exhibit negative temperature ). The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy (such as a photon or a phonon ) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state)
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Anode
An ANODE is an electrode through which conventional current flows into a polarized electrical device. A common mnemonic is ACID for "anode current into device". The direction of (positive) electric current is opposite to the direction of electron flow: (negatively charged) electrons flow out the anode to the outside circuit. CONTENTS * 1 Charge flow * 2 Examples * 3 Etymology * 4 Electrolytic anode * 5 Battery or galvanic cell anode * 6 Vacuum tube anode * 7 Diode
Diode
anode * 8 Sacrificial anode
Sacrificial anode
* 9 Related antonym * 10 See also * 11 References * 12 External links CHARGE FLOWThe terms anode and cathode do not relate to the voltage polarity of those electrodes but the direction of the current: whether positive charge is flowing into or out of the device. Conventional current quantifies the flow of positive charge
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Alternating Current
ALTERNATING CURRENT (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction. Alternating current
Alternating current
is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances , televisions and electric lamps into a wall socket . A common source of DC power is a battery cell in a flashlight . The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage . The usual waveform of alternating current in most electric power circuits is a sine wave . In certain applications, different waveforms are used, such as triangular or square waves
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Ionized
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 subatomic particles , collisions with other atoms, molecules and ions, or through the interaction with light. Heterolytic bond cleavage and heterolytic substitution reactions can result in the formation of ion pairs. Ionization
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
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Gamma Ray
GAMMA RAYS (also called GAMMA RADIATION), denoted by the lower-case Greek letter gamma (γ or {displaystyle gamma } ), are penetrating electromagnetic radiation of a kind arising from the radioactive decay of atomic nuclei . It consists of photons in the highest observed range of photon energy . Paul Villard , a French chemist and physicist , discovered gamma radiation in 1900 while studying radiation emitted by radium . In 1903, Ernest Rutherford named this radiation gamma rays. Rutherford had previously discovered two other types of radioactive decay, which he named alpha and beta rays . Gamma rays are able to ionize other atoms (ionizing radiation ), and are thus biologically hazardous. The decay of an atomic nucleus from a high energy state to a lower energy state, a process called gamma decay, produces gamma radiation
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Cathode
A CATHODE is the electrode from which a conventional current leaves a polarized electrical device. (This definition can be recalled by using the mnemonic CCD for cathode current departs.) 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 electrons flow into the device's cathode. Cathode
Cathode
polarity with respect to the anode can be positive or negative; it depends on how the device operates
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Quantum
In physics , a QUANTUM (plural: QUANTA) is the minimum amount of any physical entity involved in an interaction. The fundamental notion that a physical property may be "quantized" is referred to as "the hypothesis of quantization ". This means that the magnitude of the physical property can take on only certain discrete values. For example, a photon is a single quantum of light (or of any other form of electromagnetic radiation ), and can be referred to as a "light quantum". Similarly, the energy of an electron bound within an atom is also quantized, and thus can only exist in certain discrete values. The fact that electrons can only exist at discrete energy levels in an atom causes atoms to be stable, and hence matter in general is stable. Quantization is one of the foundations of the much broader physics of quantum mechanics
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Ablation
ABLATION is removal of material from the surface of an object by vaporization , chipping, or other erosive processes. Examples of ablative materials are described below, and include spacecraft material for ascent and atmospheric reentry , ice and snow in glaciology , biological tissues in medicine and passive fire protection materials. CONTENTS * 1 Biology * 2 Glaciology * 3 Laser ablation * 4 Marine surface coatings * 5 Medicine
Medicine
* 6 Passive fire protection * 7 Spaceflight * 8 See also * 9 References * 10 External links BIOLOGYBIOLOGICAL ABLATION is the removal of a biological structure or functionality. Genetic ablation is another term for gene silencing , in which gene expression is abolished through the alteration or deletion of genetic sequence information. In cell ablation, individual cells in a population or culture are destroyed or removed
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Voltage-regulator Tube
A VOLTAGE-REGULATOR TUBE (VR TUBE) is an electronic component used as a shunt regulator to hold a voltage constant at a pre-determined level. Physically, these devices resemble vacuum tubes , but there are two main differences: * Their glass envelopes are filled with a gas mixture, and * They have a cold cathode ; the cathode is not heated with a filament to emit electrons.Electrically, these devices resemble Zener diodes , with the following major differences: * They rely on gas ionization , rather than Zener breakdown
Zener breakdown
* The unregulated supply voltage must be 15–20% above the nominal output voltage to ensure that the discharge starts * The output can be higher than nominal if the current through the tube is too low.When sufficient voltage is applied across the electrodes, the gas ionizes , forming a glow discharge around the cathode electrode
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Electric Spark
An ELECTRIC SPARK is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized , electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael Faraday described this phenomenon as "the beautiful flash of light attending the discharge of common electricity." The rapid transition from a non-conducting to a conductive state produces a brief emission of light and a sharp crack or snapping sound. A spark is created when the applied electric field exceeds the dielectric breakdown strength of the intervening medium. For air, the breakdown strength is about 30 kV/cm at sea level. At the beginning stages, free electrons in the gap (from cosmic rays or background radiation ) are accelerated by the electrical field. As they collide with air molecules, they create additional ions and newly freed electrons which are also accelerated
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Electrical Breakdown
ELECTRICAL BREAKDOWN or DIELECTRIC BREAKDOWN is when current flows through an electrical insulator when the voltage applied across it exceeds the breakdown voltage . This results in the insulator becoming electrically conductive . Electrical breakdown
Electrical breakdown
may be a momentary event (as in an electrostatic discharge ), or may lead to a continuous arc if protective devices fail to interrupt the current in a power circuit. Under sufficient electrical stress, electrical breakdown can occur within solids, liquids, gases or vacuum
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