bioelectricity: …a flattened cell called an electroplaque. Large numbers of electroplaques are arranged in series and in parallel to build up voltage and current-producing capacity of the electric organ. Fishes deliver a sudden discharge of electricity by timing the nervous impulses that activate individual electroplaques, thereby providing simultaneous action of the…

electrode, electric conductor, usually metal, used as either of the two terminals of an electrically conducting medium; it conducts current into and out of the medium, which may be an electrolytic solution as in a storage battery, or a solid, gas, or vacuum. The electrode from which electrons

spectroscopy: Line sources: …are hollow cathode lamps and electrodeless lamps driven by microwave radiation. If specific atomic lines are desired, a small amount of the desired element is introduced in the discharge.

integrated circuit: Chemical methods: …chemical methods of deposition are electrodeposition (or electroplating) and thermal oxidation. In the former the substrate is given an electrically conducting coating and placed in a liquid solution (electrolyte) containing metal ions, such as gold, copper, or nickel. A wide range of film thicknesses can be built. In thermal oxidation…

psychogalvanic reflex (PGR), a change in the electrical properties of the body (probably of the skin) following noxious stimulation, stimulation that produces emotional reaction, and, to some extent, stimulation that attracts the subject’s attention and leads to an aroused alertness. The response

separation and purification: Barrier separations: In electrodialysis, an electrical field accelerates the migration.

electrochemical reaction: History: …the transfer of electrons (called electrodics), gained in importance and became the main aspect of electrochemistry. From about 1960, electrodics began to develop as an interdisciplinary area in the search for solutions to problems such as the source of energy in space flights from fuel cells, the stability of metals…

machine tool: Electrical-discharge machining (EDM): EDM involves the direction of high-frequency electrical spark discharges from a graphite or soft metal tool, which serves as an electrode, to disintegrate electrically conductive materials such as hardened steel or carbide. The electrode and workpiece are immersed in a dielectric liquid, and…

ammeter: The electrodynamic ammeter uses a moving coil rotating in the field produced by a fixed coil. It measures direct and alternating current (by using a rectifier to convert the AC to DC) with accuracies of 0.1 to 0.25 percent. In the thermal (or hot-wire) ammeter, used…

maglev: Electromagnetic suspension (EMS) and electrodynamic suspension (EDS): Electrodynamic suspension (EDS) systems are similar to EMS in several respects, but the magnets are used to repel the train from the guideway rather than attract them. These magnets are supercooled and superconducting and have the ability to conduct electricity for a short time after…

transducer, device that converts input energy into output energy, the latter usually differing in kind but bearing a known relation to input. Originally, the term referred to a device that converted mechanical stimuli into electrical output, but it has been broadened to include devices that sense

electromagnetism: Foundations of electrochemistry and electrodynamics: The invention of the battery in 1800 made possible for the first time major advances in the theories of electric current and electrochemistry. Both science and technology developed rapidly as a direct result,

electroencephalography, technique for recording and interpreting the electrical activity of the brain. The nerve cells of the brain generate electrical impulses that fluctuate rhythmically in distinct patterns. In 1929 German scientist Hans Berger published the results of the first study to employ

electroencephalography, technique for recording and interpreting the electrical activity of the brain. The nerve cells of the brain generate electrical impulses that fluctuate rhythmically in distinct patterns. In 1929 German scientist Hans Berger published the results of the first study to employ

electrophotography: A proprietary process known as Electrofax employs a photographic paper coated with a dielectric layer; the entire charging, exposure, and development process is thus effected directly on the paper itself.

electroforming, making duplicates by electroplating metal onto a mold of an object, then removing the mold. Intricate surface details are exactly reproduced by this process, which is used to make masters for pressing phonograph records. Electroforming is also used for reproducing medals and for

colorectal cancer: Treatment: …them in a procedure called electrofulguration. In cases where the lower portion of the rectum is involved, a colostomy may be required, whereby the surgeon creates an artificial opening for the removal of waste. If colorectal cancer has spread to surrounding tissues such as those of the uterus, prostate, liver,…

steel: Surface coating: Electrolytic galvanizing lines have similar entry and exit sections, but they deposit zinc in as many as 20 consecutive electrolytic coating cells. Of the several successful cell designs, the simple vertical cell (B in the figure) is discussed here to explain the principle. The strip,…

electrogasdynamics, study of the forces produced by the motion of electrically charged particles (ions) carried by an insulating gas flowing through an electric field. See also magnetohydrodynamic power

chemical analysis: Electrogravimetry: This method employs an electric current to deposit a solid on an electrode from a solution. Normally the deposit is a metallic plate that has formed from the corresponding metallic ions in the solution; however, other electrode coatings also can be formed. The use…

virtual sit-in: …Disturbance Theater, the Electrohippies (now Electrohippies Collective), and RTMark—were known for their “hactivism.” In 1998 Electronic Disturbance Theater held one of the first virtual sit-ins. The action was in solidarity with the Zapatista National Liberation Army (EZLN), a Mexican guerrilla group, and was directed against the Mexican government. The Electrohippies,…

electrojet, streaming movement of charged particles in the lower ionosphere. The term is limited by some to those flow patterns that contain a significant proportion of neutral gases, but highly concentrated, laterally limited, electric currents are also called electrojets. The latter circulate

electroless plating, nonelectrical plating of metals and plastics to achieve uniform coatings by a process of controlled autocatalytic (self-continuing) reduction. Discovered in 1944 by A. Brenner and G.E. Riddell, electroless plating involves the deposition of such metals as copper, nickel,

electroluminescence, production of light by the flow of electrons, as within certain crystals. Electroluminescence is one of the few instances in which a direct conversion of electric energy into visible light takes place without the generation of heat, such as occurs in the incandescent lamp.

lamp: Modern electrical light sources: The electroluminescent lamp, another semiconductor lamp, consists of a flat-plate capacitor with a phosphor (similar to those used with fluorescent lamps) in the dielectric; it is used with alternating current. These lamps are used for night-lights and engineering applications such as luminous instrument panels.

electrolysis, process by which electric current is passed through a substance to effect a chemical change. The chemical change is one in which the substance loses or gains an electron (oxidation or reduction). The process is carried out in an electrolytic cell, an apparatus consisting of positive

electrolyte, in chemistry and physics, substance that conducts electric current as a result of a dissociation into positively and negatively charged particles called ions, which migrate toward and ordinarily are discharged at the negative and positive terminals (cathode and anode) of an electric

burn: …salts, not only disturbs their balance in the body but changes the osmotic balance of the blood and body fluids. The significance of these physiological changes was understood in 1905, but not until the 1930s were doctors able to correct them with transfusions of blood or plasma.

electrolytic cell, any device in which electrical energy is converted to chemical energy, or vice versa. Such a cell typically consists of two metallic or electronic conductors (electrodes) held apart from each other and in contact with an electrolyte (q.v.), usually a dissolved or fused ionic

conductive ceramics: Ionic conduction consists of the transit of ions (atoms of positive or negative charge) from one site to another via point defects called vacancies in the crystal lattice. At normal ambient temperatures very little ion hopping takes place, since the atoms are at relatively low…

electrolyte, in chemistry and physics, substance that conducts electric current as a result of a dissociation into positively and negatively charged particles called ions, which migrate toward and ordinarily are discharged at the negative and positive terminals (cathode and anode) of an electric

chemical analysis: Electrogravimetry: This method employs an electric current to deposit a solid on an electrode from a solution. Normally the deposit is a metallic plate that has formed from the corresponding metallic ions in the solution; however, other electrode coatings also can be formed. The use…

acid–base reaction: Hydrogen and hydroxide ions: …with the advent of the electrolytic dissociation theory propounded by Wilhelm Ostwald and Svante August Arrhenius (both Nobel laureates) in the 1880s. The principal feature of this theory is that certain compounds, called electrolytes, dissociate in solution to give ions. With the development of this theory it was realized that…

steel: Surface coating: Electrolytic galvanizing lines have similar entry and exit sections, but they deposit zinc in as many as 20 consecutive electrolytic coating cells. Of the several successful cell designs, the simple vertical cell (B in the figure) is discussed here to explain the principle. The strip,…

electropolishing, electrochemical process of smoothing a metallic surface. The metallic object is made the anode in an electrolytic reaction so controlled that its high spots dissolve, until only a smooth surface remains. Electropolishing is the reverse of the process of

metallurgy: Extractive metallurgy: …from one electrode of an electrolytic cell and its deposition in a purer form onto the other electrode. Chemical refining involves either the condensation of metal from a vapour or the selective precipitation of metal from an aqueous solution.

metallurgy: Electrolytic smelting: Smelting is also carried out by the electrolytic dissociation, at high temperatures, of a liquid metallic chloride compound (as is done with magnesium) or of a metallic oxide powder dissolved in molten electrolyte (as is done with aluminum). In each case, electric current…

liquid: Classes of solutions: Broadly speaking, liquid mixtures can be classified as either solutions of electrolytes or solutions of nonelectrolytes. Electrolytes are substances that can dissociate into electrically charged particles called ions, while nonelectrolytes consist

electromagnet, device consisting of a core of magnetic material surrounded by a coil through which an electric current is passed to magnetize the core. An electromagnet is used wherever controllable magnets are required, as in contrivances in which the magnetic flux is to be varied, reversed, or

warship: Large carriers: …mainly to accommodate the revolutionary electromagnetic aircraft launch system, or EMALS. EMALS replaced the classic steam-powered catapult with a 100-metre- (330-foot-) long "linear synchronous motor," an electric motor containing a series of magnetic coils that accelerated the launcher and connected aircraft along the carrier’s deck. Electromagnetic launching reduced stress on…

speed of light, speed at which light waves propagate through different materials. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 metres per second. The speed of light is considered a fundamental constant of nature. Its significance is far broader

electromagnetic field, a property of space caused by the motion of an electric charge. A stationary charge will produce only an electric field in the surrounding space. If the charge is moving, a magnetic field is also produced. An electric field can be produced also by a changing magnetic field.

electromagnetism, science of charge and of the forces and fields associated with charge. Electricity and magnetism are two aspects of electromagnetism. Electricity and magnetism were long thought to be separate forces. It was not until the 19th century that they were finally treated as interrelated

electron microscope: Operating principles: …lenses, but modern instruments use electromagnetic lenses. These consist of a solenoid of wire together with a magnetic pole piece that creates and concentrates a magnetic field. The lenses used for the condenser and projector system of the microscope differ from the objective lens only in details. For example, the…

electromechanical transducer: Electromagnetic speakers: Most loudspeakers are of the electromagnetic, or dynamic, variety, in which a voice coil moves in the gap of a permanent magnet when a time-varying current flows through the coil. The magnet is generally in the shape of a “W” or a ring.…

oscillograph: …in common use are the electromagnetic oscillograph and the cathode-ray oscillograph; the latter is also known as a cathode-ray oscilloscope (q.v.), which, strictly speaking, is purely an indicating instrument, while the oscillograph can make permanent records.

superconductivity: Discovery: …predicted the existence of an electromagnetic penetration depth, which was first confirmed experimentally in 1939. In 1950 it was clearly shown for the first time that a theory of superconductivity must take into account the fact that free electrons in a crystal are influenced by the vibrations of atoms that…

electromagnetic spectrum: …subranges, commonly referred to as portions, such as visible light or ultraviolet radiation. The various portions bear different names based on differences in behaviour in the emission, transmission, and absorption of the corresponding waves and also based on their different practical applications. There are no precise accepted boundaries between any…

pump: Electromagnetic pumps.: These can be used only to pump fluids that are good electrical conductors. The pipe carrying the fluid is placed in a magnetic field and a current passed crosswise through the fluid, so that it is subjected to an electromagnetic force in the…

electromagnetic radiation, in classical physics, the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays. In such a wave,

electromechanical transducer: Electromagnetic speakers: Most loudspeakers are of the electromagnetic, or dynamic, variety, in which a voice coil moves in the gap of a permanent magnet when a time-varying current flows through the coil. The magnet is generally in the shape of a “W” or a ring.…

electromagnetic spectrum, the entire distribution of electromagnetic radiation according to frequency or wavelength. Although all electromagnetic waves travel at the speed of light in a vacuum, they do so at a wide range of frequencies, wavelengths, and photon energies. The electromagnetic spectrum

maglev: Electromagnetic suspension (EMS) and electrodynamic suspension (EDS): Electromagnetic suspension (EMS) uses the attractive force between magnets present on the train’s sides and underside and on the guideway to levitate the train. A variation on EMS, called Transrapid, employs an electromagnet to lift the train off the guideway. The attraction from magnets present…

Oliver Heaviside: In Electromagnetic Theory (1893–1912), he postulated that an electric charge would increase in mass as its velocity increases, an anticipation of an aspect of Einstein’s special theory of relativity. When wireless telegraphy proved effective over long distances, Heaviside theorized that a conducting layer of the atmosphere…

railroad: Brake systems: …sets is supplemented by fitting electromagnetic track brakes to car trucks. Activated at the start of deceleration from high speed, these retard by the frictional resistance generated when bar magnets are lowered into contact with the rails. Some Shinkansen train-sets have eddy current instead of electromagnetic track brakes. The eddy-current…

transducer: These operate on electromagnetic principles.

electromagnetic radiation, in classical physics, the flow of energy at the universal speed of light through free space or through a material medium in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays. In such a wave,

fusion reactor: Plasma heating: …methods have been highly developed: electromagnetic wave heating and neutral-beam injection heating. In the former, electromagnetic waves are directed by antennas at the surface of the plasma. The waves penetrate the plasma and transfer their energy to the constituent particles. Ionized gases can support the propagation of a remarkably large…

electromagnetism, science of charge and of the forces and fields associated with charge. Electricity and magnetism are two aspects of electromagnetism. Electricity and magnetism were long thought to be separate forces. It was not until the 19th century that they were finally treated as interrelated

photoengraving: Electromechanical plate making: While these developments in chemical etching were taking place, other experiments were being conducted to assess the feasibility of replacing traditional methods with the techniques of electronics, optics, and mechanics. The first successful result of these efforts was a device, introduced in…

telephone: Electromechanical switching: The idea of automatic switching appeared as early as 1879, and the first fully automatic switch to achieve commercial success was invented in 1889 by Almon B. Strowger, the owner of an undertaking business in Kansas City, Missouri. The Strowger switch consisted of…

electromechanical transducer, any type of device that either converts an electrical signal into sound waves (as in a loudspeaker) or converts a sound wave into an electrical signal (as in the microphone). Many of the transducers used in everyday life operate in both directions, such as the

metallurgy: Extractive metallurgy: …lower or controlled by pyrometallurgical, electrolytic, or chemical means. Pyrometallurgical refining usually consists of the oxidizing of impurities in a high-temperature liquid bath. Electrolysis is the dissolving of metal from one electrode of an electrolytic cell and its deposition in a purer form onto the other electrode. Chemical refining involves…

electrometer, instrument designed to measure very small voltages and currents. The quadrant, Lindermann, Hoffman, and Wulf electrometers measure electrical potential between charged elements (e.g., plates or fine quartz fibres) within the housings of the electrometer. The sensitivity of these

electromotive force, energy per unit electric charge that is imparted by an energy source, such as an electric generator or a battery. Energy is converted from one form to another in the generator or battery as the device does work on the electric charge being transferred within itself. One

electromotive series, listing of chemical species (atoms, molecules, and ions) in the order of their tendency to gain or lose electrons (be reduced or oxidized, respectively), expressed in volts and measured with reference to the hydrogen electrode, which is taken as a standard and arbitrarily

electromyography, the graphing and study of the electrical characteristics of muscles. Resting muscle is normally electrically silent. However, when it is active, as during contraction or stimulation, an electrical current is generated, and the successive action potentials (impulses) can be

electromyography, the graphing and study of the electrical characteristics of muscles. Resting muscle is normally electrically silent. However, when it is active, as during contraction or stimulation, an electrical current is generated, and the successive action potentials (impulses) can be

electron, one of the three basic subatomic particles—along with protons and neutrons—that make up atoms, the basic building blocks of all matter and chemistry. The negatively charged electrons circle an atom’s central nucleus, which is formed by positively charged protons and the electrically

particle accelerator: Linear electron accelerators: The force that acts on electrons in a traveling-wave accelerator is provided by an electromagnetic field with a frequency near 3,000 MHz (1 MHz = 1,000,000 Hertz, or 1,000,000 cycles per second)—a microwave. The acceleration chamber is an evacuated cylindrical pipe that…

electron affinity, in chemistry, the amount of energy liberated when an electron is added to a neutral atom to form a negatively charged ion. The electron affinities of atoms are difficult to measure, hence values are available for only a few chemical elements, chiefly the halogens. These values

electron beam, stream of electrons (as from a betatron) generated by heat (thermionic emission), bombardment of charged atoms or particles (secondary electron emission), or strong electric fields (field emission). Electrons may be collimated by holes and slits, and, because they are electrically

3D printing: …is electron beam melting (EBM); here the laser apparatus is replaced by an electron gun, which focuses a powerful electrically charged beam onto the powder under vacuum conditions. The most-advanced DMLS and EBM processes can make final products of advanced steel, titanium, and cobalt-chromium alloys.

electron capture, one of three processes of radioactive disintegration known as beta decay

electron charge, (symbol e), fundamental physical constant expressing the naturally occurring unit of electric charge, equal to 1.602176634 × 10−19 coulomb. In addition to the electron, all freely existing charged subatomic particles thus far discovered have an electric charge equal to this value

electronic configuration, the arrangement of electrons in orbitals around an atomic nucleus. The electronic configuration of an atom in the quantum-mechanical model is stated by listing the occupied orbitals, in order of filling, with the number of electrons in each orbital indicated by

crystal: Metallic bonds: The phrase electron correlation describes the correlated movements of the electrons; the motion of each electron depends on the positions of neighbouring electrons. Electrons have strong short-range order with one another. Correlation ensures that each unit cell in the crystal has, on the average, the number of…

spectroscopy: Electronic transitions: This difference, the electron correlation energy, can be a substantial fraction of the total energy.

fusion reactor: Plasma heating: Similarly, electron cyclotron resonance heating may be used to heat electrons. Such electron heating requires very high frequencies (tens to hundreds of gigahertz), such as produced by free-electron lasers and gyrotron tubes.

plasma: Higher frequency waves: …these two waves (called the electron cyclotron and ion cyclotron waves, respectively) cause electron and cyclotron resonances (synchronization) at the appropriate resonance frequencies. Beyond these resonances, transverse wave propagation does not occur at all until frequencies comparable to and above the plasma frequency are reached.

electron diffraction, interference effects owing to the wavelike nature of a beam of electrons when passing near matter. According to the proposal (1924) of the French physicist Louis de Broglie, electrons and other particles have wavelengths that are inversely proportional to their momentum.

oxide: Carbon monoxide: …also useful as a metallurgical reducing agent, because at high temperatures it reduces many metal oxides to the elemental metal. For example, copper(II) oxide, CuO, and iron(III) oxide, Fe2O3, are both reduced to the metal by carbon monoxide.

electricity: Thermionic emission: A metal contains mobile electrons in a partially filled band of energy levels—i.e., the conduction band. These electrons, though mobile within the metal, are rather tightly bound to it. The energy that is required to release a mobile electron from the metal varies from about 1.5 to 6 electron…

radioactivity: Beta-minus decay: In beta-minus decay, an energetic negative electron is emitted, producing a daughter nucleus of one higher atomic number and the same mass number. An example is the decay of the uranium daughter product thorium-234 into protactinium-234:

spectroscopy: …surface analysis technique known as electron energy loss spectroscopy (EELS) that measures the energy lost when low-energy electrons (typically 5–10 electron volts) collide with a surface. Occasionally, the colliding electron loses energy by exciting the surface; by measuring the electron’s energy loss, vibrational excitations associated with the surface can be…

crystal: Antiferromagnetic materials: The exchange interaction between ions in this case has the opposite sign and favours the alternate arrangements of spins. The sign of the exchange interaction between ions depends on the length of the covalent bond and the bonding angles; it may have either orientation. The characteristic…

electron tube: Energy transfer: …will increase (amplification) if the electrons lose kinetic energy, and, conversely, it will decrease if the electrons gain kinetic energy.

electron gun, electrode structure that produces and may control, focus, and deflect a beam of electrons, as in a television picture tube (see figure), where the beam produces a visual pattern on the tube’s screen. The source of the electron beam is the cathode, a flat metal support covered with

electron gun, electrode structure that produces and may control, focus, and deflect a beam of electrons, as in a television picture tube (see figure), where the beam produces a visual pattern on the tube’s screen. The source of the electron beam is the cathode, a flat metal support covered with

hole, in condensed-matter physics, the name given to a missing electron in certain solids, especially semiconductors. Holes affect the electrical, optical, and thermal properties of the solid. Along with electrons, they play a critical role in modern digital technology when they are introduced into

particle accelerator: Linear electron accelerators: The force that acts on electrons in a traveling-wave accelerator is provided by an electromagnetic field with a frequency near 3,000 MHz (1 MHz = 1,000,000 Hertz, or 1,000,000 cycles per second)—a microwave. The acceleration chamber is an evacuated cylindrical pipe that…

electron-probe microanalyzer, type of electron microscope used to provide chemical information. (A limitation of the conventional electron microscope is that it provides no elemental analysis.) Electron-probe microanalyzers have been developed since 1947 to carry out nondestructive elemental

electron microscope, microscope that attains extremely high resolution using an electron beam instead of a beam of light to illuminate the object of study. Fundamental research by many physicists in the first quarter of the 20th century suggested that cathode rays (i.e., electrons) might be used in

electron microscopy, Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power. To make them more observable, samples may be coated with metal atoms. Because electrons

mass spectrometry: Electron multipliers: The development of electronic techniques for television during the 1930s yielded a device of extraordinary sensitivity for measuring small electron beams—namely, the secondary electron multiplier. Although originally invented for the amplification of the tiny currents from a photocathode, it soon proved to be…

neutrino: The basic properties of the electron-neutrino—no electric charge and little mass—were predicted in 1930 by the Austrian physicist Wolfgang Pauli to explain the apparent loss of energy in the process of radioactive beta decay. The Italian-born physicist Enrico Fermi further elaborated (1934) the theory of beta decay and gave the

electron optics, branch of physics that is concerned with beams of electrons, their deflection and focusing by electric and magnetic fields, their interference when crossing each other, and their diffraction or bending when passing very near matter or through the spacings in its submicroscopic

electrophile: …atom or molecule containing an electron pair available for bonding. Electrophilic substances are Lewis acids (compounds that accept electron pairs), and many of them are Brønsted acids (compounds that donate protons). Examples of electrophiles are hydronium ion (H3O+, from Brønsted acids), boron trifluoride (BF3), aluminum chloride (AlCl3), and the halogen…

electron paramagnetic resonance (EPR), selective absorption of weak radio-frequency electromagnetic radiation (in the microwave region) by unpaired electrons in the atomic structure of certain materials that simultaneously are subjected to a constant, strong magnetic field. The unpaired electrons,

chemical analysis: Microwave absorptiometry: …for nuclear magnetic resonance spectrometry, electron spin resonance spectrometry is used to study spinning electrons. The absorbed radiation falls in the microwave spectral region and induces transitions in the spin states of the electrons. An externally applied magnetic field is required. The technique is effective for studying structures and reactions…