lead too short date August 2011 Electromagnetism cTopic Magnetostatics Electriccurrent is a flow of electric ... is charge flowing through some surface at the rate of one coulomb per second. Electriccurrent is measured ... when discussing the value of an electriccurrent, especially in older texts modern practice often ... I math symbol was used by Andr Marie Amp re , after whom the unit of electriccurrent is named, in formulating ... . In other media, any stream of charged objects may constitute an electriccurrent. To provide a definition ... materials, the electriccurrent is due to the flow of both positively and negatively charged particles ... and in certain solid electrolytes, the electriccurrent is entirely composed of flowing ions. In a semiconductor ... of the force, thus forming what we call an electriccurrent. When a metal wire is connected across ... conductor. For an electriccurrent of 1 ampere, 1 coulomb of electric charge which consists of about ..., I is in amperes. More generally, electriccurrent can be represented as the rate at which charge ... of an electriccurrent. It is defined as a Vector geometric vector whose magnitude is the electric ... is a Scalar mathematics scalar that represents the electriccurrent. Current density current per ... , , math where math I math is the electriccurrent math n math is number of charged particles per ... charge, and therefore any changing electriccurrent, gives rise to an Electromagnetism electromagnetic ... law Amp re s law , an electriccurrent produces a magnetic field . Electriccurrent produces ... the wire. Electriccurrent can be directly measured with a galvanometer , but this method involves ... in the opposite direction of the conventional electriccurrent. File Battery symbol2.svg thumb right ... gives the same electriccurrent, and has the same effect in a circuit, as an equal flow of negative ... opposite to that of conventional or electriccurrent. Reference direction When analyzing electrical ... aurora s the aurora borealis and aurora australis . The artificial form of electriccurrent is the flow ... more details
List of current systems for electric rail traction 25 kV AC 60 Hz overhead 25 kV 60 ... 25 kV AC 60 Hz 60 Hz in some areas, see List of current systems for electric rail traction ... Japan, see List of current systems for electric rail traction 25 kV AC 50 Hz overhead 25 kV AC ... lines except Seoul subway Line 3 see List of current systems for electric rail traction 1500 V ... Metro Montreal Guide bars, see List of current systems for electric rail traction DC, four rail ... Paris Positive and sometimes negative polarity on guide bars, see List of current systems for electric ... Lyon Positive and sometimes negative polarity on guide bars, see List of current systems for electric ... Marseille Positive and sometimes negative polarity on guide bars, see List of current systems for electric ... Lille Positive and sometimes negative polarity on guide bars, see List of current systems for electric ... Rennes Positive and sometimes negative polarity on guide bars, see List of current systems for electric ... Railway electrification DEFAULTSORT List Of Current Systems For Electric Rail Traction Category ... to run three phase AC induction motors. Key to the tables below Volts voltage or volt Current DC direct current xx Hz frequency in hertz alternating current AC AC supplies are single phase electric power single phase , except where marked three phase electric power three phase Conductors overhead ... rowspan 8 flagicon Japan Japan Most tram lines Choshi Electric Railway Line Ch shi Electric Railway Ch shi, Chiba Eizan Electric Railway Kyoto, Kyoto Enoshima Electric Railway ... Line Wakayama Electric Railway Kishigawa Line Wakayama Prefecture Wakayama flagicon NLD ..., Ohio All three lines. San Diego Electric Railway & San Diego Trolley San Diego The San Diego Electric Railway is defunct, and is succeeded by the San Diego Trolley. San Francisco Municipal Railway ... Subway Daejeon Gwangju Subway Gwangju flagicon Slovakia Slovakia Tatra Electric Railway ... more details
Wiktionarypar currentCurrent may refer to Ongoing events Current affairs disambiguation The present Science and mathematics ElectriccurrentCurrent fluid , including Ocean current s Air current s Current stream currents in rivers and streams Current density , mathematical concept unifying electriccurrent, fluid current, and others The conserved current or Noether current in physics and mathematics Current mathematics , geometrical current in differential topology Business IBM Current , an early personal information management program Ships USS Current ARS 22 Media Current TV , a cable television network owned by Al Gore Current Project for Student Journalism , non profit organization dedicated to uniting and empowering students in the United States Current newspaper Current newspaper , American trade journal Current Publishing , American publishing company Currents periodical Currents periodical , an international trade law journal Currents TV series Currents TV series , Catholic news magazine television show in U.S. KCMP , a radio station known as The Current The Current song The Current song , a song by the Blue Man Group Current album Current album by Heatwave People Jeff Current , lead singer for Against All Will See also Currant disambiguation disambig ar cs Proud de Courant el es Corriente fr Courant gl Corrente he pl Current ru simple Current sk Pr d tr Ak m ... more details
The Current can refer to the following The Current Columbia University journal The Current journal , Columbia University s student journal of politics, culture and Jewish affairs. The Current newspaper The Current newspaper , the student newspaper of the University of Missouri St. Louis The Current NSU The Current newspaper , the student newspaper of the Nova Southeastern University The Current radio program , a current affairs radio program on CBC Radio One The Current song The Current song , a song by the Blue Man Group featuring Gavin Rossdale KCMP , a Minnesota Public Radio station known as The Current disambig ... more details
The Electric may refer to The Electric Blues Company , A backing band for former The Animals Animals keyboardist Alan Price Electric Slide , a four wall line dance Electric Cinema, Birmingham , the oldest running cinema in the UK disambig ... more details
Dark current is the constant response exhibited by a receptor of radiation during periods when it is not actively being exposed to light. It may refer to Dark current biochemistry The depolarizing Electriccurrentcurrent , carried by Sodium Na sup sup ions , that flows into a photoreceptor cell when unstimulated. Dark current physics The relatively small electriccurrent that flows through a photosensitive device when no photons are entering the device. Dark current chemistry The constant response produced by a spectroscopy spectrochemical receptor, in the absence of radiation. disambig Category Analytical chemistry Category Electrical engineering Category Electronic engineering Category Photoreceptor cells Category Optoelectronics de Dunkelstrom es Corriente de oscuridad ... more details
Constant current is a term most often used in electronics to describe a system that can vary the voltage across an electronic circuit to maintain a constant electriccurrent . When a component is indicated to be driven by a constant current, the driving circuit in essence is a current regulator and must appear to the component as a current source of suitable reliability. An important usage of constant current power supplies are LED s. While a high resistance series resistance is sufficient to light an LED sometimes the design needs to guard against high current. Another use is in fluorescent lamp s which have very dynamic electrical resistance and are optimally operated within a short range of currents. ref Caladen Circuit Corner, before Sep 5 2009, http caladan.nanosoft.ca c4 ccorner 4.php LED Current Controller ref See also Current source LED circuit References reflist Category Electriccurrent Category Electrical power control Category Electronics terms electronics stub ... more details
The limiting current , in electrochemistry, is the limiting value of a faradaic current that is approached as the rate of charge transfer to an electrode is increased . The limiting current can be approached, for example, by increasing the electric potential or decreasing the rate of mass transfer to the electrode. It is independent of the applied potential over a finite range, and is usually evaluated by subtracting the appropriate residual current from the measured total current. ref http www.iupac.org goldbook L03532.pdf ref A limiting current can have the character of an adsorption , catalytic , diffusion , or kinetic current, and may include a migration current. See also Butler Volmer equation References references chem stub Category Electrochemistry ru it Corrente limite ... more details
The faradaic current is the Electriccurrentcurrent generated by the redox reduction or oxidation of some chemical substance at an electrode . The net faradaic current is the algebraic sum of all the faradaic currents flowing through an indicator electrode or working electrode . ref GoldBookRef file F02321 title faradaic current ref References references chem stub Category Electrochemistry ... more details
Energy current is a flow of energy defined by the Poynting vector E H , as opposed to normal electriccurrentcurrent flow of charge physics charge . It was originally postulated by Oliver Heaviside . Explanation Energy current is a somewhat informal term that is used, on occasion, to describe the process of energy transfer in situations where the transfer can usefully be viewed in terms of a flow. It is particularly used when the transfer of energy is more significant to the discussion than the process by which the energy is transferred. For instance, the flow of fuel oil in a pipeline could be considered as an energy current, although this would not be a convenient way of visualising the fullness of the storage tanks. The units of energy current are those of power watt W . This is closely related to energy flux density, which is the rate of energy transfer per unit area measured in W m . Energy current in electromagnetism A specific use of the concept of energy current was promulgated by Oliver Heaviside in the last quarter of the 19th century. Building on the concept of the Poynting vector , which describes the flow of energy in a transverse electromagnetic wave as the vector product of its electric and magnetic fields E H , Heaviside sought to extend this by treating the transfer of energy due to the electriccurrent in a conductor in a similar manner. In doing so he reversed the normal view of current, so that the electric and magnetic fields due to the current are the prime ... current view presented a number of difficulties, most notably that in asserting that the energy flowed in the electric and magnetic fields around the conductor the theory is unable to explain ... electrons, the Drude model effectively deals with the traditional charge current and the Heaviside energy current views simultaneously. With this achievement of unification , the energy current approach ... charge current approach, which defines the concepts of current, voltage, resistance, etc, as commonly ... more details
electric charge above. DEFAULTSORT Conserved Current Category Electromagnetism Category Theoretical ...Unreferenced date December 2009 In physics a conserved current is a current, math j mu math , that satisfies the continuity equation math partial mu j mu 0 math . The continuity equation represents a conservation law, hence the name. Indeed, integrating the continuity equation over a volume math V math , large enough to have no currents through its surface, leads to the conservation law math partial over partial t Q 0 , math where math Q int V j 0dV math is the conserved quantity. In gauge theory gauge theories the gauge fields couple to conserved currents. For example, the electromagnetic field couples to the charge conservation conserved electriccurrent . Conserved quantities and symmetries Conserved current is the flow of the canonical conjugate of a quantity possessing a continuous function continuous translational symmetry . The continuity equation for the conserved current is a statement of a conservation law . Examples of canonical conjugate quantities are Time and energy the continuous ... function Phase waves phase and electric charge the continuous phase angle symmetry of the wave function implies the Electric charge Conservation of charge conservation of electric charge Conserved currents ... the existence of a conserved current to the existence of a symmetry of some quantity in the system under study. In practical terms, all conserved currents are Noether current s, as the existence of a conserved current implies the existence of a symmetry. Conserved currents play an important role in the theory of partial differential equation s, as the existence of a conserved current points to the existence ... forms the zeroth component of the four current 4 current . Conserved currents in electromagnetism ... rho partial t nabla cdot mathbf J 0 math where is the free electric charge density in units of C m J is the current density J math rho math v v is the velocity of the charges. The equation would ... more details
In condensed matter physics and electrochemistry , drift current is the electriccurrent , or movement of charge carrier s, which is due to the applied electric field , often stated as the electromotive force over a given distance.When an electric field is applied across a semiconductor material,the current ... by the electric field of the barrier potential. This current, which arises because of the motion of the drift of minority charge carriers, is the drift current in a p n junction diode. It flows in a direction opposite to the diffusion current which arises owing to the motion of the majority charge carriers across the junction. At equilibrium in an unbiased p n junction diode, the diffusion current, which flows from the p to n region, is exactly balanced by the equal and opposite drift current ... charge carriers can be thermally generated, drift current is temperature dependent. br When an electric ... with the electric field, whereas the negatively charged electrons move against the electric field. It is distinguished from diffusion current manifested via thermal and or density gradients , which results from the random Brownian motion of charge carriers independent of electrical stimulus. If an electric ... of electrons in a straight line is known as drift current. Drift current also depends on the mobility of charge carriers in the respective conducting medium. Drift current in a p n junction diode ... region, respectively. Due to the diffusion of the majority charge carriers across the junction, an electric ..., 9788126510894 pages 1115 ref In a biased p n junction, the drift current is independent of the biasing ... Electric Field intensity E Drift velocity V sub d sub mobility of the charge carriers Applied Electric field intensity. Holes move towards the negative terminal of the battery and electrons move ... constitutes a current known as drift current . Drift current due to the charge carriers such as free electrons and holes is the current passing through a square centimeter area perpendicular to the direction ... more details
. The current collector arms are electrical conductivity electrically conductive but mounted Electrical ... with the switch , transformer or Electric motor motor . The Rail profile steel rails of the Track rail transport tracks act as the Ground electricity electrical return . Electric vehicles that collect their current from overhead line system use different forms of one or two arm pantograph rail pantograph collectors , bow collector s, or trolley pole s. The current collection device presses ... . Contact shoe Electric railways with third rail s in tunnel s carry collector shoes projecting laterally ... and stud contact system s. A pair of contact shoes was used on Conduit current collection underground current collection systems . See also Ski collector References unreferenced date July 2008 commons Category Current collector Category Rail technologies ru uk ... more details
that allow current to flow only in one direction. Direct current may be made into alternating current with an inverter electrical inverter or a motor generator set. The first commercial electric power transmission developed by Thomas Edison in the late nineteenth century used direct current. Because of the significant advantages of alternating current over direct current in transforming and transmission, electric power distribution is nearly all alternating current today. In the mid 1950s, HVDC ... through a DC current source . The DC solution of an electric circuit is the solution where all voltages ... Category Electriccurrent Category Electric power Category American inventions ar bn ...Refimprove date June 2009 File Types of current by Zureks.svg thumb 250px Direct Current red curve . The horizontal axis measures time the vertical, current or voltage. Direct current DC is the unidirectional flow of electric charge . Direct current is produced by such sources as battery electrical batteries , thermocouple s, solar cell s, and commutator type electric machines of the dynamo type. Direct current may flow in a conductor material conductor such as a wire, but can also flow through semiconductor ... or ion beams . The electric charge flows in a constant direction, distinguishing it from alternating current AC . A archaism term formerly used for direct current was galvanic current . ref cite ... page 10 url http books.google.com books?id C2 9bcIjPBsC&pg PA10&dq 22galvanic current 22 22direct current 22 v onepage&q 22galvanic 20current 22 20 22direct 20current 22&f false ref File Current rectification diagram.svg right 250px thumb Types of direct current. Direct current may be obtained from an alternating current supply by use of a current switching arrangement called a rectifier ... current systems. For applications requiring direct current, such as third rail power systems, alternating current is distributed to a substation, which utilizes a rectifier to convert the power to direct ... more details
Unreferenced auto yes date December 2009 Image Planck current.png frame right 1 conductors, F sub p sub Planck force, l sub p sub Planck length, I sub p sub Planck current. The Planck current is the unit of electric current , denoted by I sub p sub , in the system of natural units known as Planck units . math I p q p t p c 6 4 pi varepsilon 0 G frac 1 2 math 3.479 × 10 sup 25 sup ampere A where math q p c hbar 4 pi varepsilon 0 frac 1 2 math is the Planck charge math t p hbar G c 5 frac 1 2 math is the Planck time math varepsilon 0 math permittivity in vacuum math hbar math is the reduced Planck constant G is the gravitational constant c is the speed of light in vacuum. The Planck current is that current which, in a conductor material conductor , carries a Planck charge in Planck time. Alternatively, the Planck current is that constant current which, if maintained in two straight parallel conductors of infinity infinite length and negligible circular cross section, and placed a Planck length apart in vacuum , would produce between these conductors a force equal to a Planck force per Planck length. Planckunits DEFAULTSORT Planck Current Category Natural units Current, planck Category Units of electric current Physics stub ar ca Corrent de Planck es Intensidad el ctrica de Planck eo Elektra kurento de Planck ko it Corrente di Planck pl Nat enie Plancka pt Corrente el trica de Planck ru sl Planckov tok fi Planckin s hk virta ... more details
flares ref Low, B. C. and Wolfson, R. 1988 Spontaneous formation of electriccurrent sheets and the origin ...Image Heliospheric current sheet.gif thumb 300px The heliospheric current sheet results from the influence ... ref http wso.stanford.edu gifs HCS.html Artist s Conception of the Heliospheric Current Sheet Wilcox Solar Observatory, Stanford University ref A current sheet is an electriccurrent that is confined to a surface, rather than being spread through a volume of space. Current sheets feature in magnetohydrodynamics MHD , the study of the behavior of electrically conductive fluids if there is an electriccurrent through part of the volume of such a fluid, magnetic forces tend to expel it from the fluid, compressing the current into thin layers that pass through the volume. The largest occurring current sheet in the Solar System is the so called Heliospheric current sheet , which is about 10,000 ... physics plasmas such as the sun solar corona , current sheets may have an aspect ratio breadth divided ... 1. Because current sheets are so thin in comparison to their size, they are often treated as if they have ... MHD . In reality, no current sheet may be infinitely thin because that would require infinitely fast motion of the charge carriers whose motion causes the current. Current sheets in plasmas store energy ... arise near strong current sheets, which are prone to collapse, causing magnetic reconnection and rapidly releasing the stored energy. ref Biskamp, Dieter May 1986 Magnetic reconnection via current sheets ... of magnetic confinement fusion , which requires strong electric currents in a hot plasma. Magnetic field of an infinite current sheet An infinite current sheet can be modelled as an infinite number of parallel wires all carrying the same current. Assuming each wire carries current I , and there are N ... R is a rectangular loop surrounding the current sheet. In the two sides perpendicular to the sheet, math ... math Solving for B , plugging in for I sub enc sub total current enclosed in path R as I N L , and simplifying ... more details
Expert subject Physics date May 2009 Unreferenced date May 2009 Introduction Diffusion current is a electriccurrentcurrent in a semiconductor caused by the diffusion of charge carriers holes and or electrons . Diffusion current can be in the same or opposite direction of a drift current , that is formed due to the electric field in the semiconductor. At equilibrium in a p n junction , the forward diffusion current in the depletion region is balanced with a reverse drift current, so that the net current is zero. The diffusion constant for a doped material can be determined with the Haynes Shockley experiment . Diffusion current versus drift current class wikitable Diffusion current Drift current Diffusion current occurs even though there isn t an electric field applied to the semiconductor . Drift current depends on the electric field applied on the p n junction diode. It depends on constants .... It depends upon permittivity. Direction of the diffusion current depends on the change in the carrier concentrations, not the concentrations themselves. Direction of the drift current depends on the polarity of the applied field. Carrier Actions of Diffusion Current No external electric field across the semiconductor is required for the diffusion of current to take place. This is because diffusion ... there is a flow of current. This flow of current is called the diffusion current. The drift current and the diffusion current make up the total current in the conductor. The change in the concentration of the carrier particles develops a gradient. Due to this gradient an electric field is produced in the semiconductor. Derivation of diffusion current To derive the diffusion current in semi ... with the net current equation in a semi conductor diode , big J sub n sub q sub n sub E D sub ... big Since, sub i sub V sub a sub V sub t sub . We obtain the equation of current caused due to diffusion ... 1 big .....Equation 5 From equation 5 we can observe that the current depends exponentially on the input ... more details
About an atmospheric effect the effect in nuclear magnetic resonance Chemical shift Factors causing chemical shifts A ring current is an electric current carried by charged particles trapped in a planet s magnetosphere . It is caused by the longitudinal drift of energetic 10&ndash 200 k electron volt eV particles. Earth s ring current File Currents.jpg thumb right 300px Schematic view of the different current systems which shape the Earth s magnetosphere . Earth s ring current is responsible for shielding the lower latitudes of the Earth from magnetospheric electric fields. It therefore has a large effect on the electrodynamics of geomagnetic storm s. The ring current system consists of a band, at a distance of 3 to 5 Earth radius R sub E sub , ref cite book title Introduction to Geomagnetically Trapped Radiation author Martin Walt year 1994 ref which lies in the celestial sphere equatorial plane and circulates clockwise around the Earth when viewed from the north . The particles of this region produce a magnetic field in opposition to the Earth s magnetic field and so an Earthly observer would observe a decrease in the magnetic field in this area. The ring current energy is mainly carried around by the ions, most of which are protons. However, one also sees alpha particles in the ring current, a type of ion that is plentiful in the solar wind. In addition, a certain percentage are O sup sup oxygen ions, similar to those in the ionosphere of Earth, though much more energetic. This mixture of ions suggests that ring current particles probably come from more than one source. The ring current and geomagnetic storms During a geomagnetic storm , the number of particles in the ring current will increase. As a result there is a decrease in the effects of Earth s magnetic field geomagnetic field . See also Van Allen radiation belt Magnetosphere References references cite journal doi 10.1023 B SPAC.0000007516.10433.ad title Ring Current Energy Input and Decay journal Space S ... more details
Unreferenced stub auto yes date December 2009 The Charged current interaction is one of the ways in which subatomic particles can interact by means of the weak force . It is mediated by the W and Z bosons SubatomicParticle W boson and SubatomicParticle W boson bosons . The interaction is often incorrectly believed to be called charged because the W bosons have electric charge . However, the charged current that gives the interaction its name is that of the interacting particles. For example, the charged current contribution to the SubatomicParticle Electron neutrino SubatomicParticle Electron SubatomicParticle Electron neutrino SubatomicParticle Electron elastic scattering amplitude math mathfrak M mathrm CC propto J mu mathrm CC mathrm e to nu mathrm e J mathrm CC mu nu mathrm e to mathrm e math where the charged currents describing the flow of one fermion into the other are given by math J mathrm CC mu f to f bar u f gamma mu frac 1 2 left 1 gamma 5 right u f . math See also Neutral current DEFAULTSORT Charged Current Category Electroweak theory Particle stub ar ru uk ... more details
article date April 2010 In electrical engineering , a current transformer CT is used for measurement of electric currents. Current transformers, together with voltage transformers VT potential transformers PT , are known as instrument transformers . When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective ... Image SF6 current transformer TGFM 110 Russia.jpg 160 px thumb SF sub 6 sub 110 kV current transformer TGFM series, Russia Image CurrentTransformers.jpg right thumb 300px Current transformers used in electricity ... , a current transformer has a primary winding, a magnetic core , and a secondary winding. The alternating current flowing in the primary produces a magnetic field in the core, which then induces a current in the secondary winding circuit. A primary objective of current transformer design is to ensure that the primary and secondary circuits are efficiently coupled, so that the secondary current bears an accurate relationship to the primary current. The most common design of CT consists ... tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry current through the magnetic core. Window type current transformers ... user or switchgear manufacturer. Typical examples of low voltage single ratio metering current transformers are either ring type or plastic moulded case. High voltage current transformers are mounted ... secondary current is commonly standardized at 1 or 5 amperes. For example, a 4000 5 CT would provide an output current of 5 amperes when the primary was passing 4000 amperes. The secondary ... more details
current is a quantity that is defined in terms of the rate of change of electric displacement field . Displacement current has the units of electriccurrent density , and it has an associated magnetic field just as actual currents do. However it is not an electriccurrent of moving Electric charge charges , but a time varying electric field . In materials, there is also a contribution from the slight ... November 2011 in connection with the displacement of electric particles in a dielectric medium. Maxwell added displacement current to the electriccurrent term in Amp re s circuital law Amp re s Circuital ..., charging the capacitor and increasing the electric field between its plates. The same current enters ... current Capacitance br DEFAULTSORT Displacement Current Category Electriccurrent Category Electrodynamics ... electricity, magnetism and optics into one single unified theory. The displacement current ... many phenomena, most particularly the existence of electromagnetic wave s. Explanation The electric ... sub 0 sub is the permittivity of free space E is the electric field intensity P is the polarization ... defines the displacement current , which therefore has two components in a dielectric ref name Jackson ... of charge, but it does have an associated magnetic field, just as does a current due to charge motion. Some authors apply the name displacement current to only this contribution. ref name Griffiths ... ref The second term on the right hand side is associated with the electric polarization polarization ... move a little under the influence of an applied electric field . The positive and negative ... of polarization corresponds to charge movement and so is equivalent to a current. This polarization is the displacement current as it was originally conceived by Maxwell. Maxwell made no special treatment ... justification of displacement current is explained below. Isotropic dielectric case In the case of a very ... of the dielectric and sub 0 sub is the electric constant . In this equation the use of , accounts ... more details
dablink This page is about the electriccurrent density in electromagnetism . For the probability current density in quantum mechanics, see Probability current . Current density is a measure of the density of flow of a conserved charge physics charge . Usually the charge is the electric charge, in which case the associated current density is the electriccurrent per unit area of cross section, but the term current density can also be applied to other conserved quantities. It is defined as a vector geometric vector whose magnitude is the current per cross sectional area. In SI unit s, the electriccurrent density is measured in ampere s per square metre . Definition Electriccurrent is a coarse, average quantity that tells what is happening in an entire wire. The distribution of flow of electric charge charge is described by the current density math mathbf J mathbf r , t qn mathbf r ,t mathbf v d mathbf r ,t rho mathbf r ,t mathbf v d mathbf r ,t , , math where J r ,&thinsp t is the current ... to the current density assumes the current simply is proportional to the electric field, as expressed ... average drift velocity at position r at time t SI unit metre s per second Importance Current density ... strongly upon the designed current level, and the current density then is determined by the dimensions ... the lower current demanded by smaller semiconductor devices devices , there is trend toward higher current densities to achieve higher device numbers in ever smaller semiconductor chip chip areas. See Moore s law . At high frequencies, current density can increase because the conducting region in a wire becomes confined near its surface, the so called skin effect . High current densities have undesirable ... , making them dissipate Power physics power in the form of heat. The current density must be kept ... failing. At high current densities the material forming the interconnections actually moves, a phenomenon called electromigration . In superconductivity superconductors excessive current density may ... more details
currentelectric motor s and transformer s may draw several times their normal full load current ...Image Inrush current.gif frame right An example of inrush current transients during capacitor bank energization. The peak inrush current transient rises as high as 28.4 kA Inrush current , input surge current or switch on surge refers to the maximum, instantaneous input current electricity current drawn ... inrush currents relative to their steady state currents. This is typically the charging current ... the circuit when the usually harmless inrush current flows. Transformers When a transformer is first energized a transient current up to 10 to 50 times larger than the rated transformer current can ... of the primary voltage. For large transformers, inrush current can last for several seconds. Toroid ... line are limiting the current. File Rktr Inrush 100Va.png thumb right An example of inrush current ... current. Protection Unreferenced section date January 2008 A resistor in series with the line can be used to limit the current charging input capacitors. However, this approach is not very efficient ... power. Inrush current can also be reduced by inrush current limiter s. Negative temperature coefficient ... to prevent damage caused by inrush current. A thermistor is a thermally sensitive resistor with a resistance ... NTC thermistors at Temperatures.com ref . As the inrush current limiter self heats, the current ... current flow charges the input capacitors. After the capacitors in the power supply become charged, the self heated inrush current limiter offers little resistance in the circuit, with a low voltage drop ... the inrush current unless it cools for more than 1 minute to get a higher resistance. Another disadvantage ... current is a transformer switching relay . This does not need time for cool down. It can deal ... circuit. The circuit would support a current limited precharge mode during the charging of capacitors ... of full charge. References reflist http www.ametherm.com Inrush Current inrush current faq.html Inrush ... more details
No footnotes date April 2009 File Types of current by Zureks.svg thumb Alternating Current green curve . The horizontal axis measures time the vertical, current or voltage. In alternating current AC , also ac , the movement of electric charge periodically reverses direction. In direct current DC, also dc , the flow of electric charge is only in one direction. The abbreviations AC and DC are often used to mean simply alternating and direct , as when they modify Electriccurrentcurrent or voltage ... mains power systems found in the world. Modern HVDC high voltage, direct currentelectric ... for reducing radiation loss As written above, an alternating current is made of electric ... by means of an electriccurrent , but rather by means of a guided electromagnetic field . Although .... DEFAULTSORT Alternating Current Category Electrical engineering Category Electriccurrent ... Electric Light Association publisher Trow Press year 1915 page 81 url http books.google.com books?id ZEpWAAAAMAAJ&pg PA81 ref AC is the form in which electric power is delivered to businesses and residences ... frequency radio signals carried on electrical wires are also examples of alternating current ... current is by Guillaume Duchenne , inventor and developer of electrotherapy . In 1855, he announced that AC was superior to direct current for electrotherapeutic triggering of muscle contractions. ref ... the interest of Westinghouse Electric 1886 Westinghouse . They also exhibited the invention in Turin in 1884, where it was adopted for an electric lighting system. Many of their designs were adapted ... electrical devices. Ferranti believed in the success of alternating current power distribution early on, and was one of the few experts in this system in the UK. In 1887 the London Electric Supply Corporation ... still have electric meters with the Ferranti AC patent stamped on them. William Stanley, Jr. designed ... contributed subsequently to this field. AC systems overcame the limitations of the direct current system ... more details
Current limiting is the practice in electrical or electronics electronic Electronic circuit circuit s of imposing an upper limit on the electriccurrentcurrent that may be delivered to a External electric load load with the purpose of protecting the circuit generating or transmitting the current from ... the peak current in a circuit, by opening and clearing the fault in a sub cycle time frame. Mains power The simplest form of current limiting for mains is a Fuse electrical fuse . As the current ... current limiting. Compared to circuit breakers, fuses attain faster current limitation by means of arc ... is the single operation principle once blown, they need to be replaced or reset. Inrush current limiting Main Inrush current limiter An inrush current limiter is a device or group of devices used to limit inrush current. Negative temperature coefficient NTC thermistors and resistors are two of the simplest ... power circuits Cleanup remainder date February 2011 Image Current limiting using bjt.gif thumb right 200px Active current limiting or short circuit protection Electronic circuits like regulated DC power supplies and power amplifiers employ, in addition to fuses, active current limiting since a fuse alone may not be able to protect the internal devices of the circuit in an over current or short ... sub is the load current sensing device. Q2 is the protection transistor which turns on as soon as the voltage ... sens sub and the load current through it I sub load sub . When Q2 turns on, it removes base current from Q1 thereby reducing the collector current of Q1. Neglecting the base currents of Q1 and Q2, the collector current of Q1 is also the load current. Thus, R sub sens sub fixes the maximum current ..., if R sub sens sub 0.33 , the current is limited to about 2 A even if R sub load sub becomes a short ... current limited only by R sub sens sub , and dependent on the output voltage V sub o sub if R sub load ... the dissipation will be much greater enough to destroy Q1 . With Q2 in place, the current is limited ... more details
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