83-518: The Trossingen Railway ( Trossinger Eisenbahn , TE ) is a DC -electrified branch line in the German state of Baden-Württemberg . The branch line has connected the town of Trossingen with Trossingen station , which is located on its periphery, since 1897. Trossingen station (formerly called Trossingen Staatsbahnhof —"state station") is on the Rottweil–Villingen railway . The railway is not part of
166-430: A galvanometer , but this method involves breaking the electrical circuit , which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices, at the circuit level, use various techniques to measure current: Joule heating, also known as ohmic heating and resistive heating , is the process of power dissipation by which
249-510: A rectifier , which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter . Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes. It
332-453: A rectifier . Direct current may flow in a conductor such as a wire, but can also flow through semiconductors , insulators , or even through a vacuum as in electron or ion beams . An old name for direct current was galvanic current . Natural observable examples of electric current include lightning , static electric discharge , and the solar wind , the source of the polar auroras . Man-made occurrences of electric current include
415-438: A vacuum as in electron or ion beams . The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current . The abbreviations AC and DC are often used to mean simply alternating and direct , as when they modify current or voltage . Direct current may be converted from an alternating current supply by use of
498-537: A DC circuit. However, most such circuits have a DC solution. This solution gives the circuit voltages and currents when the circuit is in DC steady state . Such a circuit is represented by a system of differential equations . The solution to these equations usually contain a time varying or transient part as well as constant or steady state part. It is this steady state part that is the DC solution. There are some circuits that do not have
581-407: A DC solution. Two simple examples are a constant current source connected to a capacitor and a constant voltage source connected to an inductor. In electronics, it is common to refer to a circuit that is powered by a DC voltage source such as a battery or the output of a DC power supply as a DC circuit even though what is meant is that the circuit is DC powered. In a DC circuit, a power source (e.g.
664-450: A battery system to ensure power is maintained for subscriber lines during power interruptions. Other devices may be powered from the telecommunications DC system using a DC-DC converter to provide any convenient voltage. Many telephones connect to a twisted pair of wires, and use a bias tee to internally separate the AC component of the voltage between the two wires (the audio signal) from
747-423: A battery, capacitor, etc.) has a positive and negative terminal, and likewise, the load also has a positive and negative terminal. To complete the circuit, positive charges need to flow from the power source to the load. The charges will then return to the negative terminal of the load, which will then flow back to the negative terminal of the battery, completing the circuit. If either the positive or negative terminal
830-416: A catalyst to produce electricity and water as byproducts) also produce only DC. Light aircraft electrical systems are typically 12 V or 24 V DC similar to automobiles. Electric current An electric current is a flow of charged particles , such as electrons or ions , moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through
913-411: A circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of charge carriers . Negatively charged carriers, such as the electrons (the charge carriers in metal wires and many other electronic circuit components), therefore flow in
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#1732876744162996-405: A common lead-acid electrochemical cell, electric currents are composed of positive hydronium ions flowing in one direction, and negative sulfate ions flowing in the other. Electric currents in sparks or plasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, the electric current is entirely composed of flowing ions. In a metal , some of
1079-416: A definition of current independent of the type of charge carriers, conventional current is defined as moving in the same direction as the positive charge flow. So, in metals where the charge carriers (electrons) are negative, conventional current is in the opposite direction to the overall electron movement. In conductors where the charge carriers are positive, conventional current is in the same direction as
1162-524: A direct current source . The DC solution of an electric circuit is the solution where all voltages and currents are constant. Any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero-mean time-varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time. Although DC stands for "direct current", DC often refers to "constant polarity". Under this definition, DC voltages can vary in time, as seen in
1245-447: A localized high current. These regions may be initiated by field electron emission , but are then sustained by localized thermionic emission once a vacuum arc forms. These small electron-emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field. Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conductivity. Superconductivity
1328-428: A metal wire is connected across the two terminals of a DC voltage source such as a battery , the source places an electric field across the conductor. The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electrons are therefore the charge carrier in a typical solid conductor. For a steady flow of charge through
1411-404: A millimetre per second. To take a different example, in the near-vacuum inside a cathode-ray tube , the electrons travel in near-straight lines at about a tenth of the speed of light . Any accelerating electric charge, and therefore any changing electric current, gives rise to an electromagnetic wave that propagates at very high speed outside the surface of the conductor. This speed is usually
1494-408: A particular band called the valence band . Semiconductors and insulators are distinguished from metals because the valence band in any given metal is nearly filled with electrons under usual operating conditions, while very few (semiconductor) or virtually none (insulator) of them are available in the conduction band , the band immediately above the valence band. The ease of exciting electrons in
1577-472: A significant fraction of the speed of light, as can be deduced from Maxwell's equations , and is therefore many times faster than the drift velocity of the electrons. For example, in AC power lines , the waves of electromagnetic energy propagate through the space between the wires, moving from a source to a distant load , even though the electrons in the wires only move back and forth over a tiny distance. The ratio of
1660-405: A surface, the current I (in amperes) can be calculated with the following equation: I = Q t , {\displaystyle I={Q \over t}\,,} where Q is the electric charge transferred through the surface over a time t . If Q and t are measured in coulombs and seconds respectively, I is in amperes. More generally, electric current can be represented as
1743-412: A surface. The moving particles are called charge carriers , which may be one of several types of particles, depending on the conductor . In electric circuits the charge carriers are often electrons moving through a wire . In semiconductors they can be electrons or holes . In an electrolyte the charge carriers are ions , while in plasma , an ionized gas, they are ions and electrons. In
SECTION 20
#17328767441621826-599: Is I , which originates from the French phrase intensité du courant , (current intensity). Current intensity is often referred to simply as current . The I symbol was used by André-Marie Ampère , after whom the unit of electric current is named, in formulating Ampère's force law (1820). The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using C to I until 1896. The conventional direction of current, also known as conventional current ,
1909-514: Is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature . It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden . Like ferromagnetism and atomic spectral lines , superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect ,
1992-554: Is also used for some railways , especially in urban areas . High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids. Direct current was produced in 1800 by Italian physicist Alessandro Volta 's battery, his Voltaic pile . The nature of how current flowed was not yet understood. French physicist André-Marie Ampère conjectured that current travelled in one direction from positive to negative. When French instrument maker Hippolyte Pixii built
2075-482: Is an AC device which uses a rectifier to produce DC for battery charging. Most highway passenger vehicles use nominally 12 V systems. Many heavy trucks, farm equipment, or earth moving equipment with Diesel engines use 24 volt systems. In some older vehicles, 6 V was used, such as in the original classic Volkswagen Beetle . At one point a 42 V electrical system was considered for automobiles, but this found little use. To save weight and wire, often
2158-411: Is arbitrarily defined as the direction in which positive charges flow. In a conductive material , the moving charged particles that constitute the electric current are called charge carriers . In metals, which make up the wires and other conductors in most electrical circuits , the positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively charged electrons are
2241-435: Is commonly found in many extra-low voltage applications and some low-voltage applications, especially where these are powered by batteries or solar power systems (since both can produce only DC). Most electronic circuits or devices require a DC power supply . Domestic DC installations usually have different types of sockets , connectors , switches , and fixtures from those suitable for alternating current. This
2324-683: Is current. Magnetic fields can also be used to make electric currents. When a changing magnetic field is applied to a conductor, an electromotive force (EMF) is induced, which starts an electric current, when there is a suitable path. When an electric current flows in a suitably shaped conductor at radio frequencies , radio waves can be generated. These travel at the speed of light and can cause electric currents in distant conductors. In metallic solids, electric charge flows by means of electrons , from lower to higher electrical potential . In other media, any stream of charged objects (ions, for example) may constitute an electric current. To provide
2407-427: Is disconnected, the circuit will not be complete and the charges will not flow. In some DC circuit applications, polarity does not matter, which means you can connect positive and negative backwards and the circuit will still be complete and the load will still function normally. However, in most DC applications, polarity does matter, and connecting the circuit backwards will result in the load not working properly. DC
2490-412: Is distributed to a substation, which utilizes a rectifier to convert the power to direct current. The term DC is used to refer to power systems that use only one electrical polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current. For example, the voltage across a DC voltage source is constant as is the current through
2573-423: Is in a nanowire , for every energy there is a state with electrons flowing in one direction and another state with the electrons flowing in the other. For a net current to flow, more states for one direction than for the other direction must be occupied. For this to occur, energy is required, as in the semiconductor the next higher states lie above the band gap. Often this is stated as: full bands do not contribute to
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2656-468: Is low, gases are dielectrics or insulators . However, once the applied electric field approaches the breakdown value, free electrons become sufficiently accelerated by the electric field to create additional free electrons by colliding, and ionizing , neutral gas atoms or molecules in a process called avalanche breakdown . The breakdown process forms a plasma that contains enough mobile electrons and positive ions to make it an electrical conductor. In
2739-447: Is mostly due to the lower voltages used, resulting in higher currents to produce the same amount of power . It is usually important with a DC appliance to observe polarity, unless the device has a diode bridge to correct for this. Most automotive applications use DC. An automotive battery provides power for engine starting, lighting, the ignition system, the climate controls, and the infotainment system among others. The alternator
2822-455: Is opposite that of the chosen reference direction. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance , one arrives at the usual mathematical equation that describes this relationship: I = V R , {\displaystyle I={\frac {V}{R}},} where I
2905-655: Is opposite to the velocity of the charges. In SI units , current density (symbol: j) is expressed in the SI base units of amperes per square metre. In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform. In such conditions, Ohm's law states that the current is directly proportional to the potential difference between two ends (across) of that metal (ideal) resistor (or other ohmic device ): I = V R , {\displaystyle I={V \over R}\,,} where I {\displaystyle I}
2988-433: Is the current through the conductor in units of amperes , V is the potential difference measured across the conductor in units of volts , and R is the resistance of the conductor in units of ohms . More specifically, Ohm's law states that the R in this relation is constant, independent of the current. In alternating current (AC) systems, the movement of electric charge periodically reverses direction. AC
3071-400: Is the current, measured in amperes; V {\displaystyle V} is the potential difference , measured in volts ; and R {\displaystyle R} is the resistance , measured in ohms . For alternating currents , especially at higher frequencies, skin effect causes the current to spread unevenly across the conductor cross-section, with higher density near
3154-441: Is the form of electric power most commonly delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave , though certain applications use alternative waveforms, such as triangular or square waves . Audio and radio signals carried on electrical wires are also examples of alternating current. An important goal in these applications is recovery of information encoded (or modulated ) onto
3237-456: Is the rate at which charge passes through a chosen unit area. It is defined as a vector whose magnitude is the current per unit cross-sectional area. As discussed in Reference direction , the direction is arbitrary. Conventionally, if the moving charges are positive, then the current density has the same sign as the velocity of the charges. For negative charges, the sign of the current density
3320-403: Is zero net current within the metal. At room temperature, the average speed of these random motions is 10 metres per second. Given a surface through which a metal wire passes, electrons move in both directions across the surface at an equal rate. As George Gamow wrote in his popular science book, One, Two, Three...Infinity (1947), "The metallic substances differ from all other materials by
3403-626: The Deutsche Bahn network; instead it is owned by Stadtwerke Trossingen GmbH . This company formerly operated the railway, but since 2003, operations have been carried out by the Hohenzollerische Landesbahn (HzL). Freight operations were abandoned in 1996. When the Royal Württemberg State Railways ( Königlich Württembergischen Staats-Eisenbahnen ) opened the Rottweil–Villingen railway on 26 August 1869, Trossingen
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3486-849: The International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ). Electric current is also known as amperage and is measured using a device called an ammeter . Electric currents create magnetic fields , which are used in motors, generators, inductors , and transformers . In ordinary conductors, they cause Joule heating , which creates light in incandescent light bulbs . Time-varying currents emit electromagnetic waves , which are used in telecommunications to broadcast information. The conventional symbol for current
3569-405: The electrical conductivity . However, as a semiconductor's temperature rises above absolute zero , there is more energy in the semiconductor to spend on lattice vibration and on exciting electrons into the conduction band. The current-carrying electrons in the conduction band are known as free electrons , though they are often simply called electrons if that is clear in context. Current density
3652-458: The reference direction of the current I {\displaystyle I} . When analyzing electrical circuits , the actual direction of current through a specific circuit element is usually unknown until the analysis is completed. Consequently, the reference directions of currents are often assigned arbitrarily. When the circuit is solved, a negative value for the current implies the actual direction of current through that circuit element
3735-418: The watt (symbol: W), is equivalent to one joule per second. In an electromagnet a coil of wires behaves like a magnet when an electric current flows through it. When the current is switched off, the coil loses its magnetism immediately. Electric current produces a magnetic field . The magnetic field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as there
3818-747: The 1990s, the line has been considered in danger of being closed, but instead it was saved by being integrating into the Ringzug concept of the Schwarzwald-Baar-Heuberg planning region. Consequently, diesel-powered Regio-Shuttle railcars, operated by the HzL, took over the operation of all traffic on the Trossingen Railway in 2003. Some of the services run via Villingen-Schwenningen and Donaueschingen to Bräunlingen . The catenary has not been needed in scheduled operations since Friday, 11 July 2003 and
3901-401: The AC signal. In contrast, direct current (DC) refers to a system in which the movement of electric charge in only one direction (sometimes called unidirectional flow). Direct current is produced by sources such as batteries , thermocouples , solar cells , and commutator -type electric machines of the dynamo type. Alternating current can also be converted to direct current through use of
3984-448: The DC component of the voltage between the two wires (used to power the phone). High-voltage direct current (HVDC) electric power transmission systems use DC for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. Applications using fuel cells (mixing hydrogen and oxygen together with
4067-412: The charge carriers, free to move about in the metal. In other materials, notably the semiconductors , the charge carriers can be positive or negative, depending on the dopant used. Positive and negative charge carriers may even be present at the same time, as happens in an electrolyte in an electrochemical cell . A flow of positive charges gives the same electric current, and has the same effect in
4150-402: The charge carriers. In a vacuum , a beam of ions or electrons may be formed. In other conductive materials, the electric current is due to the flow of both positively and negatively charged particles at the same time. In still others, the current is entirely due to positive charge flow . For example, the electric currents in electrolytes are flows of positively and negatively charged ions. In
4233-407: The circuit voltages and currents are independent of time. A particular circuit voltage or current does not depend on the past value of any circuit voltage or current. This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time. If a capacitor or inductor is added to a DC circuit, the resulting circuit is not, strictly speaking,
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#17328767441624316-529: The complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics . In a semiconductor it is sometimes useful to think of the current as due to the flow of positive " holes " (the mobile positive charge carriers that are places where
4399-544: The correct voltages within radio antennas , radio waves are generated. In electronics , other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube , the flow of ions inside a battery , and the flow of holes within metals and semiconductors . A biological example of current is the flow of ions in neurons and nerves, responsible for both thought and sensory perception. Current can be measured using an ammeter . Electric current can be directly measured with
4482-668: The electrical infrastructure is now only used in museum operations. However, two vintage railcars were temporarily restored to scheduled operations from December 2004 because the Ringzug was short of rolling stock. The Trossingen Stadt terminus now has only one platform track for passenger traffic. The remaining three tracks are used for the railway museum. In addition to connecting services to trains in Trossingen Station, some Ringzug services also run directly to Villingen and Bräunlingen. In Trossingen Stadt station there are connections to
4565-410: The energy of the ground state, the state in which electrons are tightly bound to the atomic nuclei of the material, and the free electron energy, the latter describing the energy required for an electron to escape entirely from the material. The energy bands each correspond to many discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are occupied, up to
4648-458: The fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current." When
4731-654: The first dynamo electric generator in 1832, he found that as the magnet used passed the loops of wire each half turn, it caused the flow of electricity to reverse, generating an alternating current . At Ampère's suggestion, Pixii later added a commutator , a type of "switch" where contacts on the shaft work with "brush" contacts to produce direct current. The late 1870s and early 1880s saw electricity starting to be generated at power stations . These were initially set up to power arc lighting (a popular type of street lighting) running on very high voltage (usually higher than 3,000 volts) direct current or alternating current. This
4814-459: The flow of conduction electrons in metal wires such as the overhead power lines that deliver electrical energy across long distances and the smaller wires within electrical and electronic equipment. Eddy currents are electric currents that occur in conductors exposed to changing magnetic fields. Similarly, electric currents occur, particularly in the surface, of conductors exposed to electromagnetic waves . When oscillating electric currents flow at
4897-643: The following bus routes (as of 2014): A small museum of items from the Trossinger Railway has been located in the roundhouse at Trossingen Stadt station since 5 June 2005. Most of the historic rolling stock have been housed here. The Freundeskreis der Trossinger Eisenbahn (Friends of the Trossinger Railway) is involved in the Museum. This was established on 7 September 2004 and its first official excursion trip ran on 1 May 2005. The T1 railcars are said to be
4980-410: The heavier positive ions, and hence carry the bulk of the current. The free ions recombine to create new chemical compounds (for example, breaking atmospheric oxygen into single oxygen [O 2 → 2O], which then recombine creating ozone [O 3 ]). Since a " perfect vacuum " contains no charged particles, it normally behaves as a perfect insulator. However, metal electrode surfaces can cause a region of
5063-440: The length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the wire. P ∝ I 2 R . {\displaystyle P\propto I^{2}R.} This relationship is known as Joule's Law . The SI unit of energy was subsequently named the joule and given the symbol J . The commonly known SI unit of power,
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#17328767441625146-512: The metal frame of the vehicle is connected to one pole of the battery and used as the return conductor in a circuit. Often the negative pole is the chassis "ground" connection, but positive ground may be used in some wheeled or marine vehicles. In a battery electric vehicle , there are usually two separate DC systems. The "low voltage" DC system typically operates at 12V, and serves the same purpose as in an internal combustion engine vehicle. The "high voltage" system operates at 300-400V (depending on
5229-424: The metal into the vacuum. Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes . Cold electrodes can also spontaneously produce electron clouds via thermionic emission when small incandescent regions (called cathode spots or anode spots ) are formed. These are incandescent regions of the electrode surface that are created by
5312-424: The moving electrons in metals. In certain electrolyte mixtures, brightly coloured ions are the moving electric charges. The slow progress of the colour makes the current visible. In air and other ordinary gases below the breakdown field, the dominant source of electrical conduction is via relatively few mobile ions produced by radioactive gases, ultraviolet light, or cosmic rays. Since the electrical conductivity
5395-400: The opposite direction of conventional current flow in an electrical circuit. A current in a wire or circuit element can flow in either of two directions. When defining a variable I {\displaystyle I} to represent the current, the direction representing positive current must be specified, usually by an arrow on the circuit schematic diagram . This is called
5478-403: The opposite direction of the electric field. The speed they drift at can be calculated from the equation: I = n A v Q , {\displaystyle I=nAvQ\,,} where Typically, electric charges in solids flow slowly. For example, in a copper wire of cross-section 0.5 mm , carrying a current of 5 A, the drift velocity of the electrons is on the order of
5561-502: The outer electrons in each atom are not bound to the individual molecules as they are in molecular solids , or in full bands as they are in insulating materials, but are free to move within the metal lattice . These conduction electrons can serve as charge carriers , carrying a current. Metals are particularly conductive because there are many of these free electrons. With no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there
5644-413: The passage of an electric current through a conductor increases the internal energy of the conductor, converting thermodynamic work into heat . The phenomenon was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current through the wire for a 30 minute period. By varying the current and
5727-468: The process, it forms a light emitting conductive path, such as a spark , arc or lightning . Plasma is the state of matter where some of the electrons in a gas are stripped or "ionized" from their molecules or atoms. A plasma can be formed by high temperature , or by application of a high electric or alternating magnetic field as noted above. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than
5810-401: The rate at which charge flows through a given surface as: I = d Q d t . {\displaystyle I={\frac {\mathrm {d} Q}{\mathrm {d} t}}\,.} Electric currents in electrolytes are flows of electrically charged particles ( ions ). For example, if an electric field is placed across a solution of Na and Cl (and conditions are right)
5893-428: The raw output of a rectifier or the fluctuating voice signal on a telephone line. Some forms of DC (such as that produced by a voltage regulator ) have almost no variations in voltage , but may still have variations in output power and current. A direct current circuit is an electrical circuit that consists of any combination of constant voltage sources, constant current sources, and resistors . In this case,
5976-596: The same time, the projected line was to be electrified. The relatively steep slope of the track—it climbed 66 metres towards the town—also favoured electric operations. The new railway was finally opened on 14 December 1898. It was taken over by the town of Trossingen in 1908 and it has been operated ever since as a municipal utility. The Trossinger Railway is unusual in that it does not use the 15 kV/16.7 Hz electrical system that eventually became normal in Germany. It also does not abut any other electrified railway lines. Since
6059-501: The semiconductor crystal is missing a valence electron). This is the case in a p-type semiconductor. A semiconductor has electrical conductivity intermediate in magnitude between that of a conductor and an insulator . This means a conductivity roughly in the range of 10 to 10 siemens per centimeter (S⋅cm ). In the classic crystalline semiconductors, electrons can have energies only within certain bands (i.e. ranges of levels of energy). Energetically, these bands are located between
6142-503: The semiconductor from the valence band to the conduction band depends on the band gap between the bands. The size of this energy band gap serves as an arbitrary dividing line (roughly 4 eV ) between semiconductors and insulators . With covalent bonds, an electron moves by hopping to a neighboring bond. The Pauli exclusion principle requires that the electron be lifted into the higher anti-bonding state of that bond. For delocalized states, for example in one dimension – that
6225-419: The sodium ions move towards the negative electrode (cathode), while the chloride ions move towards the positive electrode (anode). Reactions take place at both electrode surfaces, neutralizing each ion. Water-ice and certain solid electrolytes called proton conductors contain positive hydrogen ions (" protons ") that are mobile. In these materials, electric currents are composed of moving protons, as opposed to
6308-443: The surface, thus increasing the apparent resistance. The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas . (More accurately, a Fermi gas .) To create a net flow of charge, the particles must also move together with an average drift rate. Electrons are the charge carriers in most metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in
6391-529: The transport situation and when the state railway had shown no interest they ended up agreeing to establish a private company. To this end, the AG Elektrizitätswerk und Verbindungsbahn Trossingen (“Trossingen Electrical Works and Connecting Railway”) was established in 1896 and the appropriate license for the new line was issued on 31 December 1897. Because a power station was built nearby in Trossingen at
6474-405: The vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission . Thermionic emission occurs when the thermal energy exceeds the metal's work function , while field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunneling , which results in the ejection of free electrons from
6557-464: The vehicle), and provides the power for the traction motors . Increasing the voltage for the traction motors reduces the current flowing through them, increasing efficiency. Telephone exchange communication equipment uses standard −48 V DC power supply. The negative polarity is achieved by grounding the positive terminal of power supply system and the battery bank. This is done to prevent electrolysis depositions. Telephone installations have
6640-457: The world's oldest operational electric railway vehicles. 48°04′26″N 8°37′55″E / 48.0740°N 8.6319°E / 48.0740; 8.6319 Direct current Direct current ( DC ) is one-directional flow of electric charge . An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors , insulators , or even through
6723-406: Was followed by the widespread use of low voltage direct current for indoor electric lighting in business and homes after inventor Thomas Edison launched his incandescent bulb based electric " utility " in 1882. Because of the significant advantages of alternating current over direct current in using transformers to raise and lower voltages to allow much longer transmission distances, direct current
6806-403: Was not included in the route of the line. The new line ran about four kilometres in a straight line to the north of Trossingen. Despite the economic growth as a result of increasing industrialisation , in particular in the musical instrument industry (for instance Hohner ), Trossingen found itself increasingly isolated. Therefore, committed citizens of the town tried in subsequent years to improve
6889-477: Was replaced over the next few decades by alternating current in power delivery. In the mid-1950s, high-voltage direct current transmission was developed, and is now an option instead of long-distance high voltage alternating current systems. For long distance undersea cables (e.g. between countries, such as NorNed ), this DC option is the only technically feasible option. For applications requiring direct current, such as third rail power systems, alternating current
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