The volt (symbol: V) is the derived unit for electric potential, electric potential difference (voltage), and electromotive force.[1] It is named after the Italian physicist Alessandro Volta (1745–1827).

Josephson voltage standard chip developed by the National Bureau of Standards as a standard volt
General information
Unit systemSI derived unit
Unit ofElectric potential, electromotive force
Named afterAlessandro Volta
In SI base units:kg·m2·s−3·A−1


One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points.[2] It is also equal to the potential difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can be expressed in terms of SI base units (m, kg, s, and A) as

It can also be expressed as amperes times ohms (current times resistance, Ohm's law), watts per ampere (power per unit current, definition of electric power), or joules per coulomb (energy per unit charge), which is also equivalent to electronvolts per elementary charge:

Josephson junction definition

The "conventional" volt, V90, defined in 1988 by the 18th General Conference on Weights and Measures and in use from 1990, is implemented using the Josephson effect for exact frequency-to-voltage conversion, combined with the caesium frequency standard. For the Josephson constant, KJ = 2e/h (where e is the elementary charge and h is the Planck constant), the "conventional" value KJ-90 is used:

This standard is typically realized using a series-connected array of several thousand or tens of thousands of junctions, excited by microwave signals between 10 and 80 GHz (depending on the array design).[3] Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc., and no correction terms are required in a practical implementation.[4]

Water-flow analogy

In the water-flow analogy, sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage (difference in electric potential) is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping and a capacitor/inductor could be likened to a "U" shaped pipe where a higher water level on one side could store energy temporarily.

The relationship between voltage and current is defined (in ohmic devices like resistors) by Ohm's law. Ohm's Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems.

Common voltages

Electronic multi meter
A multimeter can be used to measure the voltage between two positions.
1.5 V C-cell batteries

The voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. See Galvanic cell § Cell voltage. Cells can be combined in series for multiples of that voltage, or additional circuitry added to adjust the voltage to a different level. Mechanical generators can usually be constructed to any voltage in a range of feasibility.

Nominal voltages of familiar sources:


Alessandro Volta.jpeg
Alessandro Volta

In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani, Alessandro Volta developed the so-called voltaic pile, a forerunner of the battery, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc and silver. In 1861, Latimer Clark and Sir Charles Bright coined the name "volt" for the unit of resistance.[9] By 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad.[10] In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force.[11] They made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. They chose such a ratio because the cgs unit of voltage is inconveniently small and one volt in this definition is approximately the emf of a Daniell cell, the standard source of voltage in the telegraph systems of the day.[12] At that time, the volt was defined as the potential difference [i.e., what is nowadays called the "voltage (difference)"] across a conductor when a current of one ampere dissipates one watt of power.

PSM V85 D521 Group photograph of herman helmholtz and academic friends
Group photograph of Hermann Helmholtz, his wife (seated) and academic friends Hugo Kronecker (left), Thomas Corwin Mendenhall (right), Henry Villard (center) during the International Electrical Congress

The "international volt" was defined in 1893 as 1/1.434 of the emf of a Clark cell. This definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of "reproducible units" was abandoned in 1948.

Prior to the development of the Josephson junction voltage standard, the volt was maintained in national laboratories using specially constructed batteries called "standard cells". The United States used a design called the Weston cell from 1905 to 1972.

A proposed redefinition of SI base units, including defining the value of the elementary charge, is expected to take effect in 2019.[13]

See also


  1. ^ "SI Brochure, Table 3 (Section 2.2.2)". BIPM. 2006. Archived from the original on 2007-06-18. Retrieved 2007-07-29.
  2. ^ BIPM SI Brochure: Appendix 1, p. 144
  3. ^ Burroughs, Charles J.; Bent, Samuel P.; Harvey, Todd E.; Hamilton, Clark A. (1999-06-01), "1 Volt DC Programmable Josephson Voltage Standard", IEEE Transactions on Applied Superconductivity, Institute of Electrical and Electronics Engineers (IEEE), 9 (3): 4145–4149, Bibcode:1999ITAS....9.4145B, doi:10.1109/77.783938, ISSN 1051-8223, retrieved 2014-06-27
  4. ^ Keller, Mark W (2008-01-18), "Current status of the quantum metrology triangle" (PDF), Metrologia, 45 (1): 102–109, Bibcode:2008Metro..45..102K, doi:10.1088/0026-1394/45/1/014, ISSN 0026-1394, archived from the original (PDF) on 2010-05-27, retrieved 2010-04-11, Theoretically, there are no current predictions for any correction terms. Empirically, several experiments have shown that KJ and RK are independent of device design, material, measurement setup, etc. This demonstration of universality is consistent with the exactness of the relations, but does not prove it outright.
  5. ^ Bullock, Orkand, and Grinnell, pp. 150–151; Junge, pp. 89–90; Schmidt-Nielsen, p. 484
  6. ^ Hill, Paul Horowitz; Winfield; Winfield, Hill (2015). The Art of Electronics (3. ed.). Cambridge [u.a.]: Cambridge Univ. Press. p. 689. ISBN 978-0-521-809269.
  7. ^ SK Loo and Keith Keller (Aug 2004). "Single-cell Battery Discharge Characteristics Using the TPS61070 Boost Converter" (PDF). Texas Instruments.
  8. ^ 2012-2013 Model S Emergency Response Guide (PDF), retrieved 2017-08-06
  9. ^ As names for units of various electrical quantities, Bright and Clark suggested "ohma" for voltage, "farad" for charge, "galvat" for current, and "volt" for resistance. See:
  10. ^ Sir W. Thomson, et al. (1873) "First report of the Committee for the Selection and Nomenclature of Dynamical and Electrical Units," Report of the 43rd Meeting of the British Association for the Advancement of Science (Bradford, September 1873), pp. 222-225. From p. 223: "The "ohm," as represented by the original standard coil, is approximately 109 C.G.S. units of resistance ; the "volt" is approximately 108 C.G.S. units of electromotive force ; and the "farad" is approximately 1/109 of the C.G.S. unit of capacity."
  11. ^ (Anon.) (September 24, 1881) "The Electrical Congress," The Electrician, 7 : 297.
  12. ^ Hamer, Walter J. (January 15, 1965). Standard Cells: Their Construction, Maintenance, and Characteristics (PDF). National Bureau of Standards Monograph #84. US National Bureau of Standards.
  13. ^ Draft Resolution A "On the revision of the International System of units (SI)" to be submitted to the CGPM at its 26th meeting (2018) (PDF)

External links

Automotive battery

An automotive battery is a rechargeable battery that supplies electrical current to a motor vehicle. Its main purpose is to feed the starter, which starts the engine. Once the engine is running, power for the car's electrical systems is supplied by the alternator.

Typically, starting discharges less than three percent of the battery capacity. For this reason, automotive batteries are designed to deliver maximum current for a short period of time. They are sometimes referred to as "SLI batteries" for this reason, for Starting, Lighting and Ignition. SLI batteries are not designed for deep discharging, and a full discharge can reduce the battery's lifespan.As well as starting the engine, an SLI battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes. While the engine is running, most of the power is provided by the alternator, which includes a voltage regulator to keep the output between 13.5 and 14.5 V.

Modern SLI batteries are lead-acid type, using six series-connected cells to provide a nominal 12 volt system (in most passenger vehicles and light trucks), or twelve cells for a 24 volt system in heavy trucks or earth-moving equipment, for example.Battery electric vehicles are powered by a high-voltage electric vehicle battery, but they usually have an automotive battery as well, so that they can use standard automotive accessories which are designed to run on 12 V.

Chevrolet Volt

The Chevrolet Volt is a plug-in hybrid car manufactured by General Motors, also marketed in rebadged variants as the Holden Volt in Australia and New Zealand, Buick Velite 5 in China, and with a different fascia as the Vauxhall Ampera in the United Kingdom and as the Opel Ampera in the remainder of Europe. In November 2018, GM announced it would cease Volt production in March 2019.Sales of the 2011 Volt began in the United States in mid-December 2010, followed by various European countries and other international markets in 2011. Global combined Volt/Ampera-family sales totaled about 177,000 units by the end of October 2018. The U.S. is the leading market, with 148,556 Volts delivered through October 2018, followed by Canada with 16,653 Volts sold through September 2018. Just over 10,000 Opel/Vauxhall Ampera cars had been sold in Europe as of June 2016, with the Netherlands leading the European region. As of September 2018, the Volt/Ampera family of vehicles is the world's all-time best-selling plug-in hybrid vehicle, and the Volt is also the U.S. all-time top-selling plug-in electric car.

The Volt operates as a pure battery electric vehicle until its battery capacity drops to a predetermined threshold from full charge. From there, its internal combustion engine powers an electric generator to extend the vehicle's range as needed. When the engine is running it may be periodically mechanically linked (by a clutch) to a planetary gear set, and hence the output drive axle, to improve energy efficiency. The Volt's regenerative braking also contributes to the on-board electricity generation. Under the United States Environmental Protection Agency (EPA) cycle, the 2013/15 model year Volt all-electric range is 38 mi (61 km), with a combined electric mode/gasoline-only rating of 62 mpg‑US (3.8 L/100 km; 74 mpg‑imp) equivalent (MPG-equivalent).

The second-generation Volt's improved battery system and drivetrain increased the all-electric range to 53 miles (85 km), its EPA-rated fuel economy in charge-sustaining mode to 42 mpg‑US (5.6 L/100 km; 50 mpg‑imp), and the combined city/highway fuel economy in all-electric mode to 106 MPG-e, up from 98 MPG-e. Deliveries to retail customers in the U.S. and Canada began in October 2015 as a 2016 model year.

The Volt has won several awards, including the 2009 Green Car Vision Award, 2011 Green Car of the Year, 2011 North American Car of the Year, 2011 World Green Car, 2012 European Car of the Year, and 2016 Green Car of the Year. Controversies regarding the Volt include the extent to which the U.S. federal government may have participated in the Volt’s development, which continued through General Motors' 2009 government-led bankruptcy, and concerns about the battery-pack fire risk following a crash test that the National Highway Traffic Safety Administration (NHTSA) performed on a Volt in 2011. At the completion of its investigation, NHTSA concluded that no discernible defect trend exists.

Deus vult

Deus vult ("God wills it")

(variants Deus le volt, Dieux el volt; Deus id vult, Deus hoc vult, etc.) is a Catholic motto associated with the Crusades, more specifically with the First Crusade of 1096–1099. The phrase appears in the Vulgate translation of the Christian Bible.

Electric power distribution

Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment or household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level.

Electric power transmission

Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines which facilitate this movement are known as a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. The combined transmission and distribution network is known as the "power grid" in North America, or just "the grid". In the United Kingdom, India, Malaysia and New Zealand, the network is known as the "National Grid".

A wide area synchronous grid, also known as an "interconnection" in North America, directly connects a large number of generators delivering AC power with the same relative frequency to a large number of consumers. For example, there are four major interconnections in North America (the Western Interconnection, the Eastern Interconnection, the Quebec Interconnection and the Electric Reliability Council of Texas (ERCOT) grid). In Europe one large grid connects most of continental Europe.

Historically, transmission and distribution lines were owned by the same company, but starting in the 1990s, many countries have liberalized the regulation of the electricity market in ways that have led to the separation of the electricity transmission business from the distribution business.


In physics, the electronvolt (symbol eV, also written electron-volt and electron volt) is a unit of energy equal to approximately 1.6×10−19 joules (symbol J) in SI units.

Historically, the electronvolt was devised as a standard unit of measure through its usefulness in electrostatic particle accelerator sciences, because a particle with charge q has an energy E = qV after passing through the potential V; if q is quoted in integer units of the elementary charge and the terminal bias in volts, one gets an energy in eV.

Like the elementary charge on which it is based, it is not an independent quantity but is equal to 1 J/C √2hα / μ0c0. It is a common unit of energy within physics, widely used in solid state, atomic, nuclear, and particle physics. It is commonly used with the metric prefixes milli-, kilo-, mega-, giga-, tera-, peta- or exa- (meV, keV, MeV, GeV, TeV, PeV and EeV respectively). In some older documents, and in the name Bevatron, the symbol BeV is used, which stands for billion (109) electronvolts; it is equivalent to the GeV.


The joule (/dʒuːl/; symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metre or N⋅m). It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

In terms firstly of base SI units and then in terms of other SI units:

where kg is the kilogram, m is the metre, s is the second, N is the newton, Pa is the pascal, W is the watt, C is the coulomb, and V is the volt.

One joule can also be defined as:

Judge Volt

Chief Judge Hadrian Volt is a fictional character appearing in the Judge Dredd comic strip, published by British anthology 2000 AD. He was chief judge of Mega-City One between 2116 and 2121 (appearing in the comic between 1994 and 1999).


A multimeter or a multitester, also known as a VOM (volt-ohm-milliammeter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter can measure voltage, current, and resistance. Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters (DMM, DVOM) have a numeric display, and may also show a graphical bar representing the measured value. Digital multimeters are now far more common due to their cost and precision, but analog multimeters are still preferable in some cases, for example when monitoring a rapidly varying value.

A multimeter can be a hand-held device useful for basic fault finding and field service work, or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

Multimeters are available in a wide range of features and prices. Cheap multimeters can cost less than US$10, while laboratory-grade models with certified calibration can cost more than US$5,000.

Nine-volt battery

The nine-volt battery, or 9-volt battery, is a common size of battery that was introduced for the early transistor radios. It has a rectangular prism shape with rounded edges and a polarized snap connector at the top. This type is commonly used in walkie-talkies, clocks and smoke detectors.

The nine-volt battery format is commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium iron disulfide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and lithium-ion. Mercury-oxide batteries of this format, once common, have not been manufactured in many years due to their mercury content. Designations for this format include NEDA 1604 and IEC 6F22 (for zinc-carbon) or MN1604 6LR61 (for alkaline). The size, regardless of chemistry, is commonly designated PP3—a designation originally reserved solely for carbon-zinc, or in some countries, E or E-block.Most nine-volt alkaline batteries are constructed of six individual 1.5 V LR61 cells enclosed in a wrapper. These cells are slightly smaller than LR8D425 AAAA cells and can be used in their place for some devices, even though they are 3.5 mm shorter. Carbon-zinc types are made with six flat cells in a stack, enclosed in a moisture-resistant wrapper to prevent drying. Primary lithium types are made with three cells in series.In 2007, 9-volt batteries accounted for 4% of alkaline primary battery sales in the United States. In Switzerland in 2008, 9-volt batteries totalled 2% of primary battery sales and 2% of secondary battery sales.

Roosevelt County, Montana

Roosevelt County is a county in the U.S. state of Montana. As of the 2010 United States Census, the population was 10,425. Its county seat is Wolf Point. Roosevelt County was created by the Montana Legislature in 1919 from a portion of Sheridan County. The name honors former president Theodore Roosevelt, who had died earlier that year.

Son Volt

Son Volt is an American alternative rock and alternative country band, formed by Jay Farrar in 1994 after the breakup of Uncle Tupelo.

Stax Records

Stax Records is an American record label, originally based in Memphis, Tennessee. Founded in 1957 as Satellite Records, the label changed its name to Stax Records in 1961. It was a major factor in the creation of Southern soul and Memphis soul music. Stax also released gospel, funk, and blues recordings. Renowned for its output of blues music, the label was founded by two siblings and business partners, Jim Stewart and his sister Estelle Axton (STewart/AXton = Stax). It featured several popular ethnically integrated bands (including the label's house band, Booker T. & the M.G.'s) and a racially integrated team of staff and artists unprecedented in that time of racial strife and tension in Memphis and the South.According to ethnomusicologist Rob Bowman, the label's use of "one studio, one equipment set-up, the same set of musicians and a small group of songwriters led to a readily identifiable sound. It was a sound based in black gospel, blues, country, and earlier forms of rhythm and blues. It became known as southern soul music."Following the death of Stax's biggest star, Otis Redding, in 1967, and the severance of the label's distribution deal with Atlantic Records in 1968, Stax continued primarily under the supervision of a new co-owner, Al Bell. Over the next five years, Bell expanded the label's operations significantly, in order to compete with Stax's main rival, Motown Records in Detroit. During the mid-1970s, a number of factors, including a problematic distribution deal with CBS Records, caused the label to slide into insolvency, resulting in its forced closure in late 1975.In 1977, Fantasy Records acquired the post-1968 Stax catalogue and selected pre-1968 recordings. Beginning in 1978, Stax (now owned by Fantasy) began signing new acts and issuing new material, as well as reissuing previously recorded Stax material. However, by the early 1980s, no new material was being issued on the label, and for the next two decades, Stax was strictly a reissue label.

After Concord Records acquired Fantasy in 2004, the Stax label was reactivated, and is today used to issue both the 1968–1975 catalog material and new recordings by current R&B and soul performers. Atlantic Records continues to hold the rights to the vast majority of the 1959–1968 Stax material.


A volt-ampere (VA) is the unit used for the apparent power in an electrical circuit, equal to the product of root-mean-square (RMS) voltage and RMS current. In direct current (DC) circuits, this product is equal to the real power (active power) in watts. Volt-amperes are useful only in the context of alternating current (AC) circuits (sinusoidal voltages and currents of the same frequency).

With a purely resistive load, the apparent power is equal to the real power. Where a reactive (capacitive or inductive) component is present in the load, the apparent power is greater than the real power as voltage and current are no longer in phase. In the limiting case of a purely reactive load, current is drawn but no power is dissipated in the load.

Some devices, including uninterruptible power supplies (UPSs), have ratings both for maximum volt-amperes and maximum watts. The VA rating is limited by the maximum permissible current, and the watt rating by the power-handling capacity of the device. When a UPS powers equipment which presents a reactive load with a low power factor, neither limit may safely be exceeded. For example, a (large) UPS system rated to deliver 400,000 volt-amperes at 220 volts can deliver a current of 1818 amperes.

VA ratings are also often used for transformers; maximum output current is then VA rating divided by nominal output voltage. Transformers with the same sized core usually have the same VA rating.

The convention of using the volt-ampere to distinguish apparent power from real power is allowed by the SI standard.

Volt Europa

Volt Europa (frequently abbreviated Volt) is a pro-European political movement that serves as the pan-European structure of EU parties for the European Parliament elections in May 2019. It was founded in 2017 by Andrea Venzon, supported by Colombe Cahen-Salvador and Damian Boeselager. The organisation follows a "pan-European approach" in many policy fields such as climate change, migration, economic inequality, international conflict, terrorism and the impact of the technological revolution on the labour market.


Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points. The difference in electric potential between two points (i.e., voltage) in a static electric field is defined as the work needed per unit of charge to move a test charge between the two points. In the International System of Units, the derived unit for voltage is named volt. In SI units, work per unit charge is expressed as joules per coulomb, where 1 volt = 1 joule (of work) per 1 coulomb (of charge). The official SI definition for volt uses power and current, where 1 volt = 1 watt (of power) per 1 ampere (of current). This definition is equivalent to the more commonly used 'joules per coulomb'. Voltage or electric potential difference is denoted symbolically by ∆V, but more often simply as V, for instance in the context of Ohm's or Kirchhoff's circuit laws.

Electric potential differences between points can be caused by electric charge, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage (or potential difference) between two points in a system; often a common reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy (electromotive force) or lost, used, or stored energy (potential drop).


A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.

A voltmeter in a circuit diagram is represented by the letter V in a circle.

Voltmeters are made in a wide range of styles. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.

General purpose analog voltmeters may have an accuracy of a few percent of full scale, and are used with voltages from a fraction of a volt to several thousand volts. Digital meters can be made with high accuracy, typically better than 1%. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Meters using amplifiers can measure tiny voltages of microvolts or less.

Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the Weston Cell is used as a standard voltage for precision work. Precision voltage references are available based on electronic circuits.

Wario (series)

The Wario (ワリオ) franchise comprises various video games created by Nintendo, starring the character Wario. The franchise began with Wario Land: Super Mario Land 3, the first game to feature Wario as a playable character, and gained many further installments. The Wario series includes mostly platforming video games and minigame compilations, but also includes other genres. It is a spin-off of the Mario series.

Weber (unit)

In physics, the weber (symbol: Wb) is the SI derived unit of magnetic flux. A flux density of one Wb/m2 (one weber per square metre) is one tesla.

The weber is named after the German physicist Wilhelm Eduard Weber (1804–1891).

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