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The volt (symbol: V) is the SI
Si

Si, si, or SI may refer to :...
 derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electric potential difference
Potential difference

In physics, the potential difference or p.d. between two points is the difference of the points' scalar potential, equivalent to the line integral of the field strength between the two points....
 or electromotive force
Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
, commonly known as voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
. It is named in honor of the Lombard physicist Alessandro Volta
Alessandro Volta

Count Alessandro Antonio Anastasio Volta was a Lombardy Physics known especially for the development of the first cell in 1800....
  (1745–1827), who invented the voltaic pile
Voltaic pile

A voltaic pile is a set of individual Galvanic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first battery ....
, possibly the first chemical battery
Battery (electricity)

In electronics, a battery or voltaic cell is a combination of one or more electrochemical cell Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity....
 (see Baghdad Battery
Baghdad Battery

The Baghdad Battery, sometimes referred to as the Parthian Battery, is the common name for a number of artifacts created in Mesopotamia, possibly during the Parthian or Sassanid period ....
).

lt is defined as the potential difference
Potential difference

In physics, the potential difference or p.d. between two points is the difference of the points' scalar potential, equivalent to the line integral of the field strength between the two points....
 across a conductor when a current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
 of one ampere
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
 dissipates one watt
WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
 of power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
.






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Nistvoltchip
The volt (symbol: V) is the SI
Si

Si, si, or SI may refer to :...
 derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of electric potential difference
Potential difference

In physics, the potential difference or p.d. between two points is the difference of the points' scalar potential, equivalent to the line integral of the field strength between the two points....
 or electromotive force
Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
, commonly known as voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
. It is named in honor of the Lombard physicist Alessandro Volta
Alessandro Volta

Count Alessandro Antonio Anastasio Volta was a Lombardy Physics known especially for the development of the first cell in 1800....
  (1745–1827), who invented the voltaic pile
Voltaic pile

A voltaic pile is a set of individual Galvanic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first battery ....
, possibly the first chemical battery
Battery (electricity)

In electronics, a battery or voltaic cell is a combination of one or more electrochemical cell Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity....
 (see Baghdad Battery
Baghdad Battery

The Baghdad Battery, sometimes referred to as the Parthian Battery, is the common name for a number of artifacts created in Mesopotamia, possibly during the Parthian or Sassanid period ....
).

Definition

A volt is defined as the potential difference
Potential difference

In physics, the potential difference or p.d. between two points is the difference of the points' scalar potential, equivalent to the line integral of the field strength between the two points....
 across a conductor when a current
Electric current

Electric current is the flow of electric charge. The electric charge may be either electrons or ions.The International System of Units unit of electric current intensity is the ampere....
 of one ampere
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
 dissipates one watt
WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
 of power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
. Hence, it is the base SI representation m
Metre

The metre or meter is a Unit of measurement of length. It is the SI base unit of length in the metric system and in the International System of Units , used around the world for general and scientific purposes....
2 · kg
Kilogram

The kilogram or kilogrammeThe spelling kilogram is used by the International Committee for Weights and Measures and the U.S....
 · s
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
-3 · A
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
-1, which can be equally represented as one joule
Joule

The joule is the SI derived unit of energy in the International System of Units. It is defined as:One joule is the amount of energy required to perform the following actions:...
 of energy
Energy

In physics, energy is a scalar physical quantity that describes the amount of Work_ that can be performed by a force. Energy is an attribute of objects and systems that is subject to a conservation law....
 per coulomb
Coulomb

The coulomb is the SI unit of electric charge. It is named after Charles-Augustin de Coulomb....
 of charge, J/C.

Josephson junction definition

Since 1990 the volt has been maintained internationally for practical measurement using the Josephson effect
Josephson effect

The Josephson effect is the phenomenon of current flow across two weakly coupled superconductors, separated by a very thin insulating barrier. This arrangement?two superconductors linked by a non-conducting barrier?is known as a Josephson junction; the current that crosses the barrier is the Josephson current....
, where a conventional value is used for the Josephson constant, fixed by the 18th General Conference on Weights and Measures
General Conference on Weights and Measures

The General Conference on Weights and Measures is the English name of the Conf?rence g?n?rale des poids et mesures . It is one of the three organizations established to maintain the International System of Units under the terms of the Convention du M?tre of 1875....
 as:

K = 0.4835979 GHz/µV.


Hydraulic analogy

In the hydraulic analogy
Hydraulic analogy

The electronic–hydraulic analogy is the most widely used analogy for "electron fluid" in a metal conductor. Since electric current is invisible and the processes at play in electronics are often difficult to demonstrate, the various electronic components are represented by hydraulic equivalents....
 sometimes used to explain electric circuits by comparing them to water-filled pipes, voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
 is likened to water pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
 – it determines how quickly the electrons will travel through the circuit. Current (in amperes), in the same analogy, is a measure of the volume of water that flows past a given point per unit time (volumetric flow rate
Volumetric flow rate

The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time Volumetric flow rate should not be confused with volumetric flux, as defined by Darcy's law and represented by the symbol q, with units of m3/, that is, m s-1....
). The flow rate is determined by the width of the pipe (analogous to electrical resistance
Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electrical current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material....
) and the pressure difference between the front end of the pipe and the exit (potential difference
Potential difference

In physics, the potential difference or p.d. between two points is the difference of the points' scalar potential, equivalent to the line integral of the field strength between the two points....
 or voltage
Voltage

Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
). The analogy extends to power dissipation: the power given up by the water flow is equal to flow rate times pressure, just as the power dissipated in a resistor is equal to current times the voltage drop across the resistor (amperes x volts = watts).

The relationship between voltage and current (in ohmic devices) is defined by Ohm's Law
Ohm's law

Ohm's law applies to electrical circuits; it states that the electric current through a conductor between two points is directly Proportionality to the potential difference or voltage across the two points, and inversely proportional to the Electrical resistance between them....
.

Common voltages

Electronic Multi Meter
Bateriar14
Nominal voltages of familiar sources:
  • Nerve cell resting potential
    Resting potential

    Relatively static membrane potential of quiescent cells is called resting membrane potential , as opposed to the specific dynamic electrochemical phenomenona called action potential and graded membrane potential....
    : around -75 mV
  • Single-cell, rechargeable NiMH
    Nickel metal hydride battery

    A nickel-metal hydride cell, abbreviated NiMH, is a type of rechargeable battery similar to Nickel Hydrogen cell. The NiMH battery uses a hydrogen-absorbing alloy for the negative electrode instead of cadmium....
     or NiCd
    Nickel-cadmium battery

    The nickel-cadmium battery is a type of rechargeable battery using nickel oxide hydroxide and metallic cadmium as electrodes.The abbreviation NiCad is a registered trademark of SAFT Corporation and should not be used to refer generically to nickel-cadmium batteries, although this brand-name is genericized trademark to describe all ni...
     battery: 1.2 V
  • Mercury battery
    Mercury battery

    A mercury battery is a non-rechargeable battery , a primary cell. Due to the content of Mercury , and the resulting environmental concerns, the sale of mercury batteries is banned in many countries....
    : 1.355 V
  • Single-cell, non-rechargeable alkaline battery
    Alkaline battery

    Alkaline batteries and alkaline cells are a type of disposable battery or Rechargeable alkaline battery battery dependent upon the reaction between zinc and manganese oxide ....
     (e.g. AAA, AA, C and D cells
    Battery (electricity)

    In electronics, a battery or voltaic cell is a combination of one or more electrochemical cell Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity....
    ): 1.5 V
  • Lithium polymer rechargeable battery: 3.75 V
  • Transistor-transistor logic
    Transistor-transistor logic

    File:68k ttl.jpgTransistor?transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor?transistor logic because both the logic gating function and the amplifying function are performed by transistors ....
    /CMOS
    CMOS

    Complementary metal?oxide?semiconductor , is a major class of integrated circuits. CMOS technology is used in microprocessors, microcontrollers, Static Random Access Memory, and other digital logic circuits....
     (TTL) power supply: 5 V
  • PP3 battery
    PP3 battery

    A PP3 battery , commonly referred to simply as a nine-volt battery, is shaped as a rounded rectangular prism and has a nominal output of nine volts....
    : 9 V
  • Automobile
    Automobile

    An automobile or motor car is a wheeled motor vehicle for transportation passengers, which also carries its own car engine or motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally f...
     electrical system: "12 V", about 11.8 V discharged, 12.8 V charged, and 13.8-14.4 V while charging (vehicle running).
  • Household mains electricity
    Mains electricity

    Mains is the general-purpose alternating current electric power supply. The term is not often used in the United States and Canada. In the US, mains power is referred to by a variety of formal and informal names, including household power, household electricity, domestic power, wall power, line power, AC p...
    : 240 V RMS
    Root mean square

    In mathematics, the root mean square , also known as the quadratic mean, is a statistics measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
     in Australia, 230 V RMS in Europe, Asia and Africa, 120 V RMS in North America, 100 V RMS in Japan (see List of countries with mains power plugs, voltages and frequencies
    List of countries with mains power plugs, voltages and frequencies

    Wall socketsThe lettering system used here is from a U.S. government document, which defines the letter names and gives a list of what plug types are used where....
    )
  • Commercial and Military Jet aircraft: 400 V AC, 28 V DC
  • Trucks
    Trucks

    Trucks may refer to:*The plural of truck*The ground billiards game otherwise known as troco or lawn billiards*The Trucks, a band*Trucks , a band...
    /lorries: 24 V DC
  • Rapid transit
    Rapid transit

    A rapid transit, subway, underground, elevated railway or metro system is an railway electrification system public transport rail transport in an urban area with high capacity and frequency, and which is grade separation from other traffic....
     third rail
    Third rail

    A third rail is a method of providing electricity to power a rail transport through a continuous rigid conductor alongside the railway track or between the rails....
    : 600 to 750 V (see List of current systems for electric rail traction
    List of current systems for electric rail traction

    This a list of the supply voltages used or have been used for tramway and railway electrification system.Note the voltages are nominal, and vary depending on load and distance from the substation....
    )
  • High speed train overhead power lines: 25 kV RMS at 50 Hz, but see the list of current systems for electric rail traction
    List of current systems for electric rail traction

    This a list of the supply voltages used or have been used for tramway and railway electrification system.Note the voltages are nominal, and vary depending on load and distance from the substation....
     for exceptions.
  • High voltage electric power transmission
    Electric power transmission

    Electric power transmission is the bulk transfer of electrical power , a process in the delivery of electricity to consumers. A power transmission grid typically connects power plants to multiple Electrical substation near a populated area....
     lines: 110 kV RMS and up (1150 kV RMS was the record as of 2005)
  • Lightning
    Lightning

    File:Blesk.jpgLightning is an Earth's atmosphere discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcano or dust storms....
    : Varies greatly, often around 100 MV.


Note: Where 'RMS' (root mean square
Root mean square

In mathematics, the root mean square , also known as the quadratic mean, is a statistics measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
) is stated above, the peak voltage is times greater than the RMS voltage for a sinusoidal signal centered around zero voltage.

History of the volt

In 1800, as the result of a professional disagreement over the galvanic response advocated by Luigi Galvani
Luigi Galvani

Luigi Galvani was an Italy physician and physicist who lived and died in Bologna. In 1771, he discovered that the muscles of dead frogs twitched when struck by a spark....
, Alessandro Volta
Alessandro Volta

Count Alessandro Antonio Anastasio Volta was a Lombardy Physics known especially for the development of the first cell in 1800....
 developed the so-called Voltaic pile
Voltaic pile

A voltaic pile is a set of individual Galvanic cells placed in series. The voltaic pile, invented by Alessandro Volta in 1800, was the first battery ....
, a forerunner of the battery
Battery (electricity)

In electronics, a battery or voltaic cell is a combination of one or more electrochemical cell Galvanic cells which store chemical energy that can be converted into electric potential energy, creating electricity....
, which produced a steady electric current. Volta had determined that the most effective pair of dissimilar metals to produce electricity was zinc
Zinc

Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal of the group 12 element of the periodic table....
 and silver
Silver

Silver is a chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal....
. In the 1880s, the International Electrical Congress, now the International Electrotechnical Commission
International Electrotechnical Commission

The International Electrotechnical Commission is a Non-profit organization, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies ? collectively known as "electrotechnology"....
 (IEC), approved the volt for electromotive force. At that time, the volt was defined as the potential difference across a conductor when a current of one ampere
Ampere

The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....
 dissipates one watt
WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
 of power.

The international volt was defined in 1893 as 1/1.434 of the emf
Electromotive force

Electromotive force is a term used to characterize electrical devices, such as voltaic cells, Thermoelectric effects, electrical generators and transformers, and even resistors....
 of a Clark cell
Clark cell

The Clark cell, invented by English engineer Josiah Latimer Clark in 1873, is a wet cell that produces a highly stable voltage usable as alaboratory standard....
. This definition was abandoned in 1908 in favor of a definition based on the international ohm
Ohm

The ohm is the SI unit of electrical impedance or, in the direct current case, electrical resistance, named after Georg 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 cell
Weston cell

The Weston cell, invented by Edward Weston in 1893, is a wet cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters....
s. The United States used a design called the Weston cell
Weston cell

The Weston cell, invented by Edward Weston in 1893, is a wet cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters....
 from 1905 to 1972.

See also

  • SI
    Si

    Si, si, or SI may refer to :...
     for unit prefixes
  • SI electromagnetism units
    SI electromagnetism units

    See also* SI units* Speed of light* meter* ampere* secondReferences...
  • Voltage
    Voltage

    Electrical tension is the potential difference between two points of an electrical or electronic circuit, expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor....
  • Voltmeter
    Voltmeter

    A voltmeter is an instrument used for measuring the 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....
  • Watt
    WATT

    WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
  • Ampere
    Ampere

    The ampere is the International System of Units unit of electric current. The ampere, in practice often shortened to amp, is an SI base unit, and is named after Andr?-Marie Amp?re, one of the main discoverers of electromagnetism....


External links