volt

The International System unit of electric potential and electromotive force, equal to the difference of electric potential between two points on a conducting wire carrying a constant current of one ampere when the power dissipated between the points is one watt.

[After Count Alessandro VOLTA.]

1. A circular movement executed by a horse in manège.
2. A sudden movement made in avoiding a thrust in fencing.

[French volte, from Italian volta, turn, from voltare, to turn, leap. See vault².]

Symbol V. The SI unit of electric potential, potential difference, or e.m.f. defined as the difference of potential between two points on a conductor carrying a constant current of one ampere when the power dissipated between the points is one watt. It is named after Alessandro Volta.

The unit of electromotive force, the volt measures how much “pressure” there is in an electrical circuit. The higher the voltage, the more electrical current will flow in the circuit.Ordinary household outlets are usually rated at 115 volts, car batteries at 12 volts, and flashlight batteries at 1.5 volts.

A unit of measurement of force, or pressure, in an electrical circuit. The common voltage of an AC power line is 120 volts of alternating current (alternating directions). Common voltages within a computer are from 3 to 12 volts of direct current (one direction only). See voltage and volt-amps.

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The unit of electromotive force or electrical pressure; the force necessary to cause 1 ampere of current to flow against 1 ohm of resistance. A volt is the unit that is used to measure the tendency of a charge to move from one place to another.

[Etymology: A. G. A. Anastassio, Count Volta; Italy 1745-1827] voltage, electromotive force, potential difference. Symbol V. The electromotive force or potential difference in volts between two points of a steady current equals the ratio of power produced in watts to the current strength in amperes; equally the product of current strength in amperes and resistance in ohms. V = W·A^-1 = A·Ω.

SI, Metric-m.k.s.A. (= m²·kg·s^-3·A^-1 in base terms). The following are among the coherent derived units:

• V·m^-1 for electric field strength;
• V·s = weber for magnetic flux;
• V·A for apparent power;
• V·A^-1 = ohm for electric resistance.

Metric-c.g.s. See abvolt (a base unit for the e.m.u. system); statvolt. See also practical unit.

UK 1 MV = 1 crocodile.

History

The volt as used today was originally defined in 1881 at the first International Electrical Conference,
[Nature Vol. 24, 512 (1881)] among the practical units derived from the absolute units of the e.m.u. system. It was set at 10⁸ times the volt of that system i.e. 1 practical volt = 10⁸ abvolt. Like all the e.m. units, the abvolt was itself defined in terms of purely mechanical units; it had been initiated in the 1860s as the ohma.

Initially an explicit laboratory specification of the volt was established by the International Electrical Conference, making it a base unit instead of a derived unit. Expressed in terms of the potential of the common voltaic cell of the time, the specification was subsequently shown to have made the volt slightly larger than intended and not precisely consistent with the independently defined ampere and ohm.
[Nature Vol. 78, 678-81 (1908)] The IEC of 1908 took away the inconsistency by making the volt a derived unit from those others, but this still had a derived discrepancy from intent, so the Conference adopted the distinct name international volt, lacking reference to being absolute or practical (though it was the latter). Because of experimental vagaries, the value for conversions is normally referred to as the mean international volt, V_M = 1.000 34 V.
[Nature Vol. 163, 427-8 (1949)] There is also the US international volt, = 1.000 330~ V, defined by Congress in an Act of 1894.

With the implementation of the m.k.s.A. system in 1948, and its basing of electrical units on an ampere compatible with the original absolute units, the modern volt became essentially the old practical volt; this became identically the volt of the SI.

The calibration of reference electrical instruments from the fundamental definition presents obvious practical problems of accuracy. Until the 1980s the method involved weighing on a balance the magnetic force between two coils of carefully measured copper wire; this gave an accuracy of barely 1 in 10⁵. For maximum accuracy, the volt is now realized using the Josephson effect that applies at very low temperatures with superconductors, via the Josephson constant, which relates volts to frequency.
[Hartland A. Contemp. Phys. Vol. 29, 477 (1988) http://www.npl.co.uk/npl/publications/electricity/] Together with subsequent development of the moving-coil balance, this allows accuracy better than 1 in 10⁸.

Revised conventional values for the constants involved in laboratory realizations using these effects, adopted internationally beginning in 1990, resulted in reducing the resistance value of many laboratory standards by about 0.000 8%.
[Kibble B., Hartland A. New Scientist Vol. 1715, 48-51 (1990)]

In electric systems the unit of potential difference or electromotive force; when applied across a resistance of 1 ohm, will result in a current flow of 1 ampere.

The SI unit of potential difference, electromotive force, and electric potential. One volt is the difference in potential between two conducting points carrying a current of 1 amp when the power dissipated between these points is 1 W.

The unit of electromotive force; 1 ampere of current against 1 ohm of resistance.

• electron v. (eV) — a unit of energy equal to the energy acquired by an electron in being accelerated through a potential difference of 1 volt; equal to 1.602 × 10⁻¹⁹ joule.
• gigaelectron v. (GeV) — one thousand million electron volts (10⁹ eV).
• kiloelectron v. (keV) — one thousand electron volts (10³ eV).
• megaelectron v. (MeV) — one million electron volts (10⁶ eV).

To convert from volt inch to:

volt/cm, multiply by .3937.
statvolts, multiply by .003336.

Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm.

For other uses, see Volt (disambiguation).

Look up volt in Wiktionary, the free dictionary.

Josephson junction array chip developed by NIST as a standard volt.

The volt (symbol: V) is the SI derived unit of electromotive force, commonly called "voltage".^[1] It is also the unit for the related but slightly different quantity electric potential difference (also called "electrostatic potential difference"). It is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, possibly the first chemical battery (see Baghdad Battery).

Contents 1 Definition 1.1 Josephson junction definition 2 Water flow analogy 3 Common voltages 4 History of the volt 5 See also 6 References 7 External links

Definition

The volt is defined as the value of the voltage across a conductor when a current of one ampere dissipates one watt of power in the conductor. ^[2] It can be written in terms of SI base units as: m² · kg · s⁻³ · A⁻¹. It is also equal to one joule of energy per coulomb of charge, J/C.

Josephson junction definition

Since 1990 the volt has been maintained internationally for practical measurement using the Josephson effect, where a conventional value is used for the Josephson constant, fixed by the 18th General Conference on Weights and Measures as:

K_{J-90} = 0.4835979 GHz/µV.

Water flow analogy

In the water flow analogy sometimes used to explain electric circuits by comparing them to water-filled pipes, voltage difference is likened to water pressure difference – the difference 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). The flow rate is determined by the width of the pipe (analogous to electrical resistance), and the pressure difference between the front end of the pipe and the exit is analogous to voltage. 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.

Common voltages

A multimeter can be used to measure the voltage between two positions.

1.5 V C-cell batteries

Nominal voltages of familiar sources:

• Nerve cell resting potential: around -75 mV^[3]
• Single-cell, rechargeable NiMH or NiCd battery: 1.2 V
• Mercury battery: 1.355 V
• Single-cell, non-rechargeable alkaline battery (e.g. AAA, AA, C and D cells): 1.5 V
• Lithium polymer rechargeable battery: 3.75 V
• Transistor-transistor logic/CMOS (TTL) power supply: 5 V
• PP3 battery: 9 V
• Automobile 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: 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)
• Commercial and Military Jet aircraft: 400 V AC, 28 V DC
• Trucks/lorries: 24 V DC
• Rapid transit third rail: 600 to 750 V (see List of current systems for electric rail traction)
• High speed train overhead power lines: 25 kV RMS at 50 Hz, but see the list of current systems for electric rail traction and 25 kV at 60 Hz for exceptions.
• High voltage electric power transmission lines: 110 kV RMS and up (1150 kV RMS was the record as of 2005)
• Lightning: Varies greatly, often around 100 MV.

Note: Where 'RMS' (root mean square) 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, 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 the 1880s, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force. 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.

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.

This SI unit is named after Alessandro Volta. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is uppercase (V). When an SI unit is spelled out in English, it should always begin with a lowercase letter (volt), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.

—Based on The International System of Units, section 5.2.

See also

25 kV AC Ampere Electric potential difference

Rail traction voltage SI electromagnetism units SI for unit prefixes

Voltage Voltmeter Watt

References

1. ^ "SI Brochure, Table 3 (Section 2.2.2)". BIPM. 2006. http://www.bipm.org/en/si/si_brochure/chapter2/2-2/table3.html. Retrieved 2007-07-29. 
2. ^ BIPM SI Brochure: Appendix 1, p. 144
3. ^ Bullock, Orkand, and Grinnell, pp. 150–151; Junge, pp. 89–90; Schmidt-Nielsen, p. 484

External links

• Google Video Lecture about Electricity and Volt by Richard A. Muller
• What is RMS?

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
1.
n. - volt

2.
n. - variant af volte
v. intr. - at lave hurtigt udfald i fægtning

Nederlands (Dutch)
volt, sprong in schermen, rondgaande beweging van paard

Français (French)
1.
n. - (Élec) volt

2.
n. - volte
v. intr. - (Sport) faire un mouvement rapide pour éviter un coup d'estoc (escrime)

Deutsch (German)
1.
n. - Volt

2.
n. - Volte
v. - ausweichen

Ελληνική (Greek)
n. - (φυσ.) βολτ
v. - κάνω μεταβολή

Italiano (Italian)
volt

Português (Portuguese)
n. - volt (m) (Eletr.), volteio (m) (Desp.), salto para evitar um golpe (m) (Desp.)
v. - voltear (Equit.), mover-se rápido para evitar um ataque (Desp.)

Русский (Russian)
вольт, уклониться от удара противника

Español (Spanish)
1.
n. - voltio, volt

2.
n. - giro, vuelta
v. intr. - hacer un movimiento brusco, esquivar

Svenska (Swedish)
n. - volt
v. - volta

中文（简体）(Chinese (Simplified))
1. 伏特

2. 环骑, 闪避

中文（繁體）(Chinese (Traditional))
1.
n. - 伏特

2.
n. - 環騎, 閃避

한국어 (Korean)
1.
n. - 볼트 (전압의 실용 단위)

2.
n. - 찌르기를 피하기 위한 재빠른 다리의 동작, 회전
v. intr. - 찌르기를 피하기 위하여 재빨리 몸을 비키다

日本語 (Japanese)
n. - ボルト

العربيه (Arabic)
‏(الاسم) فولت ( وحدة القوة الكهربائيه)‏

עברית (Hebrew)
n. - ‮וולט (יחידת מתח חשמלי)‬
n. - ‮איות נוסף של ETLOV‬
v. intr. - ‮עשה תנועה מהירה כדי לחמוק מדקירה (סיוף)‬

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