Josephson junction array chip developed by NIST as a standard volt

The volt (symbol: V) is the SI derived unit for electric potential, electric potential difference, and electromotive force.^[1] The volt is named in honor of the Italian physicist Alessandro Volta (1745–1827), who invented the voltaic pile, possibly the first chemical battery.

Definition[link]

A single volt is defined as the difference in electric potential across a wire when an electric current of one ampere dissipates one watt of power.^[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 units as follows:

Failed to parse (Missing texvc executable; please see math/README to configure.): \mbox{V} = \mbox{A} \cdot \Omega= \dfrac{\mbox{W}}{\mbox{A}} = \sqrt{\mbox{W} \cdot \Omega} = \dfrac{\mbox{J}}{\mbox{A} \cdot \mbox{s}} = \dfrac{\mbox{N} \cdot \mbox{m} }{\mbox{A} \cdot \mbox{s}} = \dfrac{\mbox{kg} \cdot \mbox{m}^2}{\mbox{C} \cdot \mbox{s}^2} = \dfrac{\mbox{N} \cdot \mbox{m}} {\mbox{C}} = \dfrac{\mbox{J}}{\mbox{C}}

It can also be written using only the SI base units m, kg, s, and A as:

Failed to parse (Missing texvc executable; please see math/README to configure.): \mbox{V} = \dfrac{\mbox{kg} \cdot \mbox{m}^2}{\mbox{A} \cdot \mbox{s}^{3}}

Josephson junction definition[link]

Between 1990 and 1997, the volt was calibrated using the Josephson effect for exact voltage-to-frequency conversion, combined with cesium-133 time reference, as decided by the 18th General Conference on Weights and Measures. The following value for the Josephson constant is used:

K_{J-90} = 2e/h = 0.4835979 GHz/µV.

This is typically used with an 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] However, as of July 2007, this is not the official BIPM definition of Volt.^[5]

Water flow analogy[link]

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

Common voltages[link]

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^[6]
• 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
• LiFePO₄ rechargeable battery: 3.3 V
• Lithium polymer rechargeable battery: 3.75 V (see Rechargeable battery#Table of rechargeable battery technologies)
• Transistor-transistor logic/CMOS (TTL) power supply: 5 V
• PP3 battery: 9 V
• Automobile electrical system: nominal 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)
• Trucks/lorries: 24 V DC
• Rapid transit third rail: 600–750 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 (1.15 MV RMS was the record as of 2005^{[citation needed]})
• Lightning: Varies greatly, often around 100 MV.

Note: Where RMS (root mean square) is stated above, the peak voltage is Failed to parse (Missing texvc executable; please see math/README to configure.): \sqrt{2}

times greater than the RMS voltage for a sinusoidal signal centered around zero voltage.

History of the volt[link]

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 is 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 International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (V). When an SI unit is spelled out in English, it should always begin with a lower case 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[link]

References[link]

External links[link]

Look up volt in Wiktionary, the free dictionary.

• Google Video Lecture about Electricity and Volt by Richard A. Muller

v t e SI units Base units Ampere · Candela · Kelvin · Kilogram · Metre · Mole · Second Derived units Becquerel · Coulomb · Degree Celsius · Farad · Gray · Henry · Hertz · Joule · Katal · Lumen · Lux · Newton · Ohm · Pascal · Radian · Siemens · Sievert · Steradian · Tesla · Volt · Watt · Weber Accepted for use with SI Dalton (Atomic mass unit) · Astronomical unit · Day · Decibel · Degree Celsius · Degree of arc · Electronvolt · Hectare · Hour · Litre · Minute · Minute of arc · Neper · Second of arc · Tonne Atomic units · Natural units See also SI prefixes · Systems of measurement · Conversion of units · New SI definitions · History of the metric system Book:International System of Units  · Category:SI base units

Simona de Silvestro
Simona de Silvestro in May 2010.
Nationality	Swiss
Born	(1988-09-01) September 1, 1988 (age 23) Thun, Switzerland
2012 IZOD IndyCar Series
Debut season	2010
Current team	HVM Racing
Car no.	78
Starts	35
Wins	0
Poles	0
Fastest laps	1
Best finish	19th in 2010
Previous series
2007–2009 2006 2005	Atlantic Championship Formula BMW USA Formula Renault 2.0 Italia
Awards
2010 IndyCar Series	Tony Renna Rising Star Award

Simona de Silvestro (born September 1, 1988) is a Swiss race car driver from Thun, Switzerland. She is currently competing for HVM Racing in the IZOD IndyCar Series. One nickname which has been applied to her is "The Iron Maiden".^[1]

Racing career[link]

de Silvestro at the Indianapolis Motor Speedway in 2010.

She raced for Newman Wachs Racing's Nuclear Clean Air Energy/Entergy team in the Atlantic Championship in 2008 and for Team Stargate Worlds in 2009. She won the Atlantic race at the 2008 Long Beach Grand Prix, making her the second woman to win in that series and providing NWR with its first win.^[2] She won four times during the 2009 season and led in points for most of the season. She ultimately finished third in the standings after retiring on the first lap during the season finale at Laguna Seca.

de Silvestro participated in an IRL IndyCar Series test on December 8 and 9, 2009 at Sebring International Raceway, a joint effort between HVM Racing and Team Stargate Worlds.^[3] de Silvestro competed full–time in the IRL IndyCar Series for HVM Racing for the 2010 season. On May 22, 2010, she qualified in the 22nd position for the 2010 Indianapolis 500. She finished the race in 14th position, and earned Rookie of the Year honors. She suffered a burned right hand after a fiery crash at the Firestone 550 at Texas Motor Speedway on June 5, 2010. HVM Racing strongly criticized IZOD IndyCar Series safety officials for their response to that accident.^[4]

2011[link]

The 2011 season began with promising fourth and ninth place finishes at St. Petersburg and Barber; however the next race at Long Beach was not as successful: she started 18th and finished 20th. At the next race, the São Paulo Indy 300, an accident between her and Helio Castroneves put her nine laps down, after the race was postponed to the next morning due to severe rain conditions. She also received criticism from broadcasters during the race as she raced hard against the leaders even when she was several laps down, rather than letting them pass. She started 13th and finished 20th, nine laps down, but recorded the fastest lap of the race.

She received second degree burns on her right hand and superficial burns on her left hand in a crash during practice for the 2011 Indianapolis 500 on May 19th.^[5] The crash, which sent her car sailing into the catch fence before flipping and landing on its left tires, was caused by mechanical failure in the left rear of her No. 78 Dallara/Honda. On May 21st, using her backup car, she qualified 24th for the race with a four-lap average of 224.392 mph.

After a crash at the Milwaukee Mile during qualifying, de Silvestro was cleared to drive in the race. but withdrew from the race after experiencing dizziness and impaired vision. At the next race in Iowa, she was not cleared to compete due to continuing dizziness.^[6]

De Silvestro missed Round 13 of the season at Sonoma, after being refused entry to the United States. She finished 20th overall in the 2011 series standings.

Motorsports career results[link]

Career Summary[link]

American open–wheel racing results[link]

(key) (Races in bold indicate pole position) (Races in italics indicate fastest lap)

Atlantic Championship/Champ Car Atlantic[link]

** Podium (Non-win) indicates 2nd or 3rd place finishes.

*** Top 10s (Non-podium) indicates 4th through 10th place finishes.

IndyCar Series[link]

¹ The Las Vegas Indy 300 was abandoned after Dan Wheldon died from injuries sustained in a 15-car crash on lap 11.

* Season in progress

** Podium (Non-win) indicates 2nd or 3rd place finishes.

*** Top 10s (Non-podium) indicates 4th through 10th place finishes.

Indianapolis 500[link]

References[link]

Wikimedia Commons has media related to: Simona de Silvestro

External links[link]

• Official website
• Simona de Silvestro career statistics at Driver Database
• IndyCar Driver Page
• IndyCar 11 in '11 video A