coulomb | |
---|---|

Unit system | SI derived unit |

Unit of | Electric charge |

Symbol | C |

Named after | Charles-Augustin de Coulomb |

Conversions | |

1 C in ... | ... is equal to ... |

SI base units | A⋅s |

CGS units | 2997924580 statC |

Atomic units | 6.241509074 e ×10^{18}^{ [1] } |

The **coulomb** (symbol: **C**) is the International System of Units (SI) unit of electric charge. Under the 2019 redefinition of the SI base units, which took effect on 20 May 2019,^{ [2] } the coulomb is exactly 1/(1.602176634×10^{−19}) elementary charges. The same number of electrons has the same magnitude but opposite sign of charge, that is, a charge of −1 C.

The coulomb is named after Charles-Augustin de Coulomb . As with every SI unit named for a person, its symbol starts with an upper case letter (C), but when written in full it follows the rules for capitalisation of a common noun ; i.e., "*coulomb*" becomes capitalised at the beginning of a sentence and in titles, but is otherwise in lower case.^{ [3] }

The SI system defines the coulomb in terms of the ampere and second: 1 C = 1 A × 1 s.^{ [4] } The 2019 redefinition of the ampere and other SI base units fixed the numerical value of the elementary charge when expressed in coulombs, and therefore fixed the value of the coulomb when expressed as a multiple of the fundamental charge (the numerical values of those quantities are the multiplicative inverses of each other). The ampere is defined by taking the fixed numerical value of the elementary charge e to be 1.602176634×10^{−19} coulombs.^{ [5] }

Thus, one coulomb is the charge of approximately 6241509074460762607.776 elementary charges, where the number is the reciprocal of 1.602176634×10^{−19} C.^{ [6] } It is impossible to realize exactly 1 C of charge, since it is not an integer number of elementary charges.

By 1878, the British Association for the Advancement of Science had defined the volt, ohm, and farad, but not the coulomb.^{ [7] } In 1881, the International Electrical Congress, now the International Electrotechnical Commission (IEC), approved the volt as the unit for electromotive force, the ampere as the unit for electric current, and the coulomb as the unit of electric charge.^{ [8] } 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 coulomb (later "absolute coulomb" or "abcoulomb" for disambiguation) was part of the EMU system of units. The "international coulomb" based on laboratory specifications for its measurement was introduced by the IEC in 1908. The entire set of "reproducible units" was abandoned in 1948 and the "international coulomb" became the modern coulomb.^{ [9] }

Submultiples | Multiples | |||||
---|---|---|---|---|---|---|

Value | SI symbol | Name | Value | SI symbol | Name | |

10^{−1} C | dC | decicoulomb | 10^{1} C | daC | decacoulomb | |

10^{−2} C | cC | centicoulomb | 10^{2} C | hC | hectocoulomb | |

10^{−3} C | mC | millicoulomb | 10^{3} C | kC | kilocoulomb | |

10^{−6} C | µC | microcoulomb | 10^{6} C | MC | megacoulomb | |

10^{−9} C | nC | nanocoulomb | 10^{9} C | GC | gigacoulomb | |

10^{−12} C | pC | picocoulomb | 10^{12} C | TC | teracoulomb | |

10^{−15} C | fC | femtocoulomb | 10^{15} C | PC | petacoulomb | |

10^{−18} C | aC | attocoulomb | 10^{18} C | EC | exacoulomb | |

10^{−21} C | zC | zeptocoulomb | 10^{21} C | ZC | zettacoulomb | |

10^{−24} C | yC | yoctocoulomb | 10^{24} C | YC | yottacoulomb | |

Common multiples are in bold face. |

See also Metric prefix.

- The magnitude of the electrical charge of one mole of elementary charges (approximately 6.022×10
^{23}, the Avogadro number) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday equals 96485.33212... coulombs.^{ [10] }In terms of the Avogadro constant (*N*_{A}), one coulomb is equal to approximately 1.036×10^{−5}mol ×*N*_{A}elementary charges. - A capacitor of one farad can hold one coulomb at a drop of one volt.
- One ampere hour equals 3600 C, hence 1 mA⋅h = 3.6 C.
- One statcoulomb (statC), the obsolete CGS electrostatic unit of charge (esu), is approximately 3.3356×10
^{−10}C or about one-third of a nanocoulomb.

- The charges in static electricity from rubbing materials together are typically a few microcoulombs.
^{ [11] } - The amount of charge that travels through a lightning bolt is typically around 15 C, although for large bolts this can be up to 350 C.
^{ [12] } - The amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about 5 kC = 5000 C ≈ 1400 mA⋅h.
^{ [13] } - A typical smartphone battery can hold 10,800 coulombs (3000 miliampere-hours) of electricity.

- Abcoulomb, a cgs unit of charge
- Ampère's circuital law
- Coulomb's law
- Electrostatics
- Elementary charge
- Faraday constant, the number of coulombs per mole

- ↑ 6.241509126(38)×10
^{18}is the reciprocal of the 2014 CODATA recommended value 1.6021766208(98)×10^{−19}for the elementary charge in coulomb. - ↑ "SI Brochure (2019)" (PDF).
*SI Brochure*. BIPM. p. 127. Retrieved May 23, 2019. - ↑ "SI Brochure, Appendix 1" (PDF). BIPM. p. 144.
- ↑ "SI brochure (2019)" (PDF).
*SI Brochure*. BIPM. p. 130. Retrieved May 23, 2019. - ↑ "SI brochure (2019)" (PDF).
*SI Brochure*. BIPM. p. 132. Retrieved May 23, 2019. - ↑ "2018 CODATA Value: elementary charge".
*The NIST Reference on Constants, Units, and Uncertainty*. NIST. 20 May 2019. Retrieved 2019-05-20. - ↑ 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 10^{9}C.G.S. units of resistance; the "volt" is approximately 10^{8}C.G.S. units of electromotive force; and the "farad" is approximately 1/10^{9}of the C.G.S. unit of capacity." - ↑ (Anon.) (September 24, 1881) "The Electrical Congress,"
*The Electrician*,**7**. - ↑ Donald Fenna,
*A Dictionary of Weights, Measures, and Units*, OUP (2002), 51f. - ↑ "2018 CODATA Value: Faraday constant".
*The NIST Reference on Constants, Units, and Uncertainty*. NIST. 20 May 2019. Retrieved 2019-05-20. - ↑ Martin Karl W. Pohl. "Physics: Principles with Applications" (PDF). DESY. Archived from the original (PDF) on 2011-07-18.
- ↑ Hasbrouck, Richard. Mitigating Lightning Hazards Archived 2013-10-05 at the Wayback Machine , Science & Technology Review May 1996. Retrieved on 2009-04-26.
- ↑
*How to do everything with digital photography – David Huss*, p. 23, at Google Books, "The capacity range of an AA battery is typically from 1100–2200 mAh."

The **ampere**, often shortened to **amp**, is the base unit of electric current in the International System of Units (SI). It is named after André-Marie Ampère (1775–1836), French mathematician and physicist, considered the father of electromagnetism.

In physics, an **electronvolt** is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules is equivalent to the numerical value of the charge of an electron in coulombs. Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value 1.602176634×10^{−19} J.

The **kilogram** is the base unit of mass in the International System of Units (SI), the metric system, having the unit symbol **kg**. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a **kilo** colloquially.

The **International System of Units** is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. It comprises a coherent system of units of measurement starting with seven base units, which are the second, metre, kilogram, ampere, kelvin, mole, and candela. The system allows for an unlimited number of additional units, called derived units, which can always be represented as products of powers of the base units. Twenty-two derived units have been provided with special names and symbols. The seven base units and the 22 derived units with special names and symbols may be used in combination to express other derived units, which are adopted to facilitate measurement of diverse quantities. The SI also provides twenty prefixes to the unit names and unit symbols that may be used when specifying power-of-ten multiples and sub-multiples of SI units. The SI is intended to be an evolving system; units and prefixes are created and unit definitions are modified through international agreement as the technology of measurement progresses and the precision of measurements improves.

The **SI base units** are the standard units of measurement defined by the International System of Units (SI) for the seven base quantities of what is now known as the International System of Quantities: they are notably a basic set from which all other SI units can be derived. The units and their physical quantities are the second for time, the metre for length, the kilogram for mass, the ampere for electric current, the kelvin for thermodynamic temperature, the mole for amount of substance, and the candela for luminous intensity. The SI base units are a fundamental part of modern metrology, and thus part of the foundation of modern science and technology.

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

The **Avogadro constant** (*N*_{A} or *L*) is the proportionality factor that relates the number of constituent particles (usually molecules, atoms or ions) in a sample with the amount of substance in that sample. Its SI unit is the reciprocal mole, and it is defined as *N*_{A} = 6.02214076×10^{23} mol^{−1}. It is named after the Italian scientist Amedeo Avogadro. Although this is called Avogadro's constant (or number), he is not the chemist who determined its value. Stanislao Cannizzaro explained this number four years after Avogadro's death while at the Karlsruhe Congress in 1860.

The **dalton** or **unified atomic mass unit** is a unit of mass widely used in physics and chemistry. It is defined as 1⁄12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. The **atomic mass constant**, denoted *m*_{u} is defined identically, giving *m*_{u} = *m*(^{12}C)/12 = 1 Da. A unit dalton is also approximately numerically equal to the molar mass of the same expressed in g / mol. Prior to the 2019 redefinition of the SI base units these were numerically identical by definition and are still treated as such for most purposes.

The **Faraday constant**, denoted by the symbol *F* and sometimes stylized as ℱ, is named after Michael Faraday. In chemistry and physics, this constant represents the magnitude of electric charge per mole of electrons. It has the currently accepted value

The **henry** is the SI derived unit of electrical inductance. If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self inductance of 1 henry. The unit is named after Joseph Henry (1797–1878), the American scientist who discovered electromagnetic induction independently of and at about the same time as Michael Faraday (1791–1867) in England.

The **farad** (symbol: **F**) is the SI derived unit of electrical capacitance, the ability of a body to store an electrical charge. It is named after the English physicist Michael Faraday (1791-1867). In SI base units 1 F = 1 kg^{−1}⋅m^{−2}⋅s^{4}⋅A^{2}.

The **elementary charge**, usually denoted by `e` or sometimes `q`_{e} is the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 `e`. This elementary charge is a fundamental physical constant. To avoid confusion over its sign, *e* is sometimes called the **elementary positive charge**.

The magnetic flux, represented by the symbol **Φ**, threading some contour or loop is defined as the magnetic field **B** multiplied by the loop area **S**, i.e. **Φ** = **B** ⋅ **S**. Both **B** and **S** can be arbitrary, meaning **Φ** can be as well. However, if one deals with the superconducting loop or a hole in a bulk superconductor, the magnetic flux threading such a hole/loop is actually quantized. The (superconducting) **magnetic flux quantum**Φ_{0} = *h*/(2*e*) ≈ 2.067833848...×10^{−15} Wb is a combination of fundamental physical constants: the Planck constant *h* and the electron charge *e*. Its value is, therefore, the same for any superconductor. The phenomenon of flux quantization was discovered experimentally by B. S. Deaver and W. M. Fairbank and, independently, by R. Doll and M. Näbauer, in 1961. The quantization of magnetic flux is closely related to the Little–Parks effect, but was predicted earlier by Fritz London in 1948 using a phenomenological model.

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**Vacuum permittivity**, commonly denoted ** ε_{0}** is the value of the absolute dielectric permittivity of classical vacuum. Alternatively it may be referred to as the permittivity of free space, the

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A **conventional electrical unit** is a unit of measurement in the field of electricity which is based on the so-called "conventional values" of the Josephson constant, the von Klitzing constant agreed by the International Committee for Weights and Measures (CIPM) in 1988, as well as Δ*ν*_{Cs} used to define the second. These units are very similar in scale to their corresponding SI units, but are not identical because of the different values used for the constants. They are distinguished from the corresponding SI units by setting the symbol in italic typeface and adding a subscript "90" – e.g., the conventional volt has the symbol *V*_{90} – as they came into international use on 1 January 1990.

The **International System of Electrical and Magnetic Units** is an obsolete system of units used for measuring electrical and magnetic quantities. It was proposed as a system of practical international units by unanimous recommendation at the International Electrical Congress, discussed at other Congresses, and finally adopted at the International Conference on Electric Units and Standards in London in 1908. It was rendered obsolete by the inclusion of electromagnetic units in the International System of Units (SI) at the 9th General Conference on Weights and Measures in 1948.

Effective 20 May 2019, the 144th anniversary of the Metre Convention, the SI base units were redefined in agreement with the International System of Quantities. In the redefinition, four of the seven SI base units – the kilogram, ampere, kelvin, and mole – were redefined by setting exact numerical values when expressed in SI units for the Planck constant, the elementary electric charge, the Boltzmann constant, and the Avogadro constant, respectively. The second, metre, and candela were already defined by physical constants and were not subject to correction to their definitions. The new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements. In November 2018, the 26th General Conference on Weights and Measures (CGPM) unanimously approved these changes, which the International Committee for Weights and Measures (CIPM) had proposed earlier that year after determining that previously agreed conditions for the change had been met. These conditions were satisfied by a series of experiments that measured the constants to high accuracy relative to the old SI definitions, and were the culmination of decades of research.

The scientific community examined several **alternative approaches to redefining the kilogram** before deciding on a redefinition of the SI base units in November 2018. Each approach had advantages and disadvantages.

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