Coulomb
{{#invoke:Hatnote|hatnote}} Template:Infobox Unit The coulomb (named after Charles-Augustin de Coulomb, unit symbol: C) is a fundamental unit of electrical charge, and is also the SI derived unit of electric charge (symbol: Q or q). It is equal in magnitude (absolute value) to the charge of approximately 6.241Template:E electrons, but has the opposite sign.
Its SI definition is the charge transported by a constant current of one ampere in one second:
One coulomb is also the amount of excess charge on a capacitor of one farad charged to a potential difference of one volt:
Name and notation
Definition
In the SI system, the coulomb is defined in terms of the ampere and second: 1 C = 1 A × 1 s.[2] The second is defined in terms of a frequency which is naturally emitted by caesium atoms.[3] The ampere is defined using Ampère's force law;[4] the definition relies in part on the mass of the international prototype kilogram, a metal cylinder housed in France.[5] In practice, the watt balance is used to measure amperes with the highest possible accuracy.[5]
Since the charge of one electron is known to be about −Template:Physconst −1 C can also be considered to be the charge of roughly Template:Gaps (or +1 C the charge of that many positrons or protons), where the number is the reciprocal of Template:Gaps.
SI prefixes
Template:SI multiples See also SI prefix.
Conversions
- The magnitude of the electrical charge of one mole of elementary charges (approximately 6.022Template:E, or Avogadro's number) is known as a faraday unit of charge (closely related to the Faraday constant). One faraday equals Template:Gaps. In terms of Avogadro's number (NA), one coulomb is equal to approximately 1.036 × NATemplate:E elementary charges.
- One ampere-hour = 3600 C, 1 mA⋅h = 3.6 C.
- The elementary charge is Template:Physconst
- One statcoulomb (statC), the obsolete CGS electrostatic unit of charge (esu), is approximately 3.3356Template:E C or about one-third of a nanocoulomb.
- One coulomb is the magnitude (absolute value) of electrical charge in Template:Gaps protons or electrons.[6]
Relation to elementary charge
The elementary charge, the charge of a proton (equivalently, the negative of the charge of an electron), is approximately Template:Physconst. In SI, the elementary charge in coulombs is an approximate value: no experiment can be infinitely accurate. However, in other unit systems, the elementary charge has an exact value by definition, and other charges are ultimately measured relative to the elementary charge.[7] For example, in conventional electrical units, the values of the Josephson constant KJ and von Klitzing constant RK are exact defined values (written KJ-90 and RK-90), and it follows that the elementary charge e =2/(KJRK) is also an exact defined value in this unit system.[7] Specifically, e90 = (2Template:E)/(Template:Gaps × Template:Gaps) C exactly.[7] SI itself may someday change its definitions in a similar way.[7] For example, one possible proposed redefinition is "the ampere...is [defined] such that the value of the elementary charge e (charge on a proton) is exactly Template:Gaps coulombs",[8] (in which the numeric value is the 2006 CODATA recommended value, since superseded). This proposal is not yet accepted as part of the SI; the SI definitions are unlikely to change until at least 2015.[9]
In everyday terms
- The charges in static electricity from rubbing materials together are typically a few microcoulombs.[10]
- The amount of charge that travels through a lightning bolt is typically around 15 C, although large bolts can be up to 350 C.[11]
- The amount of charge that travels through a typical alkaline AA battery from being fully charged to discharged is about 5 kC = 5000 C ≈ 1.4 A⋅h.[12]
- According to Coulomb's law, two negative point charges of Template:Val, placed one meter apart, would experience a repulsive force of Template:Val, a force roughly equal to the weight of Template:Gaps metric tons of mass on the surface of the Earth.
- The hydraulic analogy uses everyday terms to illustrate movement of charge and the transfer of energy. The analogy equates charge to a volume of water, and voltage to pressure. One coulomb equals (the negative of) the charge of Template:Val. The amount of energy transferred by the flow of 1 coulomb can vary; for example, 300 times fewer electrons flow through a lightning bolt than through an AA battery, but the total energy transferred by the flow of the lightning's electrons is 300 million times greater.
See also
- Abcoulomb, a cgs unit of charge
- Ampère's circuital law
- Coulomb's law
- Electrostatics
- Elementary charge
- Faraday (unit), an obsolete unit
- Quantity of electricity
Notes and references
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ 5.0 5.1 Template:Cite web
- ↑ Template:Gaps is the reciprocal of the 2010 CODATA recommended value Template:Gaps for the elementary charge in coulomb.
- ↑ 7.0 7.1 7.2 7.3 Template:Cite doi
- ↑ Report of the CCU to the 23rd CGPM
- ↑ Template:Cite web
- ↑ Template:Cite web
- ↑ Hasbrouck, Richard. Mitigating Lightning Hazards, Science & Technology Review May 1996. Retrieved on 2009-04-26.
- ↑ Template:Google books, "The capacity range of an AA battery is typically from 1100–2200 mAh."