Coulomb (unit)
Generated by GPT-5-miniExpansion Funnel Raw 58 → Dedup 9 → NER 4 → Enqueued 1
| Coulomb (unit) | |
|---|---|
.png) VectorVoyager · CC BY-SA 4.0 · source | |
| Name | Coulomb |
| Quantity | Electric charge |
| Si unit of | Electric charge |
| Derived from | Ampere × second |
| Named after | Charles-Augustin de Coulomb |
Coulomb (unit) is the SI derived unit of electric charge, defined as the amount of charge transported by a constant current of one ampere in one second. It functions within the International System of Units administered by organizations such as the International Bureau of Weights and Measures and relates directly to units used in electromagnetism, metrology, and electrical engineering. The unit's adoption and ongoing use connect to historical figures and institutions in physics, standardization, and industrial development.
Definition and SI status
The unit is defined by the SI as one ampere-second, linking it to the SI base unit ampere as maintained by the International System of Units and interpreted by the Comité International des Poids et Mesures. Under the 2019 redefinition of SI base units driven by the Planck constant and other fundamental constants, the ampere (and therefore the coulomb) is realized via fixed numerical values of the elementary charge and experimental implementations by national laboratories such as the National Institute of Standards and Technology, the Physikalisch-Technische Bundesanstalt, and the National Physical Laboratory (United Kingdom). In engineering practice the coulomb is used alongside units such as the volt, ohm, farad, and watt for circuit analysis and energy calculations.
Historical development and etymology
The unit is named in honor of Charles-Augustin de Coulomb, whose 18th-century torsion balance experiments on electrostatic forces influenced the formulation of Coulomb's law and the quantitative study of charge. The naming followed proposals by scientific bodies including the Bureau International des Poids et Mesures and national academies such as the Académie des sciences (France) and the Royal Society. Adoption of the name paralleled developments in the study of electricity by figures like Benjamin Franklin, Alessandro Volta, Michael Faraday, Georg Ohm, and James Clerk Maxwell, and institutional standardization driven by the International Electrotechnical Commission and the International Union of Pure and Applied Physics.
Relationship to other electrical units and constants
The coulomb relates to electromagnetic units and constants: 1 C = 1 A·s connects it to the ampere and the second; in Coulomb's law the Coulomb constant (k_e) is expressible through the vacuum permittivity ε0 and the Planck constant and speed of light via SI conventions. Charge quantization ties the coulomb to the elementary charge e, where e ≈ 1.602176634×10^−19 C, linking to experiments by laboratories such as the CERN and measurements referenced by the CODATA. In circuit theory the coulomb relates to capacitance: 1 farad = 1 C/V where volt and ampere appear in Ohm’s law with resistance measured in ohm.
Measurement methods and realization
Realization of the coulomb relies on realizing the ampere and second. Modern implementations use single-electron transport devices, quantum standards like the Josephson effect for voltage and the quantum Hall effect for resistance, and electron-counting experiments using electron beam ionization and single-electron pumps developed at institutions such as the National Research Council (Canada) and PTB. Current balance experiments historically based on magnetic force between conductors trace to work by André-Marie Ampère and were refined by metrology institutes including BIPM and NIST. Charge measurement techniques include coulometry used in electrochemistry laboratories at universities such as Massachusetts Institute of Technology and University of Cambridge, and electrometers developed by companies like Keithley Instruments and research groups at Royal Holloway, University of London.
Applications and usage examples
Coulombs are used to specify battery capacity (ampere-hours converted to coulombs) in manufacturers such as Tesla, Inc. or Panasonic Corporation, to quantify charge transfer in electroplating by firms in the electrochemical industry and to report charge in particle physics experiments at Fermilab and SLAC National Accelerator Laboratory. In electronics, designers at companies like Intel Corporation and Samsung Electronics estimate charge storage in capacitors for microprocessors; in telecommunications corporations such as AT&T and Ericsson evaluate signal charge in analog front-ends. Coulomb-counting is employed in state-of-charge algorithms in electric vehicle systems by manufacturers like Nissan and General Motors and in instrumentation for spacecraft by agencies including NASA and the European Space Agency.
Conversion and dimensional analysis
Dimensionally, the coulomb is represented as A·s in SI base units and can be expressed in terms of mechanical units via electromagnetic constants: charge can be related to mass, length, and time using ε0 and μ0 and fundamental constants such as the Planck constant and the elementary charge. Conversions: 1 C = 1 A·s; 1 ampere-hour = 3600 C; in CGS electrostatic units 1 statcoulomb ≈ 3.33564×10^−10 C, with historical context involving the centimeter–gram–second system and its electromagnetic subsystems. Dimensional analysis in electromagnetic theory often references Maxwell’s equations and constants standardized by bodies like the International Electrotechnical Commission.