Coulomb — SI unit of electric charge
The coulomb (C) is the SI unit of electric charge. Defined as the charge carried by a current of one ampere in one second, it links microscopic electron charge to macroscopic electrical measurements.
Overview: The coulomb (symbol C) is the International System of Units (SI) measurement for electric charge. It quantifies the amount of electric charge present or transferred and serves as the bridge between microscopic particle charge and practical electrical engineering. For the general concept of charge see electric charge.
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Definition and basic relation
By definition, one coulomb is the amount of charge transported by a steady electric current of one ampere flowing for one second. In symbolic form: 1 C = 1 A × 1 s. This relationship makes the coulomb a derived SI unit that is directly tied to the ampere and the second, allowing laboratory and industrial measurements of charge to be expressed in convenient macroscopic terms.
Characteristics and microscopic meaning
Electric charge is carried in conductors primarily by electrons. Each electron carries one elementary negative charge, so a coulomb corresponds to a very large number of electrons — about 6.24 × 1018 elementary charges. Because the elementary charge provides the fundamental unit of charge for stable particles, the coulomb is effectively a convenient aggregation of that smallest practical unit.
History and name
The unit is named after the 18th-century French physicist Charles‑Augustin de Coulomb, whose experimental and theoretical work on force between electric charges and on torsion balances laid foundations for electrostatics; see more on Charles‑Augustin de Coulomb. The modern SI definition links the coulomb to the ampere and second so that electrical measurements are reproducible and internationally consistent.
Uses, examples, and importance
The coulomb is used across physics and engineering whenever charge quantities are relevant. Examples include the charge stored by capacitors (specified in coulombs or farads when combined with voltage), the total charge transferred in electrochemical reactions, and charge balance calculations in electronics. For instance, a lamp drawing a steady current of 1 A will transfer 1 C of charge each second through its filament. For background on electrons as charge carriers see electron.
Practical notes and related concepts
- Measurement: Charge can be measured by integrating current over time (Q = ∫ I dt), reflecting the 1 A × 1 s definition.
- Relation to other laws: Coulomb's law (named after the same scientist) uses charges measured in coulombs when calculating electrostatic force between point charges.
- Unit conversions: Millcoulombs (mC) and microcoulombs (µC) are commonly used in electronics for smaller charge amounts.
For authoritative technical definitions and standards related to the coulomb and linked SI units consult standard references and national metrology institutes; more information can be found via general unit reference pages such as electric charge and unit definitions at recognized resources ampere and second. Additional historical and biographical context is available at sources covering Coulomb and fundamental particle properties like the electron.
Definition
The definition of the units coulomb and ampere is based on the elementary charge, which was defined as exactly 
has been established, see International System of Units.
Historical
In 1861, the two English electrical engineers Josiah Latimer Clark and Charles Tilston Bright proposed the farad as the unit for electric charge in honour of the English physicist Michael Faraday. In 1881, however, the International Electricity Congress established the coulomb as the unit for electric charge and the farad as the unit for electric capacitance.
The current definition of the coulomb by defining the elementary charge was adopted at the 26th General Conference on Weights and Measures on November 16, 2018, and became effective May 20, 2019. Previously, the ampere had been defined by the Lorentz force of the electric current, and the coulomb as an ampere-second.
Questions and answers
Q: What is a coulomb?
A: A coulomb is a unit of electric charge.
Q: Who is Charles-Augustin de Coulomb?
A: Charles-Augustin de Coulomb was a scientist who studied electric charge in the late 1700s. The coulomb is named after him.
Q: What is current in an electric circuit?
A: Current in an electric circuit is the movement of electric charge.
Q: If a flashlight bulb has a current of one ampere, how many coulombs of charge will pass through it every second?
A: If a flashlight bulb has a current of one ampere, one coulomb of charge will pass through it every second.
Q: What particle carries the charge that moves in an electric wire?
A: The particle that carries the charge that moves in an electric wire is the electron.
Q: What is the smallest electric charge found in a stable particle?
A: The smallest electric charge found in a stable particle is the elementary charge.
Q: How many elementary charges are there in a coulomb?
A: There are 6,241,509,629,152,650,000 elementary charges in a coulomb.
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AlegsaOnline.com Coulomb — SI unit of electric charge Leandro Alegsa
URL: https://en.alegsaonline.com/art/23425