The coulomb (symbol: C) is the SI unit of electric charge. It is named after Charles-Augustin de Coulomb [1] (1736 to 1806).

Definition

1 coulomb is the amount of electric charge carried by a current of 1 ampere flowing for 1 second.

${\displaystyle C = A \cdot s}$

Explanation

The coulomb could in principle be defined in terms of the charge of an electron or elementary charge. Since the values of the Josephson constant [2] (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing constant [3] (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values (K_J ≡ 4.835 979¹⁴ Hz/V and R_K ≡ 2.581 280 7×10⁴Ω), it is possible to combine these values to form an alternative (not yet official) definition of the coulomb. A coulomb is then equal to exactly 6.241 509 629 152 65 x 10¹⁸ elementary charges. Combined with the current definition of the ampere, this proposed definition would make the kilogram a derived unit.

SI multiples

Multiple	Name	Symbol	Multiple	Name	Symbol
100	coulomb	C
101	decacoulomb	daC	10−1	decicoulomb	dC
102	hectocoulomb	hC	10−2	centicoulomb	cC
103	kilocoulomb	kC	10−3	millicoulomb	mC
106	megacoulomb	MC	10−6	microcoulomb	µC
109	gigacoulomb	GC	10−9	nanocoulomb	nC
1012	teracoulomb	TC	10−12	picocoulomb	pC
1015	petacoulomb	PC	10−15	femtocoulomb	fC
1018	exacoulomb	EC	10−18	attocoulomb	aC
1021	zettacoulomb	ZC	10−21	zeptocoulomb	zC

Conversions

• One mole of electrons (approximately 6.022 10²³, or Avogadro's number [4]) is known as a faraday (actually -1 faraday, since electrons are negatively charged). One faraday equals 96.485 341 5 kC (the Faraday constant [5]). In terms of Avogadro's number (N_A), one coulomb is equal to approximately 1.036 x N_A x 10⁻⁵ elementary charges.

• one ampere-hour = 3600 C

• The elementary charge is approximately 160.2176 zC.

• One statcoulomb (statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356 x 10⁻¹⁰C or about 1/3 nC.

See also

• Coulomb's law [6]
• Current (electricity)
• Faraday constant
• Quantity of electricity
• SI
• Ampere

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