Coulomb

For other uses, see Coulomb (disambiguation).

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	1 A s
CGS units	2997924580 statC
Atomic units	6.242×1018 e

The coulomb (symbol: C) is the SI derived unit of electric charge, transported by a steady current of one ampere in one second.

$1\mathrm {C} =1\mathrm {A} \cdot 1\mathrm {s}$

One coulomb is also the amount of excess charge on the positive side of a capacitance of one farad charged to a potential difference of one volt:

$1\mathrm {C} =1\mathrm {F} \cdot 1\mathrm {V}$

Name

The unit is named after Charles-Augustin de Coulomb. 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.

Explanation

The magnitude of an elementary charge, the charge of a proton or electron, is approximately 1.602176487(40)×10⁻¹⁹ coulombs. In principle, the coulomb could be defined in terms of the elementary charge. Since the values of the Josephson constants have been given conventional values (K_J ≡ 4.835 979×10¹⁴ Hz/V and R_K ≡ 2.581 280 7×10⁴ Ω), 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 65×10¹⁸ positive elementary charges. Combined with the present definition of the ampere, this proposed definition would make the kilogram a derived unit.

In everyday situations, positive and negative charges are usually balanced out. According to Coulomb's Law, two point charges of +1 C, one meter apart, would experience a repulsive force of 9×10⁹ N, a force roughly equal to the weight of 900,000 metric tons of mass.

SI prefixes

SI multiples of coulomb (C)

Submultiples			Multiples
Value	SI symbol	Name	Value	SI symbol	Name
10−1 C	dC	decicoulomb	101 C	daC	decacoulomb
10−2 C	cC	centicoulomb	102 C	hC	hectocoulomb
10−3 C	mC	millicoulomb	103 C	kC	kilocoulomb
10−6 C	μC	microcoulomb	106 C	MC	megacoulomb
10−9 C	nC	nanocoulomb	109 C	GC	gigacoulomb
10−12 C	pC	picocoulomb	1012 C	TC	teracoulomb
10−15 C	fC	femtocoulomb	1015 C	PC	petacoulomb
10−18 C	aC	attocoulomb	1018 C	EC	exacoulomb
10−21 C	zC	not used	1021 C	ZC	zettacoulomb
10−24 C	yC	not used	1024 C	YC	yottacoulomb
10−27 C	rC	rontocoulomb	1027 C	RC	ronnacoulomb
10−30 C	qC	quectocoulomb	1030 C	QC	quettacoulomb
Common multiples are in bold face.

See also SI prefix.

Conversions

• The magnitude of the electrical charge of one mole of protons (approximately 6.022×10²³, or Avogadro's number) is known as the Faraday constant or a faraday. One faraday is equal to 96485.3399 coulombs. In terms of Avogadro's number (N_A), one coulomb is equal to approximately 1.036 × N_A ×10⁻⁵ elementary charges.
• one ampere-hour = 3600 C, one mAh = 3.6 C
• The elementary charge is 1.602176487×10⁻¹⁹ C
• One statcoulomb (statC), the CGS electrostatic unit of charge (esu), is approximately 3.3356×10⁻¹⁰ C or about 1/3 nC.
• One coulomb is the amount of electrical charge in 6.241506×10¹⁸ protons, or equivalently, negative one (-1) coulomb is the electrical charge of 6.241506×10¹⁸ electrons.

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