The coulomb, symbol C, is the SI unit of electric charge, and is defined in terms of the ampere: 1 coulomb is the amount of electric charge (quantity of electricity) carried by a current of 1 ampere flowing for 1 second. It is also about 6.241506×10¹⁸ times the charge of an electron. It is named after Charles-Augustin de Coulomb (1736-1806).

Contents

1 Alternate definition 2 A wrong definition 3 SI electricity units 4 See also

Alternate definition

Since the values of the Josephson (CIPM (1988) Recommendation 1, PV 56; 19) and von Klitzing (CIPM (1988), Recommendation 2, PV 56; 20) constants have been given conventional values, it is possible to combine these values (K_J ≡ 4.835 979�10¹⁴ Hz/V and R_K ≡ 2.581 280 7�10⁴ Ω) to form an alternate (not yet official) definition of the coulomb. Very simply, a coulomb is then equal to exactly 6.241 509 629 152 65 � 10¹⁸ elementary charges.

A wrong definition

It is sometimes incorrectly said that a coulomb is defined as one mole of electrons (approximately 6.022×10²³, or Avogadro's number). This is completely wrong. One mole of electrons is known as a faraday. Just as the ampere and second were defined well before the electron's charge was known, the kilogram was defined well before the mass of the amu was known. Neither value has anything to do with the other. In terms of Avogadro's number (N_A), a coulomb is equal to approximately 1.036 × N_A × 10^-5 elementary charges.

SI electricity units

SI electromagnetism units edit  (http://www.wordiq.com/definition/Template:SI_electromagnetism_units)
Name	Symbol	Dimensions	Quantity
ampere (SI base unit)	A	A	Current
coulomb	C	A�s	Electric charge, Quantity of electricity
volt	V	J/C = kg�m2�s−3�A−1	Potential difference
ohm	Ω	V/A = kg�m2�s−3�A−2	Resistance, Impedance, Reactance
ohm metre	Ω�m	kg�m3�s−3�A−2	Resistivity
farad	F	C/V = kg−1�m−2�A2�s4	Capacitance
farad per metre	F/m	kg−1�m−3�A2�s4	Permittivity
reciprocal farad	F−1	kg1�m2�A−2�s−4	Elastance
siemens	S	Ω−1 = kg−1�m−2�s3�A2	Conductance, Admittance, Susceptance
siemens per metre	S/m	kg−1�m−3�s3�A2	Conductivity
weber	Wb	V�s = kg�m2�s−2�A−1	Magnetic flux
tesla	T	Wb/m2 = kg�s−2�A−1	Magnetic flux density
ampere per metre	A/m	m−1�A	magnetic induction
ampere-turns per weber	A/Wb	kg−1�m−2�s2�A2	Reluctance
henry	H	V�s/A = kg�m2�s−2�A−2	Inductance
henry per metre	H/m	kg�m�s−2�A−2	Permeability
(dimensionless)	-	-	Magnetic susceptibility

See also

• current (electricity)
• SI
• Faraday constant
• Coulomb's law

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