# Coulomb

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The coulomb (symbol: C) is the SI derived unit of electric charge, and is approximately equal to the charge of 6.24151×1018 protons or -6.24151×1018 electrons.[citation needed] It is named after Charles-Augustin de Coulomb.

## Contents

### Definition

One coulomb is the amount of electric charge transported in one second by a constant current of one ampere.[1][2][3]

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:

### Explanation

In principle, the coulomb could be defined in terms of the charge of a proton or elementary charge. Since the values of the Josephson [4] constants have been given conventional values (KJ ≡ 4.835 979×1014 Hz/V and RK ≡ 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.