The unit of current - the Ampere |
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Historically attempts were made to define the Coulomb by literally counting silver atoms deposited by a current on an electrode (One atom per electron.) The Ampere was then defined as a current of one Coulomb per second. Uncertainty as to the weight of the silver atom limited the accuracy of the determination. The solution was to define the Ampere in terms of the force between two parallel current carrying wires. A current of one Ampere flows in parallel wires that, when placed one meter apart, have a force per meter acting between them of 2 by ten to the minus seven Newtons per meter. With this definition the Coulomb is now defined as that charge delivered per second by a current of one Ampere. |
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