MadSci Network: Physics

Re: Is it 1 amp = 6.28 Billion Billion electrons per second?

Date: Wed Feb 23 13:00:59 2000
Posted By: Shel Randall, System Consultant
Area of science: Physics
ID: 950021243.Ph

It's too bad that schools have to continue to use outdated material. However, the nice thing about scientific constants and unit definitions is that they usually don't change. The number of known elements is not such a constant anymore than the number of known planets. We might choose to measure velocity in furlongs per fortnight, but we don't; the units remain the same whether we use them or not. Fortunately we do still use the ampere, defined as 1 coulomb of electricity per second.

The "ampere" is named for Andre Marie Ampere (1775-1836) (whose accomplishments in the field of electrodynamic theory are beyond the scope of this write-up). The International System of Units define an ampere as "the constant current that, when flowing in two parallel conductors one meter apart in a vacuum, will produce a force between the conductors of 2x10-7 newtons per meter of length." To produce this current, a certain number of electrons need to be moving through the conductors past a certain point in a certain amount of time. If a "second" is the time period, then we define a standard unit amount of electrons that pass a given point in this flow in one second; the International System of Units calls this number of electrons a "coulomb".

The "coulomb" is named for Charles Augustin de Coulomb (1736-1806), who, among other things, assisted the new French government at the time in devising a metric system of weights and measures (probably how he got this thing named after him, which just goes to show that it's as much who you know as what you know). A coulomb is a count of 6,241,507,648,655,549,400 (6.24x1018) electrons (give or take a few), the number of electrons that pass a given point in one second under the conditions described above. (Can you just see Chuck sitting there next to a pair of precisely constructed conductors counting over 6 quintillion electrons, one at a time?)

So, if there are 6.24x1018 electrons in a coulomb, then a single electron makes up about 1.602x10-19 coulombs, just for your information.

To answer your question, I'm fairly certain that the definitions of the units have not changed. (A study of the history of these units might be interesting.) And that being the case, I can say with some certainty that one coulomb still represents 6.28 billion billion electrons (though I cringe at the imprecision of the term "billion billion"), and so one ampere is still 6.28 billion billion electrons per second.

Note that I could have just answered the question "Yes." and been done with it, but I thought a more detailed answer was in order. :)

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