Ampere to get rational redefinition

Single-electron flow measured in bid to overhaul SI base unit.

Physicists have tracked electrons crossing a semiconductor chip one at a time — an experiment that should at last enable a rational definition of the ampere, the unit of electrical current.

At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one metre apart, such that the wires attract each other with a force of 2 × 10−7 newtons per metre of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy — almost as much of an embarrassment as the definition of the kilogram, which relies on the fluctuating mass of a 125-year-old platinum-and-iridium cylinder stored at the International Bureau of Weights and Measures (BIPM) in Paris.

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ananyo writes

“Physicists have tracked electrons crossing a semiconductor chip one at a time — an experiment that should at last enable a rational definition of the ampere, the unit of electrical current. At present, an ampere is defined as the amount of charge flowing per second through two infinitely long wires one meter apart, such that the wires attract each other with a force of 2×10^-7 newtons per meter of length. That definition, adopted in 1948 and based on a thought experiment that can at best be approximated in the laboratory, is clumsy — almost as much of an embarrassment as the definition of the kilogram, which relies on the fluctuating mass of a 125-year-old platinum-and-iridium cylinder stored at the International Bureau of Weights and Measures in Paris. The new approach, described in a paper posted onto the arXiv server on 19 December, would redefine the amp on the basis of e, a physical constant representing the charge of an electron.”

I always learned it was 6.25 × 10^18 electrons past given point per second think it were.

These days, being old and all, I say it is what you get when you put one Volt across one Ohm, saves falling into the quantum vacuum.

More precision.

“..charge passing a point in an electric circuit per unit time, with 6.241×10^18 electrons (or one coulomb) per second constituting one ampere…”

http://en.wikipedia.org/wiki/Ampere

http://en.wikipedia.org/wiki/Ampere

Ampère’s force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ampere, which states that it is “the constant current that will produce an attractive force of 2 × 10–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum”.

The SI unit of charge, the coulomb, “is the quantity of electricity carried in 1 second by a current of 1 ampere”. Conversely, a current of one ampere is one coulomb of charge going past a given point per second