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Science

Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip 299

Posted by timothy
from the micro-management dept.
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."
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Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip

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  • by bobbied (2522392) on Tuesday January 14, 2014 @01:13PM (#45953881)

    The fine article is incorrect. How an Ampere is defined does not change.

    What may change is how you can measure current in the lab using other known standards because it's really hard to count electrons. Or perhaps the way a Coulomb is defined may change but the Ampere will not change.

    One Ampere will remain defined as One Coulomb per second.

  • by mmell (832646) <mike.mell@gmail.com> on Tuesday January 14, 2014 @01:28PM (#45954167)
    Well, Imperial units are binary (1/2", 1/4", 1/8" tools, for example). Twelve inches in a foot divides evenly by two, three, four, six. Thirty-six inches in a yard has a lot of factors too. 5,280 feet in a mile seems arbitrary until you start counting the factors. Three hundred sixty degrees in a circle can evenly be divided by 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18... - tried that with radians lately? One hundred eighty degrees separate water freezing from water boiling - 180, another composite number with lots of factors. If you're an engineer, there's a lot to be said for Imperial or SAE units - they sure make a lot of the math easier.

    On the other hand, Metric is decimal. Last time I checked, everyone had ten fingers. We count base ten. Computers may be great at binary, but most of us do arithmetic for our daily tasks at base ten.

    Binary (Imperial) has its place. Decimal (Metric) has its place. And never the two shall meet . . .

  • by Minwee (522556) <dcr@neverwhen.org> on Tuesday January 14, 2014 @01:36PM (#45954281) Homepage

    Fucking genius! If only it were iron it would be corroding, but it's platinum and irridium. Corrosion is not a big factor. Forgetting to dust it would alter the mass more.

    Actually, remembering to dust it is what causes its mass to change [wired.com]. The problem of how to properly clean the things has been going on for years.

  • by Immerman (2627577) on Tuesday January 14, 2014 @01:43PM (#45954415)

    Sure, the same way they "weigh" things in freefall - measuring the radial forces necessary to keep it moving in a fixed circular path at a given speed. You can even vary the speed to get multiple measurements to reduce error. That may be as simple as a scale in a centrifuge, but does not depend on any way on potentially fluctuating gravitational field. It also incidentally directly measures inertial mass, rather than gravitational mass, which *apparently* is always present in precisely proportional amounts, but which we currently have no accepted theoretical reason to believe is a fundamental equivalence.

  • by Phreakiture (547094) on Tuesday January 14, 2014 @01:47PM (#45954499) Homepage

    Except now all you have is a ratio of two masses, rather than an absolute quantity. What exactly would you balance the kilogram reference against?

    You would use it to callibrate another mass as being a kilogram. I know this is kind of a circular problem, but that's really why the fluctuating mass is troubling, because that's supposed to be the stable benchmark, and it has proven not to be so stable.

  • by stdarg (456557) on Tuesday January 14, 2014 @02:40PM (#45955603)

    What's wrong with fixing Avogadro's number at something like 6.022 * 10^23 instead of defining it as the number of atoms of blah in blah, then saying a kilogram is 1/12 of the mass of Avogadro's number of Carbon 12 atoms. I'm sure that's been floated.. is the problem the arbitrariness of the number?

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