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Ampere Could Be Redefined After Experiments Track Single Electrons Crossing Chip
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."
A kilogram is straightforwardly defined as 2.20462 pounds. Simple enough.
Because a few atoms of the slug can sublimate into the surrounding atmosphere, even at room temperature. And because a few atoms of the surrounding atmosphere can adhere to the slug. And yes, at the precision we're talking about here, it makes a difference.
I prefer rebel units. If you can't depend on Luke Skywalker for your calibrations, who can you trust?
The Ampere was only chosen as an SI fundamental unit because it was easier to measure than a Coulomb. To me, an Ampere will always be 1 Coulomb per second.
And since the electric charge is 1.602E-19 Coulombs, we can just invert that number to find the number of electric charges (ie, electrons) in a Coulomb.
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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.
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Force was redefined in the prequels as midichlorians multiplied by anger. Conveniently it's kept the same equation:
f = ma
How about we change "At present, an ampere is defined as" to "Currently, an ampere is defined as"?
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?
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.
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A duck.
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.
www.wavefront-av.com
I'll probably get down modded but it is not just the technologies but the basic definitions of the SI system are pretty fucked up.
There are numerous problems, the primary being:
* the seven SI base units are not independent
e.g. the Amp depends on the definition of the kilogram ?!?!
http://www1.bipm.org/en/si/si_constants.html#figure
Quoting Dr. Xavier with my emphasis added:
"If for instance, one had to change the definition of the Kg unit, we see that the fundamental units candela, mole, Amp and Kelvin would change as well. .. So one cannot say there are seven fundamental SI units if these units are not independent of each other. The other big fault is the obvious redundancy of units. Although not very well known to all of us, at least two of the seven base units of the SI system are officially known to be redundant, namely the mole and the candela. These two units have been dragging along, ending up in the SI system for no reason other than historic ones. "
* http://www.blazelabs.com/f-u-suconv.asp
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?
That approach is in fact one of the proposals for a replacement to the kilogram. The problem is counting 10^23 atoms of a material (and getting pure material to work with).
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It is kept in air, but under bell jars. Way more than you ever wanted to know here...
http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram
You have the right to remain sentient. If you give up the right to remain sentient, you will be elected to public office
Platinum and Iridium sublimate? Are you serious?
Sure it can. It just does it VERY slowly. The solid state is greatly preferred for these metals at room temperature, but at any temperature and pressure solid, liquid, and gas are all in equilibrium. When you're talking about thermodynamics and statistical mechanics, about the only absolute is zero, and that is a state that doesn't physically exist anywhere.
Then throw in quantum mechanics. There is probably some small but finite probability that I'll appear in your living room before I finish typ
The magnitude of many of the units comprising the SI system of measurement, including most of those used in the measurement of electricity and light, are highly dependent upon the stability of a 135-year-old, golf ball-size cylinder of metal stored in a vault in France.