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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.
Force was redefined in the prequels as midichlorians multiplied by anger. Conveniently it's kept the same equation:
f = ma
Technically no. As noted above, the Ampere, not the Coulomb, is the fundamental unit. A Coulomb is an Ampere-second.
How about we change "At present, an ampere is defined as" to "Currently, an ampere is defined as"?
This is not entirely correct. Ampere is an SI base unit while Coulomb is a SI derived unit (defined as 1 C = 1 A s) - not the other way round.
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.
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
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
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