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

Posted
by
timothy

from the micro-management dept.

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."
## Condescend much? (Score:3, Interesting)

You would have done better with the technologies at hand at the time how?

## Bah, I say (Score:3, Interesting)

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.

## Re:fluctuating weight of KG? (Score:2, Interesting)

That's part of the problem. Scientists aren't exactly sure. Shortly after it was made, several copies were made in 1889 that were verified to be the exact same mass. Over the years, the mass of the original and its copies have slightly drifted. The copies appear to have grown heavier, while the original has grown lighter. But even that's hard to determine for sure, since we can only be sure of the *difference* of the masses, not their absolute mass, because absolute mass is defined in terms of these kilogram masses in the first place.

It's theorized that air molecules may be attaching to the copies (they are also kept in a vacuum environment, but no vacuum is perfect), but if that's the case, why hasn't it happened to the original? The difference is only 50 ug, but that comes out to be 0.005%, which is huge for scientific applications. All of this means that they need a better quantitative standard for the kilogram.

## Re:Condescend much? (Score:5, Interesting)

I'll probably get down modded but it is not just the

technologiesbut thebasicdefinitionsof the SI system are pretty fucked up.There are

numerousproblems, the primary being:* the seven SI base units are

not independente.g. the Amp depends on the definition of the kilogram ?!?!

http://www1.bipm.org/en/si/si_constants.html#figure [bipm.org]

Quoting Dr. Xavier with my emphasis added:

"If for instance, .. 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

one had to change the definition of the Kg unit, we see thatthe fundamental units candela, mole, Amp and Kelvin would change as well.moleand thecandela.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 [blazelabs.com]