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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."
"almost as much of an embarrassment"
You would have done better with the technologies at hand at the time how?
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.
It's hard to consistantly and accurately measure weight when the force of gravity constantly changes, add to the fact that there may be radioactive decay of trace elements, oxidation of metals, Dust/erosion, sublimation of trace components), it's easy to understand how using a physical object to consistantly measure a weight, would fluxuate. when your "constants" are actually "variables" it's really hard to nail down constants...
Wear... Even at a microscopic level the it can still suffer wear as a result of otherwise imperceptible movement and is also why it's designed as it is.
Since one of the most common SI units is based on however much this thing weights it's important that it be left as intact as possible.
http://en.wikipedia.org/wiki/Kilogram#Stability_of_the_international_prototype_kilogram
> K4 was originally delivered with an official mass of 1 kg75 g in 1889, but as of 1989 was officially calibrated at 1 kg106 g and ten years later was 1 kg116 g. Over a period of 110 years, K4 lost 41 g relative to the IPK.
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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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.
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.
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
Force was redefined in the prequels as midichlorians multiplied by anger. Conveniently it's kept the same equation:
f = ma
Charge is quantized. This has been known since Millikan. You can't ever arrive at an electron-and-a-half of charge (though you can, in theory, get a third or two thirds, but not naturally in nature).
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 . . .
How about we change "At present, an ampere is defined as" to "Currently, an ampere is defined as"?
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. The problem of how to properly clean the things has been going on for years.
K4 was originally delivered with an official mass of 1 kg75ug in 1889, but as of 1989 was officially calibrated at 1 kg106ug and ten years later was 1 kg116ug. Over a period of 110 years, K4 lost 41ug relative to the IPK.
Your mu's got eaten by slashdot. Those should all be micrograms. Naturally μ doesn't work.
Tiller's Rule: Never use a word in written form that you've only heard and never read. You will end up looking foolish.
6, if you regularly read Facebook for math tips.
Is it just my observation, or are there way too many stupid people in the world?
>Unlike an atomic clock where you can precisely define the unit of time in wavelengths of whatevers, there's no way to define the kilogram in a more specific way.
Really? Seems to me it would be easy enough to say 1g = 1/12 the mass of one mole of Carbon-12, or your element of choice - preferably something common, stable, and monoisotopic for convenience (http://en.wikipedia.org/wiki/Monoisotopic_element). Obviously we'll want to choose our atom carefully since per-nucleon mass is different fro every element. Maybe iron since it has the minimum per-nucleon energy, meaning all other nucleons will have a mass slightly >1, or perhaps hydrogen-1 as the most abundant element, and the closest we can get to the mass of a free proton. Of course that doesn't really scale all that well for practical applications, nobody is actually going to want to count out the 602,214,130,000,000,000 atoms necessary to get to even the microgram range using modern technology, but there's no reason we couldn't define the unit in such terms, and then continue using carefully protected metal slugs as "best approximation" reference masses. Heck, perhaps we could even use a low-speed particle accelerator to embed a precise number of atoms into a reference mass to create a specific mass-delta.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
http://www.youtube.com/watch?v=ZMByI4s-D-Y
This youtube video answered most of my questions about the kilogram.
Bearded Dragon
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
It's not iridium coated, it's iridium-alloyed - adds hardness.
The problem here is declaring something involving atoms impossible, and well, on the atomic scale nothing is. It sits in lit room at room temperature - there is a whole hell of a lot of EM falling on it, and so every now and again somewhere on it you might exceed the work function of the metal and sputter it. You've also got to deal with not just air sticking to it, but being absorbed into it's bulk - atmospheric humidity would be a big concern since water sticks to everything and is just about impossible to get rid of. Then you've got hydrogen and helium diffusion as well.
Why name a unit after them and obfuscate the meaning of the unit?
Why is a second called a second? Why is a (kilo)gram called a (kilo)gram? Why is a mole called a mole?
I have no idea about any of those, but I don't have any trouble remembering what they are the units of.
What's so confusing about re-using a scientist's name? Would you prefer "time unit" or "mass unit"?
systemd is Roko's Basilisk.
That's great in theory, but in practice, there is a master kilogram and several reference kilograms actually used for standardizing measurement. They keep drifting apart somehow.
That somehow is either the evil machinations of the faery world or it is sublimation and adhesion.
And never the two shall meet . . .
Except over Mars.
... fleetingly...
XML is a known as a key material required to create SMD: Software of Mass Destruction
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.
In classical statistical mechanics, you can have a solid that has a low enough, but non-zero temperature such that the change of any given atom having enough energy to leave the surface has effectively zero probability on a relevant timescale.
That "effectively zero probability" means that it sublimes. It just does it REALLY slowly. And that is if you want to keep the standard at a near-absolute-zero temperatures for decades. That creates a whole different set of problems. Can you weigh it as accurately at those temperatures? If you have to warm and cool it, does the mass change due to damage during expansion/etc? Can you maintain it at that temperature without any contamination (if it is that cold than any molecule of gas that leaks in will condense or solidify).
That's the whole problem with the kilogram standard. They're probably managing it as best as they can already, but it will never be perfect, and they're well past the point of diminishing returns so anytime you want to consider any improvement you have to factor in all of physics.