Feeds

On the hunt for a new ampere

Counting charge one electron at a time

Intelligent flash storage arrays

While there's been lots of attention paid to the search for a new kilogram, another of the SI system's fundamental units of measurement is under examination: the ampere.

Along with the kilogram, metre, second, Kelvin, mole and candela, the ampere is one of the fundamental yardsticks used to measure the world around us. And, like the kilo, the ampere is suffering from the incredible accuracy of modern scientific instruments: its value differs ever so slightly under different measurement conditions.

In a much older world, the amp was measured in terms of vast numbers of electrons passing through a wire. One coulomb per second equals one amp. That, however, equates to an awful lot of electrons passing a point, and isn't particularly accurate in today's world, where you can create stop-motion movies with single atoms.

To get a more stable ampere, the Conférence Générale des Poids et Mesures proposes that the unit be defined in terms of electron charge. For example, a single electron pump, or SEP to its friends, can emit single electrons at a controllable rate by dropping them onto quantum dots.

However, metallic SEPs don't pump electrons fast enough to provide a usable ampere, so scientists from the National Physical Laboratory and the University of Cambridge have constructed one out of graphene, and are putting it forward as their suggested “SI ammeter”.

As their paper in Nature (abstract here) explains, the UK scientists believe their graphene-based SEP is accurate at the gigahertz range, which is sufficient to provide a new physical basis for the ampere.

However, in a demonstration of the Fundamental Interconnectedness of All Things*, regardless of what technique is eventually used to measure the ampere, it'll have to wait until the new definition of the kilogram is settled – because that will also nail down the SI value for electronic charge, on which the ampere will be based. ®

*Thanks to Douglas Adams ®

Update: a reader has sent The Register the following comment, which is worth reproducing:

"The ampere is not (and never has been) defined as the number of electrons passing a given point (that's a definition of the coulomb, a derived unit). All base units must be defined in terms of mass, length and time and here's the ampere: The current flowing in two rectilinear conductors of negligible cross-section 1 metre apart in vacuuo that produces a force of 2*10^-7 Newtons between them. There are issues with this due to measurement accuracy and the desire for a new definition has been desirable for some years."

Our thanks. ®

Choosing a cloud hosting partner with confidence

More from The Register

next story
SECRET U.S. 'SPACE WARPLANE' set to return from SPY MISSION
Robot minishuttle X-37B returns after almost 2 years in orbit
LOHAN crash lands on CNN
Overflies Die Welt en route to lively US news vid
No sail: NASA spikes Sunjammer
'Solar sail' demonstrator project binned
Experts brand LOHAN's squeaky-clean box
Phytosanitary treatment renders Vulture 2 crate fit for export
You can crunch it all you like, but the answer is NOT always in the data
Hear that, 'data journalists'? Our analytics prof holds forth
Carry On Cosmonaut: Willful Child is a poor taste Star Trek parody
Cringeworthy, crude and crass jokes abound in Steven Erikson’s sci-fi debut
Origins of SEXUAL INTERCOURSE fished out of SCOTTISH LAKE
Fossil find proves it first happened 385 million years ago
America's super-secret X-37B plane returns to Earth after nearly TWO YEARS aloft
674 days in space for US Air Force's mystery orbital vehicle
prev story

Whitepapers

Forging a new future with identity relationship management
Learn about ForgeRock's next generation IRM platform and how it is designed to empower CEOS's and enterprises to engage with consumers.
Why cloud backup?
Combining the latest advancements in disk-based backup with secure, integrated, cloud technologies offer organizations fast and assured recovery of their critical enterprise data.
Win a year’s supply of chocolate
There is no techie angle to this competition so we're not going to pretend there is, but everyone loves chocolate so who cares.
High Performance for All
While HPC is not new, it has traditionally been seen as a specialist area – is it now geared up to meet more mainstream requirements?
Intelligent flash storage arrays
Tegile Intelligent Storage Arrays with IntelliFlash helps IT boost storage utilization and effciency while delivering unmatched storage savings and performance.