Check your comprehension

Check your comprehension

~ What are the obstacles to using an electric motor to lift an object having mass m in ordertodefine mass in terms of the amount of energy in the real world?

~ Which SI units does the watt balance method link?

~ Is it possible to achieve the desired accuracy with the best available techniques?

~ Why must all the procedures be performed in a vacuum?

~ What will the degree of agreement of results of the three laboratories engaged in developing watt balances method indicate?

Weighty Future

THE LATEST RESULTS from the work on the Avogadro constant and those from the NPL and NIST watt balances differ by more than one part in a million. Researchers must reconcile this discrepancy before a redefinition of the kilogram will be possible.

Redefinition in terms of the Avogadro constant or Planck’s constant will have widespread effects, reducing reported uncertainties associated with those constants. Moreover, if Planck's constant and the elementary electric charge are fixed (by combining, for example, watt balance and calculable capacitor measurements), many other important constants would also be fixed.

The International Committee for Weights and Measures has recommended that national measurement laboratories continue their efforts aimed at measuring the fundamental constants that support the redefinition process. Researchers hope that these steps will lead to new standards not only for the kilogram but the ampere, the kelvin and the mole by 2011.

Once the redefinition is complete, a few nations will build or maintain the equipment necessary for implementing the definition directly. Those that do not will have their standards calibrated using a consensus value for the kilogram derived from the laboratory work. Still, fears of damaging or contaminating a single master reference standard should fall away because comparisons between national standards and a working standard based on the new definition could be performed as needed. The new definition would allow authorities to adjust the world mass scale in tiny steps every so often to keep it free of drift and fully locked to the best – the latest consensus and independently confirmed – value of the SI unit of mass. Such a system would be robust and stable, allowing scientific and technological progress to continue unabated.

~ Which other important constants would be fixed after a redefinition of the kilogram?

~ Will fears of damaging or contaminating a single master reference standard remain after a redefinition of the kilogram?

Дата добавления: 2014-10-31