Redefinition of Kilogram, Ampere, Kelvin, Mole comes into force

Redefinition of Kilogram, Ampere, Kelvin, Mole comes into force

Agency News

New Delhi 20 May: Four units of the international system of units ( SI) - kilogram, ampere, kelvin and mole - have been redefined today as 101 countries world wide, including India, have given up artifacts based measure to adopt fundamental physical constants based measures to redefine these units.

In a function held here at CSIR-National Physical Laboratory on World Metrology Day on Monday, former BARC director Dr. R Chidambaram introduced revised SI units. It was introduced in 60 permanent member countries and 41 allied countries of International Organization of Legal Metrology simultaneously.

"Its a historic day. We now confirm our self to the international units today,''Dr. Shekhar C Mande, Director General CSIR, said. There are seven basic SI units - kilogram, metre, second, ampere, Kelvin, Mole and candela. Out of these, three units- metre, second and candela - are already based on fundamental physical constants.
"By adopting new definitions and re-calibrating physical scales accordingly, perfection in measurement will improve. This will bring accuracy in scientific experiments and benefit common man as well. A slight variation may not affect when you are buying a kg of ration, but it will certainly matter when you are buying gold or diamond," said Dr. Dinesh Kumar Aswal, Director NPL.

Right now, Kibble balance has been developed by NPL to prepare weighs of one gram and it will be scaled up to prepare weighs of one kilogram in next three years or so, said Dr. Aswal.  Henceforth, all the SI units will be based on seven fundamental physical constants - Plank constant, speed of light in vacuum, hyperfine transition frequency, elementary charge, Boltzmann constant, Avogadro constant and luminous efficacy.

A recommendation to NCER has also been prepared to change the definitions in text books. A similar recommendation was released on Monday to make required changes in syllabus of metrology taught to engineering students.
"Weight will no more be measured on physical parameters. There will be transition pain. We are involved in many international projects, and when you supply equipment you have to be accurate in measurement", said Dr. Chidambaram.
The decision to redefine the four SI units was taken in November 2018 when metrologists and policy-makers from 60 countries around the world met at the General Conference on Weights and Measures in Versailles, France. (UNI)