+ The New Kilogramme - CII Blog

Four of the seven base units – kilogramme, kelvin, mole and ampere – have been redefined. The new definitions were aptly implemented across the world this year on May 20, which is World Meteorology Day. This move is expected to have far-reaching consequences, including changes in academic books all over the globe. 

This resolution to re-define these base units was passed by representatives of 60 countries at the General Conference on Weights and Measures (CGPM) of the International Bureau of Weights and Measures (BIPM), Paris, on 16th November 2018.

For years, over 100 countries have been following the International System of Units (SI), better known as the metric system, to have international coherence in measurements.  Since 1989, a kilogramme has been defined by the weight of a shiny piece of platinum-iridium metal called Le Grand K, held in Paris. Despite being locked in a jar, the mass of this piece of metal has been deteriorating over the years. In the last few decades, it had lost around 50 micrograms! One might think that such a small change would have no consequences, but a change is a change and is bound to have some effect. 

A need was, therefore, felt for a natural physical constant definition to the measure ‘kilogramme’.  This need was strengthened due to the advancements in science and technology which necessitated more accuracy in measurements. 

The Le Grand K was, therefore, abandoned and a new measuring instrument called the Kibble Balance was adopted to redefine a kilogramme. 

Kibble Balance

The Kibble Balance can be likened to a fruit-vendor’s weighing scale. By balancing the weights on either side, it determines the weight using gravitational forces. In the Kibble Balance, one of the scales is replaced by a coil in a magnetic field. The difference in masses is balanced with electromagnetic force instead of gravity. This method helps determine the value of the Planck Constant, named after Max Planck, a German physicist, and denoted by the symbol h. By measuring the current running through the electromagnet, h can be calculated to an accuracy of 0.000001%.

The Planck Constant is used to re-define the kilogramme.

The change in the definition of the kilogramme has given way to change in other measures such as ampere, kelvin and mole.

The Impact

Recommendations have been sent to educational institutions such as the All India Council for Technical Education (AICTE) to incorporate the change in their syllabus in engineering and other academic courses. The National Council of Educational Research and Training (NCERT) will also implement these changes in its curriculum.

The holistic purpose of a systems unit is to enable a global and coherent measurement system, and this is what the new system shall achieve. While it has paved the way for a brighter future with reduced space for error, it will also bring more accuracy while dealing with international trade, biotechnology and high-tech manufacturing, to name a few. 

This extra accuracy will prove to be a boon to scientists. Though the common man will not be able to see or feel this change in his/her day-to-day life, these re-definitions are expected to establish firm foundations of improved measurements for decades to come. 

The new Kilogramme is here to stay.