World Metrology Day: Kilogram will have new definition from today!


Every year May 20 is observed as World Merology Day for celebrating the International System of Units. Metrology is the study of measurements. On this day, the Meter Convention(the Treaty of Meter) was signed in 1875 in Paris by representatives of 17 nations (Argentina, Austria-Hungary, Belgium, Brazil, Denmark, France, Germany, Italy, Peru, Portugal, Russia, Spain, Sweden and Norway, Switzerland, Ottoman Empire, United States of America, and Venezuela). 

The Metrology day 2019 will mark the changes in the International system that were decided in 2018. Last year in November 2018, at the General Conference on Weights and Measures in Versailles, scientists voted for the change. Under this, the kilogram will get redefined based on the Planck's constant i.e. the ratio of energy to frequency of a photon, measured to its most precise value.

Till now, the definition of kilogram was simple and was defined by the mass of a hunk of platinum-iridium alloy(90 percent platinum and 10 percent iridium) that has been kept at the International Bureau of Weights and Measures in Sèvres, France since 1889. It is known as the International Prototype Kilogram(Big K). As Big K is man-made, it is not accurate. If the Big K changes its weight, everything needs to be adjusted. It not constant and has loosed 50 micrograms of weight from the time it is created. Hence, to have more accurate deginition for kilogram, the change in the definition was proposed.

The new difinition will be based on the Planck constant, the speed of light and the resonant frequency of the caesium atom. The units of the Planck constant are kgm2s-1, so need to first have the metre defined(in terms of the speed of light) and the second (in terms of the caesium atom in the atomic clock). 

This change would not make any difference to the common people as a kilogram of mangoes before the change will still going to be a kilogram of mangoes after the change. It will make difference to the scientists and metrologists.

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