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- India has adopted a global resolution to redefine four of the seven base units – kilogram, kelvin, mole and ampere. The changes have come into effect from May 20, 2019- World Metrology Day
- There are seven main units of measurement- a) metre for length, b) the kilogram for mass, c) the second for time, d) the ampere for electric current, e) the kelvin for temperature, f) the mole for the amount of a substance, and g) the candela for luminous intensity.
- Representatives from 60 countries had voted to redefine SI, or the International System of Units at the General Conference on Weights and Measures in Versailles, France in November 2018. The conference was organised by International Bureau of Weights and Measures (BIPM). BIPM sets the global standards for measurement. India is a member of BPIM since 1957.
- The kilogram’s definition will now be based on a concept of physics called the Planck constant. The Planck constant relates a photon’s energy to its frequency. It describes the behaviour of particles and waves on the atomic scale. It depends on three units: metre, kilogram and second.
- As second and metre are measured and defined using the speed of light, they can be used with the fixed Planck constant to define a kilogram. Using a machine called a Kibble balance, the value of the Planck constant has been fixed. It has been measured at 6.626069… × 10^ (-34) kilograms per second per square metre.
- The second is defined as the time it takes for a certain amount of energy to be released as radiation from atoms of Caesium-133. A metre is the distance travelled by light in vacuum in 1/299,792,458 of a second
- Until now the kilogram has been defined as the mass of a cylinder of platinum-iridium, called Le Grand K, or International Prototype Kilogram (IPK) which is kept at BIPM in Sèvres, near Paris. In India, National Physical Laboratory (NPL), custodian of the fundamental units of measurement, maintains the National Prototype Kilogram (NPK-57), which is calibrated with IPK.
- The IPK was the last physical artefact used to define any of the fundamental units. All measures are all now defined on the basis of unchanging universal, physics constants- the natural constants.
- According to experts, the change in definition of kilogram will ensure its reliability, and enable far more accurate mass measurements. Further, the new SI System will be helpful in bringing in accuracy while dealing with international trade, biotechnology, high-tech manufacturing and human health and safety.
- The NPL has released a set of recommendations requiring that school textbooks, engineering-education books, and course curriculum update the definition of the kilogram.
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