World’s standard definition of kilogram now redefined
17, Nov 2018
Prelims level : Kilogram and Weighing system, Planck’s constant Mains level : Need for redefining, about the new system, significance and the process of redefining.
Why in news?
- The 26th meeting of the General Conference on Weights and Measures (CGPM) was held during November at Palais des Congréss, Versailles, France.
- In the meeting, the members have voted for the redefinition of 130 years old “Le grand K – the SI unit of kg” in terms of the fundamental Planck’s constant (h).
- The new definitions will come into force on 20 May 2019.
Why to redefine standards?
- In a world where accurate measurement is now critical in many areas, such as in drug development, nanotechnology and precision engineering – those responsible for maintaining the international system had no option but to move beyond Le Grand K to a more robust definition.
- The International Bureau of Weights and Measures (BIPM), the main executive body of CGPM has the responsibility of defining the International System of Units (SI).
- This revision of the SI is the culmination of many years of intensive scientific cooperation between the National Metrology Institutes (The national Physical Laboratory for India) and the BIPM.
- The dissemination of SI units for the welfare of society and industries in the country is the responsibility of Legal Metrology, Department of Consumer Affairs, GoI.
How effective is the new system?
- Electromagnets generate a force. Scrap-yards use them on cranes to lift and move large metal objects, such as old cars. The pull of the electromagnet, the force it exerts, is directly related to the amount of electrical current going through its coils. There is, therefore, a direct relationship between electricity and weight.
- So, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to counteract the weight (gravitational force acting on a mass).
- The fluctuation is about 50 parts in a billion, less than the weight of a single eyelash. But although it is tiny, the change can have important consequences.
- There is a quantity that relates weight to electrical current, called Planck’s constant – named after the German physicist Max Planck and denoted by the symbol h.
- But h is an incredibly small number and to measure it, the research scientist Dr Bryan Kibble built a super-accurate set of scales. The Kibble balance, as it has become known, has an electromagnet that pulls down on one side of the scales and a weight – say, a kilogram – on the other. The electrical current going through the electromagnet is increased until the two sides are perfectly balanced.
- By measuring the current running through the electromagnet to incredible precision, the researchers are able to calculate h to an accuracy of 0.000001%. This breakthrough has paved the way for Le Grand K to be deposed by “die kleine h”.
New Universal System of standard:
- After the kilogram’s definition is changed officially- on 20th May, 2019, also known as World Metrology Day- most people will never notice the difference.
- It would not change baking ingredients on a kitchen scale, or even have an effect on the tons of goods shipped globally every day.
- For astronomers calculating the movements of stars and galaxies or for pharmacologists trying to define doses of medications sown to the molecule, the new standard of measurement could change the way they work.
- The metric system was intended to be rational, universal set of units “for all people, for all time”.
- The SI unit will finally be truly universal system, free of any human artifacts.