Jul 20, 2020

**What is the news?**

The SI, the modern metric system, has seven base units from which all other measurement units can be derived. On May 20, 2019, four of them — the kilogram, kelvin, ampere and mole — were redefined in terms of constants of nature. Initially artefacts or physical objects were used to define base units. This created inaccuracies particularly for small measurements as physical object decay with time.

The remaining three — the second, meter, and candela — are already based on universal constants.

The fundamental constants are invariants of time and space and have successfully replaced the artefact-based units, and aptly opened up the new era for quantum world by linking all seven base units to fundamental constants or quantum standards. Now measurements will be more accurate meeting need of modern advance science based on precision.

**What is old definition of Kg?**

The kilogram has been defined since 1889 by a shiny piece of platinum-iridium held in Paris. All modern mass measurements are traceable back to it - from micrograms of pharmaceutical medicines to kilos of apples and pears and tonnes of steel or cement. This is international prototype, whose copy every nation keeps, including India. These copies give measurement of kilo for countries.

**What are issues with it?**

The previous definition of kilogram was based on the mass of the international prototype ‘kilogram’ which is an artefact. Prototype in Paris and its copies worldwide decay with time, deteriorate creating errors in measurements. however, the new definition is based on physical constant of nature. Which is something more constant. So, a kilogram will be defined by a tiny but immutable fundamental value called the Planck constant.

**What is need of new definition?**

Since The 1960s, we have to rely ever more heavily on advanced science and engineering in our day-to-day lives, and also in manufacturing, healthcare and science. This era demands very high accuracy in fields like precious metals, diamonds, nano pharmaceuticals. The unit redefinitions represent a profound change of perspective and they are expected to form the foundations of improved measurements for decades to come as science and technology continues to develop in a way, we cannot currently foresee.

**What is new definition of kg?**

The new definition of kg involves accurate weighing machines called 'Kibble balance', which uses Planck's Constant to measure the mass of an object using a precisely measured electromagnetic force.

**What is significance of new definition of Kg?**

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 change in the definition of kilogram will not have any implication in daily life. But in weighing of pharma and precious metals, it will matter when it comes to measurements less than a kilogram. For instance, measuring smaller diamonds.

**What is The International System of Units (SI)?**

The purpose of system units is to enable worldwide coherence of measurements. The International System of Units (SI) was formalized in 1960 and has been updated several times to account for development in measurement technology.

**What are seven base units?**

The kilogram, kelvin, ampere, mole, the second, meter, and candela from which all other measurement units can be derived. Table of new definitions.

SI UNIT | The Fundamental constant with fixed numerical value that is used to define SI UNIT in new system |

Second – Unit of Time | cesium frequency ∆ν_{C} |

Meter – Unit of Length | speed of light in vacuum c |

Kilogram – Unit of Mass | Planck constant h |

Ampere – Unit of Electric Current | the elementary charge e |

Kelvin – Unit of Thermodynamic Temperature | Boltzmann constant k |

Mole – Unit of Amount of Substance | Avogadro constant, N_{A} |

Candela – Unit of Luminous Intensity | luminous efficacy of monochromatic radiation of frequency 540 × 10^{12} Hz |