Electronics, Instrumentation, Magnetism, Materials, Mechanics, News

New definition of kilogram

Has been appeared a new system to kilogram definition. But it will only take effect on 20 May 2019.

Source: Big think

Since 1889, the definition of a kilogram has been the mass of one particular chunk of platinum-iridium alloy called the International Prototype Kilogram, stored at the International Bureau of Weights and Measures in Sèvres, France.

This is the chunk of platinum-iridium generated by a computer, it is a cylinder with 90% platinum and 10% iridium. Lost 50 micrograms in 100 years due to loss of atoms and air absorption.

This cylindrical hunk of metal, nicknamed Big K, has many copies around the world that are used to calibrate scales and keep society in agreement on what constitutes a kilogram and other units of measurement.

On Friday morning, scientists at the General Conference on Weights and Measures in Versailles voted to change the definition of a kilogram, opting to affix it to a physical constant that will never change, whether you’re measuring it on Earth or light years away in the cosmos.

The kilogram will be related to Planck constant (h=6,63\cdot 10^{-34}J\cdot s). This is one of the fundamental constants of quantum physics.

Now, you just need a Kibble balance, which, in simplified terms, can find Planck’s constant by translating the mechanical energy produced by the mass of an object into an equivalent amount of electrical energy. The Kibble balance is a highly expensive and complicated instrument, but they could become cheaper and more accessible in the future.

This is the schematics of a Kibble balance.

On one side, there is an adjustable current source. This current supplies an electromagnet, inside a magnetic field, which creates a force upward. This force is in opposite direction to the weight of mass test. A calibration system with laser measures the speed and coil position, when the mass M is removed. The laser system’s sensor sends the signal to the current source.

In daily lives won’t change anything. But it is important to researches.

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About Pedro Ney Stroski

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