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কিছু স্থানে প্লাংক কন্সটেন্ট(h) এর স্থলে h bar (ħ) দেখিয়েছি।
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Attribution:
veritasium
VICE News
This video about roundest object in the world in bangla, mass unit kilogram prototype,how is planck's constant related to mass.
Video chapter:
00:00 - intro about roundest object
00:25 - history of mass unit kilogram
01:50 - mass unit kilogram prototype
03:25 - problem with mass unit kg prototype
04:31 - roundest object making
05:04 - roundest object use
06:17 - how is planck's constant related to mass
The kilogram was originally defined in 1795 as the mass of one litre of water. This definition was simple yet difficult to use in practice, due to the fact that the properties of the water are not defined. Modern superseding definitions of a kilogram are accurate to within 30 ppm of the mass of one litre of water. In 1799, the platinum Kilogramme des Archives replaced it as the standard of mass. In 1889, a cylinder of platinum-iridium, the International Prototype of the Kilogram (IPK) became the standard of the unit of mass for the metric system, and remained so until 2019.The kilogram was the last of the SI units to be defined by a physical artefact.
The kilogram is now defined in terms of the second and the metre, based on fixed fundamental constants of nature.This allows a properly-equipped metrology laboratory to calibrate a mass measurement instrument such as a Kibble balance as the primary standard to determine an exact kilogram mass, although the IPK and other precision kilogram masses remain in use as secondary standards for all ordinary purposes.
The world's roundest object helps solve the longest running problem in measurement -how to define the kilogram.A kilogram isn't what it used to be. Literally. The original name for it was the 'grave', proposed in 1793 but it fell victim to the French Revolution like its creator, Lavoisier. So begins the tale of the most unusual SI unit. The kilogram is the only base unit with a prefix in its name, and the only one still defined by a physical artifact, the international prototype kg or IPK.
But the problem with this definition has long been apparent. The IPK does not seem to maintain its mass compared to 40 similar cylinders minted at the same time. The goal is therefore to eliminate the kilogram's dependence on a physical object. Two main approaches are being considered to achieve this end: the Avogadro Project and the Watt Balance.
The Avogadro project aims to redefine Avogadro's constant (currently defined by the kilogram -- the number of atoms in 12 g of carbon-12) and reverse the relationship so that the kilogram is precisely specified by Avogadro's constant. This method required creating the most perfect sphere on Earth. It is made out of a single crystal of silicon 28 atoms. By carefully measuring the diameter, the volume can be precisely specified. Since the atom spacing of silicon is well known, the number of atoms in a sphere can be accurately calculated. This allows for a very precise determination of Avogadro's constant.
#BigganPiC #roundest_object #kilogram #kibble_balance #physics #science #planck_constant
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Read More:
wonderfulengineering.com/this...
en.wikipedia.org/wiki/Planck_...
en.wikipedia.org/wiki/Kilogram