Current Definition
On 20 May 2019, he new and
current definition of the kilogram went into
effect[9]. It is as follows: "The
kilogram, symbol kg, is the SI unit of mass. It
is defined by taking the fixed numerical value
of the Planck constant h
to be 6.62607015×10−34 when expressed
in the unit J⋅s, which is equal to kg⋅m2⋅s−1."
With the kilogram no longer tied to a physical
object, it can be reproduced using any method
involving the Planck constant, including the
Kibble balance method and the Avogadro method.
Scientists can even obtain a kilogram by
measuring the energy of photons using the
Planck-Einstein relation E=hν and
Einstein's mass-energy equivalence E=mc2.
This flexibility is important because
scientists can calibrate their instruments
on-site with certainty, where previously they
relied on calibration from a copy of a copy of
a platinum-iridium cylinder, which was prone
to deviation, however slight.
Index
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