The International System of Units is a globally recognized measurement system consisting of seven basic units, namely the length unit “m”, the mass unit “kilogram”, the time unit “second”, the current intensity unit “ampere”, and the thermodynamic temperature unit “Kelvin”. The unit of quantity of matter "molar" and the unit of luminous intensity "candela".
On the 16th, the 26th International Metrology Conference passed the resolution of “Amendment of the International System of Units” and officially updated the definition of four basic units including the international standard quality unit “kg”. The new international unit system will come into effect on May 20, 2019, the World Measurement Day.
This new international unit system uses physical constants to redefine the mass unit "kilogram", the current unit "ampere", the temperature unit "Kelvin" and the quantity unit "molar" of the substance. Defining the unit of measurement with basic physical constants can greatly improve stability and accuracy. Among them, the most concerned definition of "kilogram" will be based on the Planck constant in quantum mechanics.
For nearly 130 years, the mass unit of "1 kg" has been defined by a platinum-rhodium alloy cylinder of diameter and height of about 39 mm, which is the "international kilogram original", and the nickname is "large K".
"Big K" has been placed in the underground of Paris, and its box is vacuum-sealed by a 3-layer large clock-shaped glass, which has a strong confidentiality.
Up to now, "Big K" has come out four times in total, and has breathed the air four times. Although the scientists have taken extra care to protect it when they took it out, it was fattened by the air because it was polluted by the air. And at the same time, because oxidation has become thinner. Although the error is not very large, the calculation of the error with micrograms is still relatively large, and the error reaches 1-2 particle dust weight.
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Therefore, on May 20, 2019, people will begin to calculate the Planck constant of photon energy in quantum mechanics as the new standard, and will use the most accurate Watt Balance to redefine the "kilogram". .
The principle is to convert the mechanical force required to move a mass of 1 kilogram into an electromagnetic force expressed by the Planck constant, and then calculate the mass by the mass energy conversion formula.
The advantage of the quantum measurement benchmark is very obvious. Firstly, the accuracy of the quantum measurement benchmark is relatively high, generally up to several orders of magnitude higher than the physical measurement benchmark. Secondly, the quantum measurement benchmark is a physical experimental device, so the same principle can be followed. Recurring in different places, which avoids many problems caused by multiple passes of magnitude.
So for the redefined "kilograms (kg)", will the weighing method for redefining the weight change?
Although kilograms (kg) has been redefined, it is still based on the current kilogram (kg) value, and the two can be seamlessly connected. The mass unit values under the two definitions ensure continuity. Therefore, the doubts about everyone will not happen, and the redefinition of the measurement will not affect the daily life.
This redefined kilogram only emits heat in scientific research. Its role is mostly used in scientific research, such as calculations, pharmaceutical calculations, climate changes, etc. For the research and development of some precision instruments, the unit of measurement Accuracy to micrograms is necessary.
It should be noted that a few decades ago, metrologists redefine meters and seconds with the speed of light and the cesium atomic clock. With the increasing accuracy of scientists' measurement of natural constants in recent years, the definitions of other units have been updated, and more perfect and long-lasting measurement standards will eventually become possible.
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