Between physical quantitiesLaws of physicsAnd related definitions.People often take some of them asBasic physical quantity, take their units as the basic units, form a supporting unit system, and other units can be derived from it, which isUnit system。
Due to historical reasons, countries all over the world have adopted variousUnit system, chaos and complexity.The units used in different industries are also different. For example, France used to use the meter ton second system, and Britain and the United States used to use the foot pound second system. The engineering unit system, namely the meter kilogram force second system, was used in the technical field, while physics was accustomed to the centimeter gram second (CGS) unit system.This is very detrimental to economic exchanges and scientific and technological work.In order to facilitate international exchange of industrial technology, it was signed in 1875Metric ConventionIs specified in metersLength unit, withKgIs the quality unit, and the second is the time unit.This is known as the meter kilogram second (MKS) system of units.
rice: The length of the path of light in vacuum within 1/299792458s time interval.
In 1960International Conference on MetrologyAt the same time of determining the above definition, it announced the abolition of the definition of meters based on the platinum iridium international rice prototype, which came into effect in 1889.
In 1792,French National AssemblyThe decision to establish a new unit of length should be related to the arc length of the earth's ellipsoid meridian.For this reason, the radian was measured from 1792 to 1797, and the Drambol ellipsoid in 1800 was calculated. The length unit is one forty million times the length of its meridian circle, which is called 1 meter.At the World Length Conference held in Paris in 1872, it was decided to manufacture 31 "meter prototype rulers", each of which was numbered.Except N0.6, which is the international original ruler, all others are based on the international prototype ruler. They are precisely calibrated, and the length is calculated. They are distributed to countries for preservation as the standard of length units.Since China has not joined the International Association of Weights and Measures, it has not obtained the meter prototype ruler.This kind of material object "meter" is defined as "1 meter is the distance between the two scribes of N0.6 'meter prototype scale' at the melting point temperature of ice." Its disadvantages are: difficult to reproduce, easy to damage;It changes slowly with time;The precision is not high enough, only 1~2 × 10 ^ - 6;A few countries have, which cannot meet the requirements of length transmission in most countries.Therefore, physical rice needs to be replaced by natural rice.
In 1960, the 11th International Metrology Conference adopted the definition of light wave meter, and the second "meter" was defined as "the transition radiation between 2P10 and 5d5 energy levels of krypton-86 atom in vacuum with a wavelength of 1650763.73 times is 1 meter." The profile of krypton-86 spectral line is slightly asymmetric, and the reproduction accuracy of light wave meter in the laboratory is 4 × 10-9.
In 1983, the 17th International Conference on Metrology adopted the third definition of the speed of light meter, "1 meter is the distance that light travels in a vacuum within 299792458 seconds."[1]
Kg
Symbol: kg
Kg: corresponding to the mass unit when Planck constant is 6.62607015 × 10 ^ - 34J · s.
The International Kilogram Prototype was approved to be manufactured by the First International Conference on Weights and Quotations in 1889Platinum iridium alloyMade cylinder.The prototype is kept at the International Bureau of Metrology, Paris.
On November 16, 2018, the International Conference on Metrology adopted a resolution that 1kg is defined as "the mass unit corresponding to the Planck constant of 6.62607015 × 10 ^ - 34J · s".
second
Symbol: s
second: The duration of 9192631770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of cesium-133 atom is 1 s.
At first, people divided a day and night into 24 hours, one hour is 60 minutes, and one minute is 60 seconds. But the cycle of a day and night, that is, the solar day, is variable, so 1 s is defined as the average solar day. Later, it was found that the cycle of the earth's revolution is also variable, so another definition needs to be determined.With the development of science and technology, scientists have found that when atomic energy levels transition, they absorb or emit electromagnetic waves of a certain frequency, and their frequency is very stable.Therefore, the above definition was confirmed at the 13th International Metrology Conference in 1967.
ampere
Symbol: A
ampere: the current corresponding to 1/1.602176634 × 10 ^ 19 electrons in unit time.
In 1948, the ninth meeting of the International Commission on Weights and Measures made such provisions.In October 1960, it was recognized as one of the seven basic units in the International System of Units at the 11th International Congress of Weights.
As it involves operations that cannot be accurately repeated in the laboratory, ampere has been defined by the amount of charge carried by the unit proton (basic charge).
On November 16, 2018, the International Conference on Metrology passed a resolution that ampere is defined as "the current corresponding to 1/1.602176634 × 10 ^ 19 electrons per unit time"
Original definition: the thermodynamic temperature of the triple point of water is 273.16 K.
The unit is named after the British physicist KelvinThe temperature interval of "Kelvin" is equal to that of "Celsius"butKelvin scaleIs 273.15 degrees below zero (- 273.15 ℃) on the Celsius scale.
In 1968, the International Conference on Metrology decided to take "Kelvin" as one of the seven basic units.
On November 16, 2018, the International Metrology Conference passed a resolution that 1 Kelvin was defined as "the thermodynamic temperature corresponding to the Boltzmann constant of 1.380649 × 10 ^ - 23J · K ^ - 1".
Based on the definition of Boltzmann constant, Kelvin relates the average kinetic energy of a gas molecule to its absolute temperature.This definition improves the measurement accuracy of extreme low temperature and extreme high temperature.
mole
Symbol: mol
mole: The amount of material in a system that accurately contains 6.02214076 × 10 ^ 23 atoms or molecules and other basic units.
Original definition: included in the systemBasic unitAnd 0.012kg carbon-12.
Mole is simply called "Mo." It is the amount of material in a system.When using the mole, the basic unit should be specified, which can be atoms, molecules, ions, electrons and other particles, or a specific combination of these particles.
The original meaning of Moore's Latin is large quantity and heap quantity.It is a unit for measuring microscopic particles with macroscopic quantities.In 1971, the 14th International Conference on Metrology adopted the definition of mole.In 1977, the State Council of China announced the document introducing Moore, and canceled it at the same timeGram atom, mole,Molarity concentration, molar volume, etc.
On November 16, 2018, the International Conference on Metrology adopted a resolution that 1 mole is defined as "the amount of material in a system that accurately contains 6.02214076 × 10 ^ 23 atoms or molecules and other basic units".At the same time, the Avogadro constant was modified to 6.02214076 × 10 ^ 23.
Candela
Symbols: cd
Candela: Referred to as ridge, the luminous intensity of a light source in a given direction.The frequency emitted by the light source is 540 × 10 ^ 12HzhertzAnd in this directionradiation intensityIs (1/683)watt/Sphericity。
In the early 20th century, the United States, France and Britain once defined Candela by the luminous intensity of carbon filament lamps.
In 1993, metrologists improved the definition accuracy based on blackbody radiation. In 1948, the definition was accepted and later replaced with the current definition.
