国际单位制（International system of units）
In October 1960, the eleven International Conference on Metrology defined the international system of international units, referred to as the SI system.
SI system: seven basic units: length m, time s, mass kg, thermodynamic temperature (Kelvin temperature) K, current unit A, light intensity unit CD (Candela), mass mol
Two auxiliary units: flat angle radian rad, solid corner corner degree Sr
The definition of the basic unit of SI
M: length of path passed in a vacuum (1/299, 792458) s time interval. [Seventeenth International Conference on Metrology (1983)]
Kilogram: the quality of an international kilogram of raw materials. [First International Conference on Metrology (1889) and Third International Conference on Metrology (1901)]
The duration of the 9192631770 cycles corresponding to the transition between the two hyperfine levels of the atomic -133 ground state. [Thirteenth International Congress on Metrology (1967), resolution 1]
A: in a vacuum, infinite two sectional area of negligible distance 1 m parallel circle straight wire pass with equal constant current, if the interaction between wires in each meter length is 2 * 10-7 N, the current in each wire is 1 A.
[International Commission on measurement (1946) resolution 2. Approval of the Ninth International Conference on Metrology (1948)
Kelvin: the thermodynamic temperature of the three-phase point of water is 1/273.16. [Thirteenth International Congress on Metrology (1967), resolution 4]
Moore: is a system of amount of substance, the basic unit contained in the system (a specific combination of atoms, molecules, ions, electrons and other particles, and these particles) and 0.012 kg carbon atom number equal to -12. [Fourteenth International Congress on Metrology (1971), resolution 3]
Candela: the luminous intensity of a light source in a given direction. The light source emits monochromatic radiation with a frequency of 540 * 1012 Hz, and the radiation intensity in this direction is (1/683) W/sr. [Sixteenth International Congress on Metrology (1979), resolution 3]
Basic quantity and derived quantity
Physical quantities are related by describing the laws of nature or by defining equations for new physical quantities. Therefore, a few physical quantities can be independent of each other, and other physical quantities can be defined or represented by equations. These few are regarded as independent quantities of physical quantities, called basic physical quantities, referred to as basic quantities. The rest of the physical quantities that can be derived from elementary
quantities are called derived physical quantities, referred to as export quantities. In the international system of units, there are seven basic quantities: length, quality, time, current, thermodynamic temperature, material quantity and luminous intensity. All other quantities in physics can be derived from the seven fundamental quantities by multiplication, division, differentiation, or integration.
1. SI basic units
Quantity name, unit name, code definition
Dimension code
The length of m m M. equal to the radiation corresponding to the transition between the 2p10 and 5d5 levels of krypton -86 atoms, the length of the 1650763.67 wavelengths in the vacuum. L
The mass is kilogram Kg 1 kg, equal to the quality of the international kilogram precursor.
M
The duration of the 9192631770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the cesium -133 atom ground state is s. T
Ampere ampere A ampere is a constant current. If it is kept in a parallel straight wire with a length of one meter apart in a vacuum, the length of each meter is equal to 2X10-7 newton.
Thermodynamics, temperature, Kelvin, K, thermodynamics, temperature, unit Kelvin, water, triple point, thermodynamic temperature, 1/273.16. .
The amount of material mol mol is a systematic quantity of matter, and the basic unit contained in the system is equal to the number of atoms of 0.012 kilograms of carbon -12. N
The luminescence intensity of CD Kandela for frequency of 540X1012 Hz monochromatic radiation, the radiation intensity in a given direction for each surface of 1/683 W. J
2.SI export unit
Quantity SI units
kilogramOther representations are represented in SI basic units
Frequency Hz (s-1) Hz
Force cattle (Dayton), N, m.kg.s-2
Pressure (stress), Palmer (Oscar), Pa, N/m2, m-1.kg.s-2
Energy, work, heat, coke (ear), J, Nm, m2.kg.s-2
Power, radial (flux) watts (especially), W, J/s, m2.kg.s-3
Power, charge Library (Lun), C, s.A
Voltage, potential, electromotive force, volts (especially), V, W/A, m2.kg.s-3.A-1
Capacitor (pull) F C/V m-2.kg-1.s4.A2
Ohm ohm (omega) V/A m2.kg.s-3.A-2
West (Siemens) S A/V conductivity m-2.kg-1.s3.A2
Magnetic flux (Wei) Wb (m2.kg.s-2.A-1) V.s
Magnetic flux density, magnetic flux density (LA), T, Wb/m2, kg.s-2.A-1
Inductance Heng (LI) H Wb/A m2.kg.s-2.A-2
The Celsius temperature is C degrees centigrade. K
Flux (Ming) LM cd.sr
(illumination) illumination Le (Kors) LX lm/m2 m-2.cd.sr
(radioactive) BQ (Bq S-1 lrrr) activity
Absorbed dose Ge (Rui) Gy, J/kg, m2.s-2
Dose equivalent * (Voight) Sv J/kg m2.s-2
3.SI prefix

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