according to International System of Units (SI), the units of the seven basic quantities are: Current—— ampere （Ampere） Corresponding code: m, kg，s，K，A，cd，mol
The basic units of the International System of Units (SI) are defined as:
The meter (m) is the unit of length, and 1m is defined as "the distance that light travels in 1/299792458s in vacuum".
The kilogram (kg) is the unit of mass, and 1kg is defined as“ Planck constant It is the mass unit of 6.62607015 × 10 ⁻ ³ ≮ J · s ". The second (s) is the time unit, and 1s is defined as "cesium-133" Atomic ground state The transition between the two hyperfine energy levels of 9192631770 corresponds to the duration of the radiation ". Ampere (A) is the current unit, and 1A is defined as "within 1s (1/1.602176634) × 10 ^ 19 Charge shift Generated current intensity ".
Kelvin (K) is Thermodynamic temperature Unit, 1K is defined as "corresponding Boltzmann constant Is 1.380649 × 10 ^ - 23J · K ^ - 1. Mole (mol) is the unit of measurement of substances, and 1mol is defined as "the amount of substances in a system that accurately contains 6.02214076 × 10 ² ³ atoms or molecules and other basic units".
Candela (cd) is the unit of luminous intensity, and 1cd is defined as "the luminous intensity of a light source in a given direction light source It emits monochromatic radiation with a frequency of 540 × 10 ¹² Hz, and the radiation intensity in this direction is 1/683 watt / Sphericity“ 。 In the International System of Units, the unit of plane angle - radian and solid angle - sphericity is not included in the basic unit or derived unit, but is called auxiliary unit. Auxiliary units can be used as both basic units and Export Units use. They are defined as follows: radian (rad) is the size of the plane angle between two radii in a circle when the arc length intercepted on the circumference is equal to the radius. Sphericity (sr) is a solid angle whose vertex be located The center of the sphere, and the area it intercepts on the sphere is equal to the area of the square with the radius of the sphere as the side length. After the basic unit and auxiliary unit are selected, according to the relationship between physical quantities, the unit formed by multiplication or division of basic unit and auxiliary unit is called derived unit.
Basic unit of unit system
Name of quantity | Unit name | Unit symbol |
length | rice | m |
quality | Kg | kg |
time | second | s |
electric current | Safety | A |
Thermodynamic temperature | Kelvin | K |
Amount of substance | Mohr | mol |
Luminous intensity | Kandra | cd |
Exported units including auxiliary units with special names in the unit system
Name of quantity | Unit name | Unit symbol | Examples of other expressions |
Plane angle | radian | rad | m/m=1 |
Solid angle | Sphericity | sr | m/m=1 |
frequency | Hertz | Hz | s |
Force | Cattle | N | kg.m/s |
Pressure | Pascal | Pa | N/m |
Energy | Joule | J | N.m |
Power | Watts | W | J/s |
Charge quantity | Coulomb | C | A.s |
Potential | Volts | V | W/A |
capacitance | Farad | F | C/V |
resistance | Oum | Ω | V/A |
conductance | West (door) | S | A/V |
Magnetic flux | Weber | Wb | V.s |
Magnetic flux density | Te (Sra) | T | Wb/m |
inductance | Heng (Li) | H | Wb/A |
Celsius temperature | centigrade | ℃ | - |
Luminous flux | Flow | lm | Cd·sr |
Illuminance | Le (x) | lx | lm/m |
Activity | Becquerel | Bq | s |
absorbed dose | Ge (Rui) | Gy | J/Kg |
Dose equivalent | Heath | Sv | J/Kg |
Non SI units selected by the state
Name of quantity | Unit name | Unit symbol | Conversion relationship and description |
time | branch Hour Days | min h d | 1min=60s 1h=60min=3600s 1d=24h=86400s |
Plane angle | (angle) second (jiao) min degree | （〞） （ˊ） （°） | 1〞=（ ∏/648000）rad（ π is pi) 1ˊ=60〞=（ ∏/10800）rad 1°=60ˊ=（ ∏/180）rad |
Rotation speed | Rpm | r/min | 1r/min=（1/60）s |
length | in the sea | n mile | 1n mile=1852m (Applicable to navigation only) |
speed | section | kn | 1 kn=1n mile/h= （1852/3600m/s (Applicable to navigation only) |
quality | ton Atomic mass unit | t u | 1t=1000kg 1u≈1.6605655×10kg |
can | Electron volt | eV | 1eV≈1.602177×10J |
volume | rise | L, (1) | 1L=1dm=10m |
Gradational difference | Decibel | dB | - |
Linear density | Tex | tex | 1tex=1g/km |
Land area | hectare | hm two | 1hm two =10000m two =0.01km two |
Prefixes used to form decimal multiples
Factor represented | Preface name | Prefixes |
10 to the 24th power | Yao | Y |
21 times of 10 square | Ze | Z |
18 times of 10 square | Ai (Kesa) | E |
15 times of 10 square | Pat | P |
12 times of 10 square | Too | T |
9 of 10 square | Ji (coffee) | G |
6 times of 10 square | Mega | M |
3 times of 10 square | thousand | k |
Twice of 10 square | hundred | h |
Once in 10 square | ten | e |
10 minus 1 time square | branch | d |
10 minus twice square | Per cent | c |
10 minus 3 times square | Millionth | m |
10 minus 6 times square | tiny | μ |
10 minus 9 times square | Na | n |
10 minus 12 times square | Pi (Ke) | p |
10 minus 15 times square | Fly (female bracket) | f |
10 minus 18 times square | Ato | a |
10 minus 21 times square | Chek (Putuo) | z |
10 minus 24 times square | Unidae | y |
