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SI derived unit
From Wikipedia, the free encyclopedia
SI derived units are part of the SI system of measurement units and are derived from the seven SI base units.
Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter (eg: meter, m; hertz, Hz). The exception is degrees Celsius, which refers to degrees on the Celsius scale.
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[edit] Derived units with special names
Base units can be put together to derive units of measurement for other quantities. In addition to the two dimensionless derived units radian (rad) and steradian (sr) there are 20 derived units having special names:
| Name | Symbol | Quantity | Expression in terms of other units | Expression in terms of SI base units |
|---|---|---|---|---|
| hertz | Hz | frequency | 1/s | s-1 |
| radian | rad | angle | m∙m-1 | dimensionless |
| steradian | sr | solid angle | m2∙m-2 | dimensionless |
| newton | N | force, weight | m∙kg/s2 | m∙kg∙s−2 |
| pascal | Pa | pressure, stress | N/m2 | m−1∙kg∙s−2 |
| joule | J | energy, work, heat | N∙m = C·V = W·s | m2∙kg∙s−2 |
| watt | W | power, radiant flux | J/s = V·A | m2∙kg∙s−3 |
| coulomb | C | electric charge or electric flux | s∙A | s∙A |
| volt | V | voltage, electrical potential difference, electromotive force | W/A = J/C | m2∙kg∙s−3∙A−1 |
| farad | F | electric capacitance | C/V | m−2∙kg−1∙s4∙A2 |
| ohm | Ω | electric resistance, impedance, reactance | V/A | m2∙kg∙s−3∙A−2 |
| siemens | S | electrical conductance | 1/Ω | m−2∙kg−1∙s3∙A2 |
| weber | Wb | magnetic flux | J/A | m2∙kg∙s−2∙A−1 |
| tesla | T | magnetic field | V∙s/m2 = Wb/m2 = N/(A∙m) | kg∙s−2∙A−1 |
| henry | H | inductance | V∙s/A = Wb/A | m2∙kg∙s−2∙A−2 |
| degree Celsius | °C | temperature | K − 273.15 | K − 273.15 |
| lumen | lm | luminous flux | lx·m2 | cd·sr |
| lux | lx | illuminance | lm/m2 | m−2∙cd∙sr |
| becquerel | Bq | radioactivity (decays per unit time) | 1/s | s−1 |
| gray | Gy | absorbed dose (of ionizing radiation) | J/kg | m2∙s−2 |
| sievert | Sv | equivalent dose (of ionizing radiation) | J/kg | m2∙s−2 |
| katal | kat | catalytic activity | mol/s | s−1∙mol |
Note that other units such as the litre are not SI units, but are accepted for use with SI. See non-SI units accepted for use with SI.
[edit] Other quantities and units
| Compound units derived from SI units | ||||
|---|---|---|---|---|
| Name | Symbol | Quantity | Expression in terms of SI base units |
|
| square metre | m2 | area | m2 | |
| cubic metre | m3 | volume | m3 | |
| metre per second | m/s | speed, velocity | m·s−1 | |
| cubic metre per second | m3/s | volumetric flow | m3·s−1 | |
| metre per second squared | m/s2 | acceleration | m·s−2 | |
| metre per second cubed | m/s3 | jerk, jolt | m·s−3 | |
| metre per quartic second | m/s4 | snap | m·s−4 | |
| radian per second | rad/s | angular velocity | s−1 | |
| newton second | N·s | momentum, impulse | kg·m·s−1 | |
| newton metre second | N·m·s | angular momentum | kg·m2·s−1 | |
| newton metre | N·m | torque, moment of force | kg·m2·s−2 | |
| reciprocal metre | m−1 | wavenumber | m−1 | |
| kilogram per cubic metre | kg/m3 | density, mass density | kg·m−3 | |
| cubic metre per kilogram | m3/kg | specific volume | kg−1·m3 | |
| mole per cubic metre | mol/m3 | amount (-of-substance) concentration | m−3·mol | |
| cubic metre per mole | m3/mol | molar volume | m3·mol−1 | |
| joule per kelvin | J/K | heat capacity, entropy | kg·m2·s−2·K−1 | |
| joule per kelvin mole | J/(K·mol) | molar heat capacity, molar entropy | kg·m2·s−2·K−1·mol−1 | |
| joule per kilogram kelvin | J/(K·kg) | specific heat capacity, specific entropy | m2·s−2·K−1 | |
| joule per mole | J/mol | molar energy | kg·m2·s−2·mol−1 | |
| joule per kilogram | J/kg | specific energy | m2·s−2 | |
| joule per cubic metre | J/m3 | energy density | kg·m−1·s−2 | |
| newton per metre | N/m = J/m2 | surface tension | kg·s−2 | |
| watt per square metre | W/m2 | heat flux density, irradiance | kg·s−3 | |
| watt per metre kelvin | W/(m·K) | thermal conductivity | kg·m·s−3·K−1 | |
| square metre per second | m2/s | kinematic viscosity, diffusion coefficient | m2·s−1 | |
| pascal second | Pa·s = N·s/m2 | dynamic viscosity | kg·m−1·s−1 | |
| coulomb per cubic metre | C/m3 | electric charge density | m−3·s·A | |
| ampere per square metre | A/m2 | electric current density | A·m−2 | |
| siemens per metre | S/m | conductivity | kg−1·m−3·s3·A2 | |
| siemens square metre per mole | S·m2/mol | molar conductivity | kg-1·s3·mol−1·A2 | |
| farad per metre | F/m | permittivity | kg−1·m−3·s4·A2 | |
| henry per metre | H/m | permeability | kg·m·s−2·A−2 | |
| volt per metre | V/m | electric field strength | kg·m·s−3·A−1 | |
| ampere per metre | A/m | magnetic field strength | A·m−1 | |
| candela per square metre | cd/m2 | luminance | cd·m−2 | |
| coulomb per kilogram | C/kg | exposure (X and gamma rays) | kg−1·s·A | |
| gray per second | Gy/s | absorbed dose rate | m2·s−3 | |
| ohm metre | Ω·m | resistivity | kg·m3·s−3·A−2 | |
| kilometres per hour | km/h | speed, velocity | km·h-1 | |
[edit] See also
[edit] References
- I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC: Quantities, Units and Symbols in Physical Chemistry, 2nd edition (June 1993), Blackwell Science Inc (p. 72)
