SI derived unit: Difference between revisions
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* 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) |
* 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) |
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[[Category:SI units|Derived unit]] |
[[Category:SI units|Derived unit]] |
Revision as of 16:52, 27 May 2010
The International System of Units (SI) specifies a set of seven base units from which all other units of measurement are formed. These other units are called SI derived units and are also considered part of the standard.
The names of SI units are always written in lowercase. The unit symbols of units named after persons, however, are always spelled with an initial capital letter (e.g., the symbol of hertz is Hz; but metre becomes m). The exception is the Celsius, which refers to divisions on the Celsius temperature scale.
Derived units with special names
Base units can be combined to derive units of measurement for other quantities. In addition to the two dimensionless derived units radian (rad) and steradian (sr), 20 other derived units have 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 | kg∙m/s2 | kg∙m∙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 strength, magnetic flux density | 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 |
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 |
Other common units, such as the litre, are not SI units, but are accepted for use with SI (cf. non-SI units accepted for use with SI).
Other quantities and units
See also
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)