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|Quantity of heat||joule||Q|
|Radiant power (flux)||watt||P|
|Sound energy flux||watt||W|
|Specific heat capacity||joule/(kilogram * Kelvin)||c|
|Speed of sound||meter/second||n|
|Thermal conductivity||watt/(meter * Kelvin)||l|
Table 1. SI base units
Table 2. Examples of SI derived units
|SI derived unit
|speed, velocity||meter per second||m/s|
|acceleration||meter per second squared||m/s2|
|wave number||reciprocal meter||m-1|
|mass density||kilogram per cubic meter||kg/m3|
|specific volume||cubic meter per kilogram||m3/kg|
|current density||ampere per square meter||A/m2|
|magnetic field strength||ampere per meter||A/m|
|amount-of-substance concentration||mole per cubic meter||mol/m3|
|luminance||candela per square meter||cd/m2|
|mass fraction||kilogram per kilogram, which may be represented by the number 1||kg/kg = 1|
|For ease of understanding and convenience, 22 SI derived units have been given special names and symbols,
as shown in Table 3.
For a graphical illustration of how the 22 derived units with special names and symbols given in Table 3 are related to the seven SI base units, see relationships among SI units.
Note on degree Celsius. The derived unit in Table 3 with the special name degree Celsius and special symbol °C deserves comment. Because of the way temperature scales used to be defined, it remains common practice to express a thermodynamic temperature, symbol T, in terms of its difference from the reference temperature T0 = 273.15 K, the ice point. This temperature difference is called a Celsius temperature, symbol t, and is defined by the quantity equation
t= T- T0.
The unit of Celsius temperature is the degree Celsius, symbol °C. The numerical value of a Celsius temperature t expressed in degrees Celsius is given by
t/°C = T/K - 273.15.
It follows from the definition of t that the degree Celsius is equal in magnitude to the kelvin, which in turn implies that the numerical value of a given temperature difference or temperature interval whose value is expressed in the unit degree Celsius (°C) is equal to the numerical value of the same difference or interval when its value is expressed in the unit kelvin (K). Thus, temperature differences or temperature intervals may be expressed in either the degree Celsius or the kelvin using the same numerical value. For example, the Celsius temperature difference t and the thermodynamic temperature difference T between the melting point of gallium and the triple point of water may be written as t = 29.7546 °C = T = 29.7546 K.
The special names and symbols of the 22 SI derived units with special names and symbols given in Table 3 may themselves be included in the names and symbols of other SI derived units, as shown in Table 4.