Template:Base quantities and count
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Base quantity Symbol for quantity Symbol for dimension Name of SI unit Symbol for SI unit length l L meter m mass m M kilogram kg time t T second s electric current I I ampere A thermodynamic temperature T Θ kelvin K amount of substance* n N mole mol count*,# N C counting unit x luminous intensity Iv J candela cd
- * For the quantities n and N, the entities X have to be specified in the text or indicated by a subscript or in parentheses (IUPAC). Concentration is expressed as amount of substance concentration, cX = nX·V-1 [mol·L-1], count concentration, CX = NX·V-1 [x·L-1], or other formats.
- # 'Count' is synonymous with 'number of entities' and is one of the most fundamental quantities in physics, but the name, symbol and unit are not included in the SI as a base quantity or base unit. Not all sample types contain countable objects. An 'entity', X, is a countable object or event. Countable objects are particles, such as electrons, molecules, packaging units (parcels), cells, organisms, individuals, patients. 'Number of entities' and 'number' are distinguished (in German: Anzahl versus Zahl). The count is not a pure dimensionless number, but the dimension of the count, C, is the entity. The magnitude of a count, N, is expressed by a pure number times the 'counting unit' [x], indicating how many times different members of the defined entity are accounted for in a defined system (not how many times the same member of the defined entity is re-counted in the system — consider the political problem of counting votes), or how many times a defined event is counted during a defined period of time. N is the count [x], and N/t is the frequency (counts per time in units of counting units per second [x·s-1]). A prefix can be used with the unit [x], like with any other symbol of SI units: Mx = 106 x; µx = 10-6 x; Gx = 109 x; nx = 10-9 x.