## Base Units

The International System of Units (SI) defines seven units as a basic set from which all other SI units are derived. These SI base units and their physical quantities are:

metre for length

kilogram for mass

second for time

ampere for electric current

kelvin for temperature

candela for luminous intensity

mole for the amount of substance.

The SI base quantities form a set of mutually independent dimensions as required by dimensional analysis.

Metre, m | length | of the distance travelled by light in one second. |

Kilogran, kg | mass | Equal to the mass of the international prototype of the kilogram |

Second, s | time | Duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of caesium 133. |

ampere, A | electric current | The current through each of two straight parallel conductors of infinite length, negligible cross-section, 1 metre apart in a vacuum, which would a force equal tonewton per metre of length |

Kelvin, K | Absolute temperature | Equal to the fraction 1/273.16 of the thermodynamic temperature of the triple point of water |

Mole, mol | amount of substance | The amount of substance which contains as many elementary entities - atoms, molecules, ions, electrons, other particles, or specified groups of such particles - as atoms in 12g carbon 12 |

Candela, cd | luminosity | The luminous intensity of a source that emits monochromatic radiation of frequencyhertz and that has a radiant intensity in that direction of 1/683 watt per steradia (solid angle). |