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metre [m]
The metre is the basic unit of length. It is the distance light travels, in a
vacuum, in 1/299792458th of a second.
kilogram [kg]
The kilogram is the basic unit of mass. It is the mass of an international
prototype in the form of a platinum-iridium cylinder kept at Sevres in France.
It is now the only basic unit still defined in terms of a material object, and
also the only one with a prefix [kilo] already in place.
second [s]
The second is the basic unit of time. It is the length of time taken for
9192631770 periods of vibration of the caesium-133 atom to occur.
ampere [A]
The ampere is the basic unit of electric current. It is that current which
produces a specified force between two parallel wires which are 1 metre apart in
a vacuum. It is named after the French physicist Andre Ampere (1775-1836).
kelvin [K]
The kelvin is the basic unit of temperature. It is 1/273.16th of the
thermodynamic temperature of the triple point of water. It is named after the
Scottish mathematician and physicist William Thomson 1st Lord Kelvin
(1824-1907).
mole [mol]
The mole is the basic unit of substance. It is the amount of substance that
contains as many elementary units as there are atoms in 0.012 kg of carbon-12.
candela [cd]
The candela is the basic unit of luminous intensity. It is the intensity of a
source of light of a specified frequency, which gives a specified amount of
power in a given direction. |
