Definition of Fundamental Unit

Definitions of Fundamental Units
The seven fundamental units of SI have been defined as under.
1. 1 kilogram A cylindrical prototype mass made of platinum and iridium alloys of height 39 mm
and diameter 39 mm. It is mass of 5.0188 x 10 atoms of carbon-12.
2. 1 metre 1 metre is the distance that contains 1650763.73 wavelength of orange-red light of
Kr-86.
3. 1 second 1 second is the time in which cesium atom vibrates 9192631770 times in an atomic
clock.
4. 1 kelvin 1 kelvin is the (1/273.16) part of the thermodynamics temperature of the triple point
of water.
5. 1 candela 1 candela is (1/60) luminous intensity of an ideal source by an area of cm’ when
source is at melting point of platinum (1760°C).
6. 1 ampere 1 ampere is the electric current which it maintained in two straight parallel
conductor of infinite length and of negligible cross-section area placed one metre apart in
vacuum will produce between them a force 2 x 10 N per metre length.
7. 1 mole 1 mole is the amount of substance of a system which contains a many elementary
entities (may be atoms, molecules, ions, electrons or group of particles, as this and atoms in
0.012 kg of carbon isotope C .

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