SI Units

The Systeme International d'Unites (SI) has been adopted and is defined by IS0 1000.

Meter (m).
The meter is the length equal to 1 650 753.73 wavelengths in vacuum of the radiation corresponding to the transition
between the levels 2p10 and 5d5 of the krypton-86 atom.

Kilogram  (kg).
The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

Second (s).
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

Ampere (A).
The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum, would produce between these conductors a force equal to 2 x 10-7 newtons per metre of length.

Kelvin (K).
The kelvin, unit of thermodynamic temperature, is the fraction U273.16 of the thermodynamic temperature of the triple point of water.

Candela (cd).
The candela is the luminous intensity, in the perpendicular direction, of a surface of 1/600 000 m2 of a black body at the temperature of freezing platinum under a pressure of 101 325 newtons per square metre.

The supplementary base units are defined as follows:

Plane angle (radian).
The angle subtended at the centre of a circle of radius 1 m by an arc of length 1 m along the circumference.

Solid angle (steradian).
The solid angle subtended at the centre of' a sphere of radius 1 m by an area of 1 m2 on the surface.

Mole (mol).

It is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of carbon-12. The elementary entities must be specified and can be atom molecules, ion electrons, other particles or specified groups of such particles.

About The Author:
He is a marine engineer sailing with British Petroleum.He has keen interest on compiling marine exam notes.
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