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International System Of Units

The International System of Units (abbreviated "SI") is a scientific method of expressing the magnitudes of seven important natural phenomena. This system was formerly called the meter-kilogram-second (MKS) system. All SI units can be expressed as a standard multiple, fractional quantity, and also directly. Multiple and fractional SI units are defined by prefix multipliers in powers of 10 ranging from 10-24 to 1024.


International System of Units

Ampere: (abbreviation, A)

Ampere is the SI unit of electric current. One ampere is the current that would produce a force of 0.0000002 (2 x 10-7) Newton between two straight, parallel, perfectly conducting wires having infinite length and zero diameter, separated by one meter in a vacuum. One ampere represents 6.24 x 1018 unit electric charge carriers, such as electrons, passing a specified fixed point in one second.

Candela: (abbreviation, cd)

Candela is the SI unit of luminous intensity. It is the electromagnetic radiation, in a specified direction, that has an intensity of 1/683 (1.46 x 10-3) watt per steradian at a frequency of 540 terahertz (5.40 x 1014 hertz). Note: A steradian is a unit of measure equal to the solid angle subtended at the center of a sphere by an area on the surface of the sphere that is equal to the radius squared.

Kelvin: (abbreviation K), also called the degree Kelvin (abbreviation, oK)

Kelvin is the SI unit of temperature. One Kelvin is 1/273.16 (3.6609 x 10-3) of the thermodynamic temperature of the triple point of pure water (H2O).

Kilogram: (abbreviation, kg)

Kilogram is the SI unit of mass. It is defined as the mass of a particular international prototype made of platinum-iridium and kept at the International Bureau of Weights and Measures. It was originally defined as the mass of one liter (10-3 cubic meter) of pure water.

Meter: (abbreviation, m)

Meter is the SI unit of displacement or length. One meter is the distance traveled by a ray of electromagnetic (EM) energy through a vacuum in 1/299,792,458 (3.33564095 x 10-9) second. The meter was originally defined as one ten-millionth (0.0000001 or 10-7) of the distance, as measured over the earth's surface in a great circle passing through Paris, France, from the geographic north pole to the equator.

Mole: (abbreviation, mol)

Mole is the SI unit of material quantity. One mole is the number of atoms in 0.012 kilogram of the most common isotope of elemental carbon (C-12). This is approximately 6.022169 x 1023, and is also called the Avogadro constant.

Second: (abbreviation, s or sec)

Second is the SI unit of time. One second is the time that elapses during 9.192631770 x 109 cycles of the radiation produced by the transition between two levels of Cesium 133. It is also the time required for an EM field to propagate 299,792,458 (2.99792458 x 108) meters through a vacuum.


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