Book:The Information Electricians Need/001. The International System of Units (SI)
Information Electricians Need
The International System of Units (SI)
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Contents
Why SI?
The SI (Système International) is known all around the world as the International System of Units but now, named the Bureau International des Poids et Measures.
It is also known as the MKS system or Mètre, Kilo and Seconds.
Base units
There are seven base units from different disciplines:
| Quantity | Symbol | Abbreviation | Unit |
|---|---|---|---|
| Length | l | m | mètre100 cm <br />1,000 mm <br /> |
| Mass | m | kg | kilogram |
| Time | t | s | second |
| Electric current | I | A | ampere |
| Temperature | T | K | kelvin |
| Luminous intensity | cd | candela | |
| Amount of substance | mol | mole |
What are these quantities?
Meter
- The mètre or meter in english (first of the MKS system) is defined as being equal to 1650763.73 wavelengths of the orange line in the spectrum of a Krypton Discharge Lamp which has been internationally specified.
Kilogram
- The kilogram is defined as being the mass of a platinum-iridium cylinder preserved athe the International Bureau of Weights and Measures à Sèvres, Paris.
Second
- The second is being defined as being the interval occupied by 9192631770 cycles of the radiation corresponding to the transition of the caesium-133 atom.
Ampere
- The ampere is being defined as that current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in a vaccum, would produce between these conductors, a force of 2 * 10-7 newton per meter of length. It is said that the conductors are attracted toward each others if the current are in the same direction and repel each other if the current are in opposite directions.
Kelvin
- The kelvin is defined as being 1/273.16 of the thermodynamic temperature of the triple point of water. When utilizing the Celsius scale, the temperature at which the triple point of water occurs is defined at 0.01°C, so, 0°C=273.15K. A change in temperature of 1°C = a change in temperature of 1K.
Candela
- The candela is defined as being the luminous intensity and it is 600 000 units per square meter of luminance of the platinum standard or better defined as being the luminous intensity, in the perpendicular direction, of a surface of 1/600 000 square meters of a black body at the temperature of freezing platinum under standard atmospheric pressure (oopsy). The luminous intensity of a lamp is defined as the light radiating capacity of a source in a given direction, expressed in candelas. A point of source of light is a source which can with acceptable accuracy be concentrated at a point. A uniform point source of light is a point source emitting light uniformly in all directions.
Mole
- The mole is being defined as the unit of measurement for amount of substance in the International System of Units (SI). A mole of a substance or a mole of particles is defined as exactly 6.02214076×1023 particles, which may be atoms, molecules, ions, or electrons. For particles 1 mol = 6.02214076×1023.
