Electrical Engineering ⇒ Topic : International System of Units

International System of Units

In the International System of units, called SI units, all units used in all branches of science and technology are derived from the following seven basic units.

The above units are defined as follows.

A metre is the length equal to 1650763.73 wavelengths of the orange line in the spectrum of an internationally specified krypton discharge lamp.

A kilogram is the mass of a platinum-iridium cylinder preserved at the International Bureau of Weights and Measures at Sèvres, near Paris.

A second is the interval occupied by 9,192,631,770 cycles of the radiation corresponding to the transition of the Caesium -133 atom.

An ampere is defined as that current which, if maintained in two straight parallel conductors of infinite length of negligible circular cross-section, and placed 1 metre apart in a vacuum, would produce between these conductors a force of

2 x 10^-7 Newton per metre of length.

Kelvin is 1/273.16 of the thermodynamic temperature of the triple point of water. On the Celsius scale, the temperature of the triple point of water is 0.01°C.

Hence                                  0°C = 273.15°K

A temperature interval of 1°C = a temperature interval of 1°K.

The unit mole does not affect the units used in this book