10 2.5 The International System of Units (SI)
- The SI is the modern metric system.
- At the 11th General Conference on Weights and Measures (1960) it was agreed to add four more base units to the old metric system (M.K.S), giving seven base quantities:
11
Fundamental quantity
- Length
Symbol
- L
SI unit
- metre
Unit symbol
- m
22
Fundamental quantity
- Mass
Symbol
- M
SI unit
- kilogram
Unit symbol
- kg
33
Fundamental quantity
- Time
Symbol
- t (T)
SI unit
- second
Unit symbol
- s
44
Fundamental quantity
- Electric current intensity
Symbol
- I
SI unit
- ampere
Unit symbol
- A
55
Fundamental quantity
- Absolute (thermodynamic) temperature
Symbol
- T
SI unit
- kelvin
Unit symbol
- K
66
Fundamental quantity
- Amount of substance
Symbol
- n
SI unit
- mole
Unit symbol
- mol
77
Fundamental quantity
- Luminous intensity
Symbol
- Iv
SI unit
- candela
Unit symbol
- cd
Two supplementary units are also included:
- the radian (rad) — the unit of plane angle,
- the steradian (sr) — the unit of solid angle (the angle of a cone-like region in space, as seen from its apex).
- The SI is used consistently in all scientific fields all over the world.
- In this book, unless told otherwise, you should convert every given value to SI units before substituting in an equation.