Units
A unit is an internationally accepted standard for measurements of quantities.
- Measurement consists of a numeric quantity along with a relevant unit.
- Units for Fundamental or base quantities (like length, time etc.) are called Fundamental units.
- Units which are combination of fundamental units are called Derived units.
- Fundamental and Derived units together form a System of Units.
- Internationally accepted system of units is SystèmeInternationale d’ Unites (French for International system of Units) or SI. It was developed and recommended by General Conference on Weights and Measures in 1971.
- SI lists 7 base units as in the table below. Along with it, there are two units - radian or rad (unit for plane angle) and steradian or sr (unit for solid angle). They both are dimensionless.
|
Base Quantity
|
Name
|
Symbol
|
|
Length
|
metre
|
m
|
|
Mass
|
kilogram
|
kg
|
|
Time
|
second
|
s
|
|
Electric Current
|
ampere
|
A
|
|
Thermo dynamic Temperature
|
kelvin
|
K
|
|
Amount of Substance
|
mole
|
mol
|
|
Luminous intensity
|
candela
|
cd
|
