Unit: The chosen
standard used for measuring a physical quantity is called unit.
Unit should be:
(i)
Well defined
(ii)
Easy to reproduce
(iii)
Easy to compare
(iv)
Independent of changes in physical conditions
(v)
Internationally accepted
Units are of two
types – (i) Fundamental Unit; (i) Derived Unit
System of units _
Unites depend on choice. Each choice of units leads to a new system (set) of
units. The internationally accepted systems are (i) CGS system, (ii) MKS System
(iii) FPS system (iv) SI Units.
In SI Units,
there are seven fundamental units given in the following
|
Physical Quantity
|
Si Unit
|
Symbol
|
|
Length
|
Metre
|
m
|
|
Mass
|
Kilogram
|
kg
|
|
Time
|
Second
|
s
|
|
Electric current
|
Ampere
|
A
|
|
Temperature
|
Kelvin
|
K
|
|
Luminuous intensity
|
Candela
|
Cd
|
|
Amount of substance
|
mole
|
mol
|
Besides these seven fundamental units, two supplementary
units are also defined, viz, radian [rad] for plane angle and steradian (sr)
for solid angle.
