Physical quantity: A quantity that can be measured by instrument, clearly described and has proper units is called physical value. Physical quantities are defined as fundamental and derived quantities.
Fundamental units: The physical value which does not depend on any other physical quantity is called a fundamental physical quantity such as length; mass and time are called fundamental units.
Derived units: The units that may be derived from fundamental units are called derived units.
Example: Find the acceleration unit?
Solution: Acceleration =velocity/time = v/s = m/S2
System of units: There are three systems of units.
|
Name of system
|
Fundamental unit of
|
|
Length
|
Mass
|
Time
|
|
F.P.S.
|
Foot
|
Pound
|
Second
|
|
C.G.S.
|
Centimetre
|
Gram
|
Second
|
|
M.K.S. (S.I.)
|
Meter
|
Kilogram
|
Second
|
In physics SI system is based on seven fundamental and two supplementary units.
(i) Fundamental units:
|
S.No.
|
Basic Physics
|
Fundamental Unit
|
Symbol
|
|
1.
|
Mass
|
kilogram
|
kg
|
|
2.
|
Length
|
meter
|
m
|
|
3.
|
Time
|
second
|
s
|
|
4.
|
Electric current or Charge
|
ampere or coulomb
|
A or Q
|
|
5.
|
Temperature
|
Kelvin or Celsius
|
K or °C
|
|
6.
|
Luminous intensity
|
candela
|
Cd
|
|
7.
|
Quantity of matter
|
mole
|
Mol
|
(ii) Supplementary units:
|
S.No.
|
Supplementary Physical Quantities
|
Supplementary unit
|
Symbol
|
|
1.
|
Plane angle
|
Radian
|
rad
|
|
2.
|
Solid Angle
|
Steradian
|
sr
|
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