Chapter - 2 Units and Measurements
Physical quantity
● Any quantity that can be measured
● A physical quantity can be classified in to two:-
1.Fundamental quantity (Base quantity)
2.Derived quantity
● Quantities that cannot be expressed in terms of other quantities are
known as fundamental quantities.Eg:- mass, length, time etc.
● Quantities which are derived from fundamental quantities are known
as derived quantities. Eg:- force, velocity, area, volume ,etc
Unit
● Basic, internationally accepted reference standard used for
measurement is called unit.
● The units for the fundamental or base quantities are called
fundamental or base units.
● The units of all other physical quantities can be expressed as
combinations of the base units.
● Units obtained for the derived quantities are called derived units.
Systems of Units
● A complete set of the base units and derived units, is known as the
system of units.
● In CGS system the base units for length, mass and time were
centimetre, gram and second respectively.
● In FPS system the base units for length, mass and time were foot,
pound and second respectively.
, ● In MKS system the base units for length, mass and time were metre,
kilogram and second respectively.
THE INTERNATIONAL SYSTEM OF UNITS
● SI system is the internationally accepted system of unit at present.
● In SI, there are seven base units and two supplementary units.
SI Units
Sl No Base quantity
Name Symbol
1 Length metre m
2 Mass kilogram kg
3 Time second s
4 Electric Current ampere A
,5 Temperature kelvin K
6 Amount of substance mole mol
7 Luminous intensity candela cd
Sl No Supplementary quantity SI Units
Name symbol
1 Plane angle radian rad
2 Solid angle steradian sr
Plane angle
, The plane angle , s dθ = ds/r
Solid angle
The solid angle , dΩ = ds/r2
Prefixes used with SI units
Prefix Symbol Meaning
Tera – T 1012
Physical quantity
● Any quantity that can be measured
● A physical quantity can be classified in to two:-
1.Fundamental quantity (Base quantity)
2.Derived quantity
● Quantities that cannot be expressed in terms of other quantities are
known as fundamental quantities.Eg:- mass, length, time etc.
● Quantities which are derived from fundamental quantities are known
as derived quantities. Eg:- force, velocity, area, volume ,etc
Unit
● Basic, internationally accepted reference standard used for
measurement is called unit.
● The units for the fundamental or base quantities are called
fundamental or base units.
● The units of all other physical quantities can be expressed as
combinations of the base units.
● Units obtained for the derived quantities are called derived units.
Systems of Units
● A complete set of the base units and derived units, is known as the
system of units.
● In CGS system the base units for length, mass and time were
centimetre, gram and second respectively.
● In FPS system the base units for length, mass and time were foot,
pound and second respectively.
, ● In MKS system the base units for length, mass and time were metre,
kilogram and second respectively.
THE INTERNATIONAL SYSTEM OF UNITS
● SI system is the internationally accepted system of unit at present.
● In SI, there are seven base units and two supplementary units.
SI Units
Sl No Base quantity
Name Symbol
1 Length metre m
2 Mass kilogram kg
3 Time second s
4 Electric Current ampere A
,5 Temperature kelvin K
6 Amount of substance mole mol
7 Luminous intensity candela cd
Sl No Supplementary quantity SI Units
Name symbol
1 Plane angle radian rad
2 Solid angle steradian sr
Plane angle
, The plane angle , s dθ = ds/r
Solid angle
The solid angle , dΩ = ds/r2
Prefixes used with SI units
Prefix Symbol Meaning
Tera – T 1012
