,
,
, CHAPTER
1 Units and Measurements
2. CGS or Gaussian system: In this system the fundamental
PHYSICAL QUANTITIES quantities are length, mass and time and their respective units
All quantities that can be measured are called physical quantities. are centimetre (cm), gram (g) and second (s).
eg. time, length, mass, force, work done, etc. In physics we study 3. MKS system: In this system also the fundamental quantities
about physical quantities and their inter relationships. are length, mass and time but their fundamental units are
meter (m), kilogram (kg) and second (s) respectively.
MEASUREMENT Table: Units of some physical quantities in different systems
Measurement is the comparison of a quantity with a standard of Type of physical Physical System
the same physical quantity. Different countries followed different Quantity Quantity CGS MKS FPS
standards.
Length cm m ft
Fundamental Mass g kg lb
UNITS
Time s s s
All physical quantities are measured with respect to standard
magnitude of the same physical quantity and these standards are 4. International system (SI) of units: This system is
called UNITS. e.g. second, meter, kilogram, etc. modification over the MKS system. Besides the three base
Four basic properties of units are: units of MKS system four other fundamental and two
1. They must be well defined. supplementary units are also included in this system.
2. They should be easily available and reproducible. Table: SI base quantities and their units
3. They should be invariable e.g. step as a unit of length is not
invariable. S. No. Physical quantity unit Symbol
4. They should be accepted to all. 1 Length metre m
2 Mass kilogram kg
Set of Fundamental Quantities
A set of physical quantities which are completely independent of 3 Time second s
each other but all other physical quantities can be expressed in 4 Temperature kelvin K
terms of these physical quantities is called Set of Fundamental
Quantities. 5 Electric current ampere A
The Fundamental Quantities that are currently being accepted 6 Luminous Intensity candela cd
by the scientific community are mass, time, length, current, 7 Amount of substance mole mol
temperature, luminous intensity and amount of substance.
Derived Physical Quantities Physical Quantity Definition
The physical quantities that can be expressed in terms of (SI Unit)
fundamental physical quantities are called derived physical Length (m) The metre, symbol m, is the SI unit of length.
quantities. E.g. speed = distance/time. It is defined by taking the fixed numerical
System of Units value of the speed of light in vacuum c to
be 299792458 when expressed in the unit
1. FPS or British Engineering system: In this system length,
m s–1, where the second is defined in terms
mass and time are taken as fundamental quantities and their
of the caesium frequency ∆νCs.
base units are foot (ft), pound (lb) and second (s) respectively.
,
, CHAPTER
1 Units and Measurements
2. CGS or Gaussian system: In this system the fundamental
PHYSICAL QUANTITIES quantities are length, mass and time and their respective units
All quantities that can be measured are called physical quantities. are centimetre (cm), gram (g) and second (s).
eg. time, length, mass, force, work done, etc. In physics we study 3. MKS system: In this system also the fundamental quantities
about physical quantities and their inter relationships. are length, mass and time but their fundamental units are
meter (m), kilogram (kg) and second (s) respectively.
MEASUREMENT Table: Units of some physical quantities in different systems
Measurement is the comparison of a quantity with a standard of Type of physical Physical System
the same physical quantity. Different countries followed different Quantity Quantity CGS MKS FPS
standards.
Length cm m ft
Fundamental Mass g kg lb
UNITS
Time s s s
All physical quantities are measured with respect to standard
magnitude of the same physical quantity and these standards are 4. International system (SI) of units: This system is
called UNITS. e.g. second, meter, kilogram, etc. modification over the MKS system. Besides the three base
Four basic properties of units are: units of MKS system four other fundamental and two
1. They must be well defined. supplementary units are also included in this system.
2. They should be easily available and reproducible. Table: SI base quantities and their units
3. They should be invariable e.g. step as a unit of length is not
invariable. S. No. Physical quantity unit Symbol
4. They should be accepted to all. 1 Length metre m
2 Mass kilogram kg
Set of Fundamental Quantities
A set of physical quantities which are completely independent of 3 Time second s
each other but all other physical quantities can be expressed in 4 Temperature kelvin K
terms of these physical quantities is called Set of Fundamental
Quantities. 5 Electric current ampere A
The Fundamental Quantities that are currently being accepted 6 Luminous Intensity candela cd
by the scientific community are mass, time, length, current, 7 Amount of substance mole mol
temperature, luminous intensity and amount of substance.
Derived Physical Quantities Physical Quantity Definition
The physical quantities that can be expressed in terms of (SI Unit)
fundamental physical quantities are called derived physical Length (m) The metre, symbol m, is the SI unit of length.
quantities. E.g. speed = distance/time. It is defined by taking the fixed numerical
System of Units value of the speed of light in vacuum c to
be 299792458 when expressed in the unit
1. FPS or British Engineering system: In this system length,
m s–1, where the second is defined in terms
mass and time are taken as fundamental quantities and their
of the caesium frequency ∆νCs.
base units are foot (ft), pound (lb) and second (s) respectively.
