Chapter 1
Units and Measurement
1.1 Introduction
Measurement of any physical quantity involves comparison with a certain
basic, internationally accepted reference standard called unit.
The result of a measurement of a physical quantity is expressed by a
number accompanied by a unit.
Fundamental and Derived Quantities.
The quantities ,which can be measured directly or indirectly are called
physical quantities. There are two types of physical quantities-
Fundamental quantities(Base quantities) and Derived quantities.
▪ The physical quantities, which are independent of each other and
cannot be expressed in terms of other physical qualities are called
fundamental quantities.
Eg: length, mass, time.
▪ The physical quantities , which can be expressed in terms of
fundamental quantities are called derived quantities.
Eg: volume, velocity, force
Fundamental and Derived Units
▪ 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.
▪ The units of the derived quantities are called derived units.
1.2 The International System of Units
A complete set of both the base and derived units, is known as the system
of units. Three such systems, the CGS, the FPS (or British) system and the
MKS system were in use extensively till recently.
The base units for length, mass and time in these systems were as follows :
▪ CGS system - centimetre, gram and second.
▪ FPS system - foot, pound and second.
▪ MKS system - metre, kilogram and second.
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Seema Elizabeth, HSST Physics, MARM Govt HSS Santhipuram
Downloaded from hssreporter.com
, ▪ In 1971 the General Conference on Weights and Measures
developed an internationally accepted system of units for
measurement with standard scheme of symbols, units and
abbreviations.
▪ This is the Système Internationale d’ Unites (French for International
System of Units), abbreviated as SI system.
▪ SI system is now for international usage in scientific, technical,
industrial and commercial work.
In SI system there are seven base units and two supplementary units.
Downloaded from hssreporter.com
,Multiples and Sub multiples of Units
1.3 Significant figures
The result of measurement is a number that includes all digits in the
number that are non reliable plus the first digit that is uncertain.
The reliable digits plus the first uncertain digit in a measurement are
known as significant digits or significant figures.
If the period of oscillation of a symbol pendulum is 1.6 s, the digits 1 and 6
are reliable and certain, while the digit 2 is uncertain
Downloaded from hssreporter.com
, Rule 6: The power of 10, in scientific notation is irrelevant to the
determination of significant figures.
Downloaded from hssreporter.com
Units and Measurement
1.1 Introduction
Measurement of any physical quantity involves comparison with a certain
basic, internationally accepted reference standard called unit.
The result of a measurement of a physical quantity is expressed by a
number accompanied by a unit.
Fundamental and Derived Quantities.
The quantities ,which can be measured directly or indirectly are called
physical quantities. There are two types of physical quantities-
Fundamental quantities(Base quantities) and Derived quantities.
▪ The physical quantities, which are independent of each other and
cannot be expressed in terms of other physical qualities are called
fundamental quantities.
Eg: length, mass, time.
▪ The physical quantities , which can be expressed in terms of
fundamental quantities are called derived quantities.
Eg: volume, velocity, force
Fundamental and Derived Units
▪ 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.
▪ The units of the derived quantities are called derived units.
1.2 The International System of Units
A complete set of both the base and derived units, is known as the system
of units. Three such systems, the CGS, the FPS (or British) system and the
MKS system were in use extensively till recently.
The base units for length, mass and time in these systems were as follows :
▪ CGS system - centimetre, gram and second.
▪ FPS system - foot, pound and second.
▪ MKS system - metre, kilogram and second.
----------------------------------------------------------------------------------
Seema Elizabeth, HSST Physics, MARM Govt HSS Santhipuram
Downloaded from hssreporter.com
, ▪ In 1971 the General Conference on Weights and Measures
developed an internationally accepted system of units for
measurement with standard scheme of symbols, units and
abbreviations.
▪ This is the Système Internationale d’ Unites (French for International
System of Units), abbreviated as SI system.
▪ SI system is now for international usage in scientific, technical,
industrial and commercial work.
In SI system there are seven base units and two supplementary units.
Downloaded from hssreporter.com
,Multiples and Sub multiples of Units
1.3 Significant figures
The result of measurement is a number that includes all digits in the
number that are non reliable plus the first digit that is uncertain.
The reliable digits plus the first uncertain digit in a measurement are
known as significant digits or significant figures.
If the period of oscillation of a symbol pendulum is 1.6 s, the digits 1 and 6
are reliable and certain, while the digit 2 is uncertain
Downloaded from hssreporter.com
, Rule 6: The power of 10, in scientific notation is irrelevant to the
determination of significant figures.
Downloaded from hssreporter.com
