JEE Advanced Revision Notes
Physics
Mechanics
Physical Quantities
● A quantity that we can measure is termed a Physical Quantity.
● A physical quantity shall have a numeric value or magnitude which can
represent the exact amount of the object to be measured.
● For e.g. length can be measured in metres, the mass of an object can be
measured in Kgs and so on.
Physical quantities are divided into two types:
1. Fundamental Quantities
2. Derived Quantities
Physical Quantities
S. No Fundamental/Base Quantities Derived Quantities
These quantities are self-sufficient
These quantities do not have their
in nature, which means they need
own identities, they are derived or
1. not depend on other quantities to
expressed in terms of the
completely define themselves.
fundamental quantities.
There are seven Fundamental.
e.g. Length, Time, Mass, Electric
e.g. volume, density, area, velocity,
2. Current, Temperature, Luminous,
acceleration etc.,
intensity, and Amount of substance.
Units
To estimate the size or to measure a physical quantity, we need a reference point
or a reference standard. This point of reference is called a Unit of the given
physical quantity.
Units are divided into two types:
1. Fundamental units
2. Derived units
Class XII Physics www.vedantu.com 1
,Fundamental Units: The unit which gives an idea of the amount or size of the
fundamental Quantities are called Fundamental Units.
Derived Units: The units which give an idea of the amount or size of the Derived
Quantities are called Derived Units.
e.g., Let us consider the unit of speed.
distance travelled
speed
time taken
unit of distance metre
Unit of Speed ms 1
unit of time second
Thus, the unit of speed is derived from fundamental units of length, mass and
time.
Fundamental Quantity Corresponding Unit Symbol
Length metre m
Time second s
Mass kilogram kg
Electric Current ampere A
Temperature kelvin K
Luminous Intensity candela cd
Amount of substance mole mol
Derived Quantity Corresponding Unit Symbol
Area metre2 m2
Volume metre3 m3
Density kilogram/metre3 kg/m3
Velocity metre/second m/s
Acceleration metre/second 2 m/s 2
Electric Potential joule/coulomb or Volt V
Resistance volt/ampere or Ohm Ω
System of Units
Class XII Physics www.vedantu.com 2
, A collection of units which can be used to measure all fundamental and derived
quantities is called a system of units. Some of the most accepted systems of units
are given as follows:
CGS System
The Centimetre-Gram-Second (CGS) System is also called the Gaussian System
of Units. In this system we use centimetre (cm) as unit of length, gram (g) as
unit of mass, and second(s) as unit of time.
For example: Dyne is used as the unit of force in CGS system.
FPS System
The Foot-Pound-Second (FPS) System is a British Engineering System of units.
In this system we use foot (ft) as unit of length, pound (lb) as unit of mass, and
second(s) as unit of time.
For example: Poundal (pdl) is used as the unit of force in FPS system.
MKS System
In the Metre-Kilogram-Second (MKS) System of units, we use metre (m) as unit
of length, kilogram(kg) as unit of mass, and second(s) as unit of time.
Newton is used as the unit of Force.
International System of Units
The International System of Units generally called S.I. units is the latest form of
the metric system. The S.I. system consists of seven fundamental units and two
supplementary units stated below:
Fundamental Unit
Fundamental Quantity S.I. Unit Symbol
Length metre m
Time second s
Mass kilogram kg
Electric Current ampere A
Temperature kelvin K
Luminous Intensity candela cd
Amount of substance mole mol
Class XII Physics www.vedantu.com 3
Physics
Mechanics
Physical Quantities
● A quantity that we can measure is termed a Physical Quantity.
● A physical quantity shall have a numeric value or magnitude which can
represent the exact amount of the object to be measured.
● For e.g. length can be measured in metres, the mass of an object can be
measured in Kgs and so on.
Physical quantities are divided into two types:
1. Fundamental Quantities
2. Derived Quantities
Physical Quantities
S. No Fundamental/Base Quantities Derived Quantities
These quantities are self-sufficient
These quantities do not have their
in nature, which means they need
own identities, they are derived or
1. not depend on other quantities to
expressed in terms of the
completely define themselves.
fundamental quantities.
There are seven Fundamental.
e.g. Length, Time, Mass, Electric
e.g. volume, density, area, velocity,
2. Current, Temperature, Luminous,
acceleration etc.,
intensity, and Amount of substance.
Units
To estimate the size or to measure a physical quantity, we need a reference point
or a reference standard. This point of reference is called a Unit of the given
physical quantity.
Units are divided into two types:
1. Fundamental units
2. Derived units
Class XII Physics www.vedantu.com 1
,Fundamental Units: The unit which gives an idea of the amount or size of the
fundamental Quantities are called Fundamental Units.
Derived Units: The units which give an idea of the amount or size of the Derived
Quantities are called Derived Units.
e.g., Let us consider the unit of speed.
distance travelled
speed
time taken
unit of distance metre
Unit of Speed ms 1
unit of time second
Thus, the unit of speed is derived from fundamental units of length, mass and
time.
Fundamental Quantity Corresponding Unit Symbol
Length metre m
Time second s
Mass kilogram kg
Electric Current ampere A
Temperature kelvin K
Luminous Intensity candela cd
Amount of substance mole mol
Derived Quantity Corresponding Unit Symbol
Area metre2 m2
Volume metre3 m3
Density kilogram/metre3 kg/m3
Velocity metre/second m/s
Acceleration metre/second 2 m/s 2
Electric Potential joule/coulomb or Volt V
Resistance volt/ampere or Ohm Ω
System of Units
Class XII Physics www.vedantu.com 2
, A collection of units which can be used to measure all fundamental and derived
quantities is called a system of units. Some of the most accepted systems of units
are given as follows:
CGS System
The Centimetre-Gram-Second (CGS) System is also called the Gaussian System
of Units. In this system we use centimetre (cm) as unit of length, gram (g) as
unit of mass, and second(s) as unit of time.
For example: Dyne is used as the unit of force in CGS system.
FPS System
The Foot-Pound-Second (FPS) System is a British Engineering System of units.
In this system we use foot (ft) as unit of length, pound (lb) as unit of mass, and
second(s) as unit of time.
For example: Poundal (pdl) is used as the unit of force in FPS system.
MKS System
In the Metre-Kilogram-Second (MKS) System of units, we use metre (m) as unit
of length, kilogram(kg) as unit of mass, and second(s) as unit of time.
Newton is used as the unit of Force.
International System of Units
The International System of Units generally called S.I. units is the latest form of
the metric system. The S.I. system consists of seven fundamental units and two
supplementary units stated below:
Fundamental Unit
Fundamental Quantity S.I. Unit Symbol
Length metre m
Time second s
Mass kilogram kg
Electric Current ampere A
Temperature kelvin K
Luminous Intensity candela cd
Amount of substance mole mol
Class XII Physics www.vedantu.com 3
