CLASS 11 PHYSICS
Chapter: Units & Measurements
Exam-Ready Notes + Formula Sheet + Common Traps + Practice
Based on the NCERT Class XI Physics syllabus
1. THE CHAPTER IN ONE MINUTE
Physics is built on measurement.
Whenever we measure a physical quantity, we compare it with an agreed
standard called a unit.
Every physical quantity can be represented as:
Physical quantity = numerical value × unit
Example:
5 m = 5 × metre
Here:
,5 → numerical value
metre → unit
The core ideas of this chapter
Units → Measurement → Errors → Significant Figures → Dimensions →
Dimensional Analysis
If you understand these six ideas, most questions from this chapter become
straightforward.
2. PHYSICAL QUANTITIES
A physical quantity is a quantity that can be measured and expressed numerically.
Examples:
a) length
b) mass
c) time
d) speed
e) force
f) energy
g) temperature
Physical quantities are broadly divided into:
,Fundamental quantities
These are quantities that are independent of one another.
The SI system has 7 base quantities.
BASE QUANTITY SI UNIT SYMBOL
Length Meter (m)
Mass Kilogram (kg)
Time Second (s)
Thermodynamic temperature Kelvin (K)
Electric current Ampere (A)
Amount of Substance Mole (mol)
Luminous Intensity Candela (cd)
Derived quantities
These are obtained from fundamental quantities using mathematical relations.
Examples:
1. Velocity:
Velocity = displacement / time
SI unit: m s⁻¹
2. Force:
Force = mass × acceleration
, SI unit: kg m s⁻² = Newton (N)
3. SI SYSTEM OF UNITS
The International System of Units (SI) is the internationally accepted system of
measurement.
Important SI units to remember:
QUANTITY SI UNIT
Length Meter (m)
Mass Kilogram (kg)
Time Second (s)
Temperature Kelvin (K)
Force Newton (N)
Work/Energy Joule (J)
Power Watt (W)
Pressure Pascal (Pa)
Frequency Hertz (Hz)
Electric Charge Coulomb (C)
Exam trap:
The SI base unit of mass is kilogram, NOT gram.
That is a common MCQ trap.
4. SI PREFIXES
Prefixes allow us to express very large or very small quantities conveniently.
Chapter: Units & Measurements
Exam-Ready Notes + Formula Sheet + Common Traps + Practice
Based on the NCERT Class XI Physics syllabus
1. THE CHAPTER IN ONE MINUTE
Physics is built on measurement.
Whenever we measure a physical quantity, we compare it with an agreed
standard called a unit.
Every physical quantity can be represented as:
Physical quantity = numerical value × unit
Example:
5 m = 5 × metre
Here:
,5 → numerical value
metre → unit
The core ideas of this chapter
Units → Measurement → Errors → Significant Figures → Dimensions →
Dimensional Analysis
If you understand these six ideas, most questions from this chapter become
straightforward.
2. PHYSICAL QUANTITIES
A physical quantity is a quantity that can be measured and expressed numerically.
Examples:
a) length
b) mass
c) time
d) speed
e) force
f) energy
g) temperature
Physical quantities are broadly divided into:
,Fundamental quantities
These are quantities that are independent of one another.
The SI system has 7 base quantities.
BASE QUANTITY SI UNIT SYMBOL
Length Meter (m)
Mass Kilogram (kg)
Time Second (s)
Thermodynamic temperature Kelvin (K)
Electric current Ampere (A)
Amount of Substance Mole (mol)
Luminous Intensity Candela (cd)
Derived quantities
These are obtained from fundamental quantities using mathematical relations.
Examples:
1. Velocity:
Velocity = displacement / time
SI unit: m s⁻¹
2. Force:
Force = mass × acceleration
, SI unit: kg m s⁻² = Newton (N)
3. SI SYSTEM OF UNITS
The International System of Units (SI) is the internationally accepted system of
measurement.
Important SI units to remember:
QUANTITY SI UNIT
Length Meter (m)
Mass Kilogram (kg)
Time Second (s)
Temperature Kelvin (K)
Force Newton (N)
Work/Energy Joule (J)
Power Watt (W)
Pressure Pascal (Pa)
Frequency Hertz (Hz)
Electric Charge Coulomb (C)
Exam trap:
The SI base unit of mass is kilogram, NOT gram.
That is a common MCQ trap.
4. SI PREFIXES
Prefixes allow us to express very large or very small quantities conveniently.
