Physics notes ncert

Chapter 2: Units and Measurements – Notes


1. Physical Quantities


Quantities that can be measured and described by laws of physics.




Examples: Length, mass, time, temperature, electric current.




2. Units


Fundamental Units: Cannot be derived from other units.


Example: metre (m), kilogram (kg), second (s), ampere (A).




Derived Units: Derived from fundamental units.


Example: Newton (N) = kg·m/s².




3. System of Units


System Length Mass Time


CGS cm g s


FPS ft lb s

,MKS m kg s


SI m kg s


SI Units (International System of Units) are widely used.




4. SI Base Units (7 Units)


Quantity Unit (Symbol) Name


Length m metre


Mass kg kilogram


Time s second


Electric Current A ampere


Temperature K kelvin


Luminous Intensity cd candela


Amount of Substance mol mole


5. Measurement of Length, Mass, and Time


Length: Measured using vernier calipers, screw gauge, metre scale.




Mass: Beam balance, electronic balance.

, Time: Atomic clock (most accurate), stopwatch, pendulum.




6. Accuracy, Precision, and Errors


Error Types


Systematic Error: Repeatable, due to faulty equipment or method.




Random Error: Due to unknown and unpredictable factors.




Absolute Error:




Δ


x




=




x


i