UNITS AND MEASUREMENTS

Class 11 Physics – Units and Measurements | Explained by Bibhuti Sir

This chapter is the foundation of all measurements in Physics and is crucial for Class 11 students and aspirants of JEE, NEET, and other competitive exams.

Watch the Full Video of Lecture 1 :

Download Notes and PDF  👉  Units and Measurements 
What You’ll Learn in This Lecture:
1. What Are Physical Quantities?

In Physics, any quantity that can be measured is called a physical quantity. These quantities are broadly classified into:

  • Scalar Quantities – Only magnitude (e.g., mass, temperature)

  • Vector Quantities – Magnitude and direction (e.g., force, velocity)

2. Units and the Need for Standardization

A unit is a standard used to measure a physical quantity. For accurate communication and consistency in science, using standardized units is essential. For example, length is measured in meters (m), mass in kilograms (kg), etc.

3. Types of Units

There are two major types of units:

  • Fundamental (Base) Units – Cannot be derived from other units (e.g., meter, kilogram, second)

  • Derived Units – Formed from combinations of fundamental units (e.g., m/s, N, J)

4. System of Units

Different systems of units are used across the world:

  • CGS – Centimeter-Gram-Second
  • MKS – Meter-Kilogram-Second
  • FPS – Foot-Pound-Second

  • SI System – International System of Units (used globally and in exams like JEE/NEET)

Bibhuti Sir explains why the SI system is considered the most scientific and accepted standard.

5. SI Units – The 7 Base Quantities

The SI system includes 7 base quantities:

Physical Quantity SI Unit Symbol
Length metre m
Mass kilogram kg
Time second s
Electric Current ampere A
Temperature kelvin K
Amount of Substance mole mol
Luminous Intensity candela cd
6. Supplementary Units
  • Plane Angle – measured in radians (rad)

  • Solid Angle – measured in steradians (sr)

7. Derived Units

Examples of derived SI units:

  • Force → Newton (N) = kg·m/s²
  • Energy → Joule (J) = N·m

  • Pressure → Pascal (Pa) = N/m²

8. Dimensions and Dimensional Formulas

Dimensions describe a physical quantity in terms of basic quantities. For example:

  • Force → [M¹L¹T⁻²]

  • Energy → [M¹L²T⁻²]

Dimensional analysis is useful in:

  • Checking correctness of formulas
  • Deriving relations between quantities

  • Converting units from one system to another

Why This Lecture Is Important
  • Builds the foundation for all future Physics concepts
  • Covers concepts relevant for Boards, JEE, NEET, and CUET
  • Helps in understanding how Physics formulas and quantities are connected

  • Teaches how to handle numerical problems using units and dimensions

Learn With Bibhuti Sir – Highlights of the Lecture

✔️ Conceptual clarity with NCERT-based approach
✔️ Hinglish explanation for better understanding
✔️ Useful for Class 11, JEE, NEET, CUET aspirants
✔️ Visual and logical teaching style

Chapter Summary (Quick Recap):
  • Physical quantities = measurable properties in Physics
  • Units are essential to quantify physical quantities
  • SI units = standard across the globe
  • Derived & supplementary units help measure complex quantities
  • Dimensional formulas connect Physics concepts at a deeper level
Useful Links

🔴 Watch Full Video Lecture 1: Click Here!
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