Understanding the basics of physics begins with mastering the core concepts of measurement. This is why Chapter 1: Units and Measurements – IIT Bombay Physics Notes plays a foundational role for every engineering and science aspirant. In this chapter, students learn how to define physical quantities, choose appropriate units, and understand the importance of accuracy, precision, and dimensional analysis. Whether you’re preparing for JEE, NEET, or just want to build a strong base in physics, this chapter is essential for developing your problem-solving and analytical skills.
Chapter 1: Units and Measurements – IIT Bombay Physics Notes explains key topics like SI units, fundamental and derived quantities, types of errors, and significant figures in a student-friendly and structured manner. With practical examples and easy-to-understand language, these notes are designed to help you grasp each concept clearly and retain it for long-term learning. These notes follow the academic approach of IIT Bombay and are ideal for students aiming for top ranks in competitive exams. If you’re looking for high-quality and SEO-optimized physics study material, this is the perfect place to begin your journey with Chapter 1: Units and Measurements – IIT Bombay Physics Notes.
1. Physical Quantities
Physical quantity means any quantity that can be measured and expressed in numbers. जैसे – length, mass, time, temperature, current, etc.
2. Types of Physical Quantities
- Fundamental quantities – जिनको independently measure किया जा सकता है। Example: length, mass, time, temperature, current, luminous intensity, amount of substance.
- Derived quantities – जो fundamental quantities से बनते हैं। Example: speed, area, volume, force, etc.
3. Units
Unit means standard quantity used to measure any physical quantity.
Types of Units
- Fundamental units – जैसे metre (m), kilogram (kg), second (s), etc.
- Derived units – जैसे m/s, m², N (Newton), etc.
- Supplementary units – plane angle (radian), solid angle (steradian)
System of Units
- CGS system – cm, gram, second
- MKS system – metre, kilogram, second
- SI system – International system (used worldwide)
4. Dimensions
Dimension means the power to which a fundamental quantity is raised in a physical quantity.
Example:
Speed = distance / time
= [L]/[T] = [L¹ T⁻¹]
So, speed की dimension = [L¹ M⁰ T⁻¹]
5. Dimensional Formula
It shows the dependency of a physical quantity on fundamental quantities.
Example:
Force = mass × acceleration = [M][L][T⁻²] = [M¹ L¹ T⁻²]
6. Applications of Dimensional Analysis
- To check correctness of equation (principle of homogeneity)
- To derive formulas
- To convert units
7. Accuracy, Precision, and Errors
(a) Accuracy – कितनी सही value है actual value के करीब।
(b) Precision – कितनी बार same या close result आता है repeat करने पर।
(c) Errors – Difference between measured and true value.
Types of Errors
- Systematic error – Same pattern में होती है, fix होती है
- Random error – बिना pattern के आती है
- Gross error – Human mistake या instrument failure
8. Significant Figures
Significant figures = सही digits + first doubtful digit
Rules:
- Non-zero digits हमेशा significant होते हैं
- Zeros between digits are significant
- Trailing zeros after decimal are significant
Example:
- 1.500 → 4 significant figures
- 1500 → 2 significant figures (unless specified)
9. Rounding Off
Last digit को round करते हैं based on next digit:
- 0–4 → no change
- 5–9 → increase by 1
