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INTERMEDIATE PHYSICS – LESSON 1

UNITS & MEASUREMENTS

1. Introduction

Physics is a science based on measurement. To express any physical quantity, we need:

A numerical value
A unit

Example: Length = 5 m
The number 5 has no meaning without the unit metre.

2. Measurement

Measurement is the process of comparing an unknown physical quantity with a known standard quantity called a unit.

3. Physical Quantities

A physical quantity is any quantity that can be measured.

Types of Physical Quantities:

Fundamental quantities
Derived quantities

4. Fundamental Physical Quantities (SI System)

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

These seven quantities are independent and form the basis of the SI system.

5. Derived Quantities

Derived quantities are obtained from fundamental quantities.

Velocity = Distance / Time (m/s)
Acceleration = Velocity / Time (m/s²)
Force = Mass × Acceleration (N)
Pressure = Force / Area (Pa)

6. Dimensional Formula

A dimensional formula represents a physical quantity in terms of fundamental dimensions:

Mass → M
Length → L
Time → T

Example:
Force = Mass × Acceleration
Dimensional formula of force = [M L T^-2]

Uses of Dimensional Formula:

To check correctness of equations
To convert units
To derive relations between quantities

7. Errors in Measurement

The difference between the true value and the measured value is called error.

Types of Errors:

Absolute error
Mean error
Percentage error

Percentage Error:

Percentage Error = (Absolute Error / Measured Value) × 100

8. Significant Figures

Significant figures indicate the accuracy of a measurement.

All non-zero digits are significant
Zeros between non-zero digits are significant
Leading zeros are not significant
Trailing zeros after decimal are significant

Example:
0.00450 has 3 significant figures

9. Measuring Instruments

(a) Vernier Calipers

Used to measure length, diameter, and thickness.

Least Count:
LC = (1 Main Scale Division) / (Number of Vernier divisions)

(b) Screw Gauge

Used to measure diameter of thin wires and thickness of sheets.

Least Count:
LC = Pitch / Number of circular scale divisions

10. Important Points for Intermediate Exam

Learn SI units and symbols thoroughly
Practice numerical problems on errors
Remember dimensional formulas
Write answers neatly with proper units

Next Lesson: Motion in a Straight Line

Intermediate Physics Complete Notes – IIT JEE & Board Exams

This page contains complete Intermediate Physics notes along with IIT JEE materials, previous year questions, solved problems, diagrams, and exam strategies.

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