Class 11 Physics - Unit and Measurement

Introduction

• Welcome to Unit and Measurement
• Key Topics for Today:
  • Introduction to the topic
  • Dimensions
  • Various Physical Quantities & Dimensions
• Best notes are self-written; PDF available on the website
• Daily Practice Problem (DPP) to be downloaded from the website

Story: Richard Feynman and the Chessboard Analogy

• Richard Feynman uses a chessboard analogy to explain understanding nature's laws
• Chess pieces (e.g., king, rook, bishop) and their moves represent how scientists decode natural laws
• Each piece represents different aspects and moves of physical quantities
• Figures and positions represent different configurations in nature

Understanding Physical Quantities

• Physical Quantities: Essential to formulating and understanding natural laws
• Can be measured using various instruments
• Comprises numerical value and unit
• Formula: Physical Quantity = Numerical Value * Unit

Fundamental Physical Quantities

• Total 7 Fundamental Physical Quantities:
  • Length
    • Unit: Meter (m)
  • Mass
    • Unit: Kilogram (kg)
  • Time
    • Unit: Second (s)
  • Temperature
    • Unit: Kelvin (K)
  • Electric Current
    • Unit: Ampere (A)
  • Luminous Intensity
    • Unit: Candela (cd)
  • Amount of Substance
    • Unit: Mole (mol)

Derived Physical Quantities

• Formed using the fundamental quantities
• Examples:
  • Area: Square meters (m²), derived from length * length
  • Volume: Cubic meters (m³), derived from length * length * length
  • Velocity: Meters per second (m/s), derived from displacement/time
  • Acceleration: Meters per second squared (m/s²), derived from velocity/time

Supplementary Physical Quantities

• Defined using fundamental quantities
• Two main supplementary quantities: Angle and Solid Angle
  • Angle
    • Unit: Radian
  • Solid Angle
    • Unit: Steradian

Dimensional Analysis

• Dimensions express which fundamental quantities are involved
• Notational system for dimensions: M (Mass), L (Length), T (Time)
• Example:
  • Area: [L²]
  • Volume: [L³]
  • Velocity: [LT⁻¹]
  • Acceleration: [LT⁻²]
  • Force: [MLT⁻²]
  • Work: [ML²T⁻²]

Key Concepts & Definitions

• Physical Quantity: Measurable aspect in nature
• Fundamental Quantity: Basic units of measure
• Derived Quantity: Combined fundamental quantities
• Supplementary Quantity: Additional quantities defined via fundamental quantities
• Dimensional Analysis: Method to understand the composition of physical quantities

Summary

• Today's session introduced Unit and Measurement focusing on dimensions and physical quantities
• Discussed fundamental, derived, and supplementary quantities
• Illustrated with Feynman's chess analogy
• Emphasized the importance of dimensional analysis in physics