Summary Unit and Measurement

Class 11 Physics – Chapter 1: Units and Measurements (Short Notes) • Physical Quantity: A measurable quantity such as length, mass, and time. • Unit: A standard used to measure a physical quantity. • SI Base Units: - 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) • Derived Units: - Speed = m/s - Force = newton (N) - Energy = joule (J) • Dimensions: - Velocity = [M⁰L¹T⁻¹] - Force = [MLT⁻²] • Accuracy: Closeness to the true value. • Precision: Closeness of repeated measurements to each other. • Types of Errors: - Systematic Error - Random Error • Least Count: Smallest value an instrument can measure. • Significant Figures: - All non-zero digits are significant. - Zeros between non-zero digits are significant. - Leading zeros are not significant. - Trailing zeros after a decimal are significant. • Scientific Notation: - 5600 = 5.6 × 10³ - 0.00045 = 4.5 × 10⁻⁴ Important Formulas: - Percentage Error = (Absolute Error / True Value) × 100 - Mean Value = Sum of Observations / Number of Observations Exam Focus: SI Units, Dimensions, Significant Figures, Accuracy vs Precision, and Measurement Errors.