📘 Concept Builder Notes:
Understanding Units, SI System, and Measurement
Build a strong foundation in Physics with these simple and clear notes. This topic is essential for solving real-world problems and preparing for IIT Foundation exams.
🔹 What is Measurement?
- Measurement is the process of comparing an unknown quantity with a known standard.
- All physical quantities (like length, mass, time) are measured using instruments.
🔹 What is a Physical Quantity?
- A property of matter that can be measured.
- Examples: Length, Mass, Time, Temperature, Speed, Force
- Two types:
- Fundamental Quantities: Cannot be derived from others (e.g. length, time).
- Derived Quantities: Formed from fundamental ones (e.g. speed = distance/time).
🔹 What is a Unit?
- A standard quantity used to express a physical quantity.
- Example: Length is measured in metres (m).
- Units must be well-defined and internationally accepted.
🔹 Systems of Units
- Different systems used in history:
- CGS System: Uses centimetre, gram, second.
- FPS System: Uses foot, pound, second.
- MKS System: Uses metre, kilogram, second.
🔹 SI System (International System of Units)
- Adopted in 1960 worldwide.
- Modern version of the MKS system.
- Uses seven basic units:
- Length → metre (m)
- Mass → kilogram (kg)
- Time → second (s)
- Temperature → kelvin (K)
- Electric Current → ampere (A)
- Amount of Substance → mole (mol)
- Luminous Intensity → candela (cd)
- SI units are uniform, universal, and convenient.
🔹 Standard Form and Prefixes
- Used to express very large or very small quantities.
- Examples:
- Kilo (k) = 10³
- Centi (c) = 10⁻²
- Milli (m) = 10⁻³
🔹 Instruments Used in Measurement
- Length: Metre scale, measuring tape, vernier callipers
- Mass: Beam balance, digital balance
- Time: Clock, stopwatch
- Temperature: Thermometer
🔹 Accuracy and Least Count
- Accuracy: Closeness to the true value.
- Precision: Consistency of measurements.
- Least Count: Smallest value measurable by an instrument.
🔹 Errors in Measurement
- Types of Errors:
- Human error
- Instrumental error
- Zero error
- Can be reduced by repetition and careful usage.
🔍 Key Insight: Always use SI units and express final answers with appropriate significant figures and units!
