Measurement
Tamil Nadu Board · Class 9 · Science
Quick revision notes for Measurement — Tamil Nadu Board Class 9 Science. Key concepts, formulas, and definitions for last-minute revision.
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See them allKey Topics to Revise
1. Physical Quantities and Units
- Physical quantity is any quantity that can be measured and has a numerical value and a unit
- Fundamental quantities cannot be expressed in terms of other quantities - Length, Mass, Time, Temperature, Electric Current, Luminous Intensity, Amount of Substance
- Derived quantities are expressed in terms of fundamental quantities - Area, Volume, Density, Velocity, Force, Pressure, Energy
2. SI Units and Derived Units
- SI System is based on 7 fundamental units and uses metric system with powers of 10
- Length (metre): distance travelled by light in vacuum in 1/299,792,458 second
- Mass (kilogram): defined by international prototype platinum-iridium cylinder kept at Sevres, France
3. Unit Prefixes and Scientific Notation
- Unit prefixes represent powers of 10 and precede unit symbols to specify magnitude
- Large prefixes: Peta (P) = 10¹⁵, Tera (T) = 10¹², Giga (G) = 10⁹, Mega (M) = 10⁶, Kilo (k) = 10³
- Small prefixes: Milli (m) = 10⁻³, Micro (μ) = 10⁻⁶, Nano (n) = 10⁻⁹, Pico (p) = 10⁻¹², Femto (f) = 10⁻¹⁵
4. Rules for Writing SI Units and Symbols
- Units named after scientists: written in lowercase (newton, pascal, joule, tesla), but symbols in uppercase (N, Pa, J, T)
- Units not derived from proper nouns: written and symbolized in lowercase (metre = m, kilogram = kg, second = s)
- No punctuation marks (full stops, hyphens) within or at end of unit symbols - Write '50 m' not '50 m.'
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