Fundamental And Derived Quantities

Fundamental and Derived Quantities

• The quantities that are independent of other quantities are called fundamental quantities. The units that are used to measure these fundamental quantities are called fundamental units. There are four systems of units namely C.G.S [centimeter(cm), gram(gm), second(sec)], M.K.S [metre(m), kilogram(kg), second(sec)], F.P.S [foot, pound, second] and Si [International system of units].
• The quantities that are derived using the fundamental quantities are called derived quantities. The units that are used to measure these derived quantities are called derived units.

Fundamental and Supplementary physical quantities in SI system:

Unit and symbol of quantities:

Practical units

• Length
  • 1 angstrom = 1A = 10^-10= 10 cm 10 mm 0.1 mm
  • 1 micron = um = 10^-6 m
  • 1 Light year = 1 ly = 9.46 x 10¹⁵ m
  • 1 Parsec 1pc = 3.26 light year
• Mass
  • Metric tonne: 1 Metric tonne 1000 kg
  • Quintal: 1 Quintal = 100 kg
  • Atomic mass unit (AMU) : AMU = 1.67 x 10^-27kg
• Time
  • 1 year = 365.25 days = 3.156 x 10⁷ sec.
  • 1 solar year = 365.25 average solar day
  • Average solar day = 1/365.25 the part of a solar year