Units

Units

The chosen standard used for measuring a physical quantity is called unit.

System of Units

Few internationally accepted systems are

1. CGS system
2. FPS System
3. SI Units.

SI Base Units

There are 7 Base Units in SI system. They are –

Base Quantity	Unit	Symbol
Length	Metre	m
Mass	Kilogram	kg
Time	Second	s
Electric Current	Ampere	A
Thermodynamic temperature	Kelvin	K
Amount of substance	Mole	mol
Luminous intensity	Candela	cd

SI Supplementary Units

Supplementary Quantity	Unit	Symbol
Plane angle	Radian	rad
Solid angle	Steradian	Sr

Standard Units

viscocity	pascal second
Power	dioptre
Inductance	henry
Loudness	phon
Magnetic inductance	tesla
Magnetic flux	weber
Electric charge	coulomb

Important Prefixes to Units

1. 1. Tera (T) ➟ 10¹²
   2. Giga (G) ➟ 10⁹
   3. Mega (M) ➟ 10⁶
   4. kilo (K) ➟ 10³
   5. hecto (h) ➟ 10²
   6. deka (da) ➟ 10
   7. deci (d) ➟ 10^–1
   8. centi (C) ➟ 10^–2
   9. mili (m) ➟ 10^–3
   10. Micro (µ) ➟ 10^–6
   11. nano (n) ➟ 10^–9
   12. Pilo (P) ➟ 10^–12
   13. Femp (f) ➟ 10^–15
   14. atto (a) ➟ 10^–18