Units
To measure a physical quantity we need some standard unit of that quantity. An elephant is heavier than a goat but exactly how many times ? This question can be easily answered if we have chosen a standard mass calling it a unit mass. If the elephant is 200 times the unit mass and the goat is 20 times we know that the elephant is 10 times heavier than the goat.
SI system of units :
Fundamental quantities :
Quantity  Name of the 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 
Supplementary quantities :
Quantity  Name of the Unit  Symbol 
Plane angle  radian  rad 
Solid angle  steradian  sr 
Besides the seven fundamental units two supplementary units are defined.
SI Prefixes :
Power of 10  Prefix  Symbol 
18  exa  E 
15  peta  P 
12  tera  T 
9  gigs  G 
6  mega  M 
3  kilo  k 
2  hecto  h 
1  deka  da 
1  deci  d 
2  centi  c 
3  milli  m 
6  micro  μ 
9  nano  n 
12  pico  p 
15  femto  f 
18  atto  a 
Units & Dimensions – Mcq  Units & Dimensions – Notes  Units & Dimensions – IQ 
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