Physics » Notes » Units
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 |
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