Basic Units and Prefixes for Competitive Exams
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Units of measurement
Base units
The International System of Units (System International d ‘Unites’) is founded on seven base quantities, which are assumed to be mutually independent. These base units are:
Base quantity | SI hast unit | Symbol for unit |
Length | Metre | |
Mass | Kilogram | |
Time | Second | |
Electric Current | Ampere | |
Temperature | Kelvin | |
Amount of substance | Mole | |
Luminous intensity | Candela |
Prefixes
Prefixes are used to form decimal multiples and submultiples of Si units. The common prefixes are:
Factor | Prefix | Symbol |
tera | T | |
giga | G | |
mega | M | |
kilo | k | |
hecto | h | |
deka | da | |
pico | p | |
nano | n | |
micro | μ | |
milli | m | |
centi | c | |
deci | d |
The symbol for a prefix is combined with the unit symbol to which it is attached to form a new unit symbol, e.g. kilometer (km), milligram (mg), microsecond (μs).