**International System of Units**

The modified or developed form of Metric System (one of the system of units for measurement consist of three fundamental units which are meter, kilogram, second) is called as **International System of Units **or **SI Units**. SI Units are considered as standard units of measurement and are most widely used. SI Units are classified into base or fundamental units and derived units.

**Base or Fundamental Units**

QUANTITY |
UNIT |
SYMBOL |

Length | meter | m |

Mass | kilogram | kg |

Time | second | s |

Temperature | kelvin | K |

Electric Current | ampere | A |

Amount of Substance | mole | mol |

Intensity of Luminous | candela | cd |

**Derived Units**

These units are derived from fundamental or base units. We can derive infinite number of derived units from base units. Some of the examples of derived units are

QUANTITY |
UNIT |
SYMBOL |

Weight or Force | newton | N |

Energy(Work, Heat) | joule | J |

Pressure, Stress | pascal | Pa |

Heat Flow Rate,Mechanical Power | watt | W |

Frequency | hertz | Hz |

Electric Charge | coulomb | C |

Voltage | volt | V |

Magnetic Field | tesla | T |

Electric Resistance | ohm | Ω |

Angle | radian | rad |

Electric Capacitance | farad | F |

Magnetic Flux | weber | Wb |

**Prefixes used in SI units**

Prefix Name |
Prefix Symbol |
Prefix Value |

yocto | y | 10^{-24} |

zepto | z | 10^{-21} |

atto | a | 10^{-18} |

femto | f | 10^{-15} |

pico | p | 10^{-12} |

nano | n | 10^{-9} |

micro | µ | 10^{-6} |

milli | m | 10^{-3} |

centi | c | 10^{-2} |

deci | d | 10^{-1} |

10^{0} |
||

deca | da | 10^{1} |

hecto | h | 10^{2} |

kilo | k | 10^{3} |

mega | M | 10^{6} |

giga | G | 10^{9} |

tera | T | 10^{12} |

peta | P | 10^{15} |

exa | E | 10^{18} |

zetta | Z | 10^{21} |

yotta | Y | 10^{24} |

Example :

Youngs Modulus of Mild Steel= 210 Gpa -> -> 210 x 10^{9 }N/m^{2}^{ }