SI Units

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
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
    100
deca da 101
hecto h 102
kilo k 103
mega M 106
giga G 109
tera T 1012
peta P 1015
exa E 1018
zetta Z 1021
yotta Y 1024

Example :

Youngs Modulus of Mild Steel= 210 Gpa -> -> 210 x 109 N/m2 



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