Basic Electrical and Electronics Engineering Principles

The system of units used in engineering and science is
the Système Internationaled’Unités (International sys
tem of units), usually abbreviated to SI units, and is
based on the metric system. This was introduced in1960
and is now adopted by the majority of countries as the
official system of measurement.
The basic units in the SI system are listed below with
their symbols:

Quantity                                                              Unit
length                                                           metre, m
mass                                                             kilogram,kg
time                                                             second,s
electriccurrent                                             ampere,A
thermodynamictemperature                       kelvin,K
luminousintensity                                        candela,cd
amountofsubstance                                     mole,mol
Derived SI units use combinations of  basic units and
there are many of them. Two examples are:
Velocity – metres per second(m/s)
Acceleration–metres per second
squared(m/s2)
SI units may be made larger or smaller by using prefixes
which denote multiplication or division by a particular
amount. The six most common multiples, with their
meaning, are listed below:
Prefix     Name                   Meaning
M          mega                  multiplyby1000000(i.e.×106)
k            kilo                     multiplyby1000(i.e.×103)
m           milli                    divideby1000(i.e.×10−3)
μ            micro                 divideby1000000(i.e.×10−6)
n            nano                  divideby1000000000
                                        (i.e.×10−9)